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Epistemology (; ) is the branch of philosophy concerned with
knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is something that is truth, true. The usual test for a statement of fact is verifiability—that is whether it can be demonstrated to correspond to e ...
. Epistemologists study the nature, origin, and scope of knowledge, epistemic justification, the
rationality Rationality is the quality or state of being rational – that is, being based on or agreeable to reason Reason is the capacity of consciously applying logic Logic is an interdisciplinary field which studies truth and reasoning Reaso ...
of
belief A belief is an attitude Attitude may refer to: Philosophy and psychology * Attitude (psychology) In psychology Psychology is the science of mind and behavior. Psychology includes the study of consciousness, conscious and Unconsci ...

belief
, and various related issues. Epistemology is considered a major subfield of philosophy, along with other major subfields such as
ethics Ethics or moral philosophy is a branch of philosophy Philosophy (from , ) is the study of general and fundamental questions, such as those about Metaphysics, existence, reason, Epistemology, knowledge, Ethics, values, Philosophy of mind, ...

ethics
,
logic Logic is an interdisciplinary field which studies truth and reasoning. Informal logic seeks to characterize Validity (logic), valid arguments informally, for instance by listing varieties of fallacies. Formal logic represents statements and ar ...

logic
, and
metaphysics Metaphysics is the branch of philosophy that studies the first principles of being, identity and change, space and time, causality, necessity and possibility. It includes questions about the nature of consciousness and the relationship between ...

metaphysics
. Debates in epistemology are generally clustered around four core areas: # The
philosophical analysis Philosophical analysis refers to a set of techniques, typically used by philosophers in the analytic tradition, in order to "break down" (i.e. analyze) philosophical issues. Arguably the most prominent of these techniques is the analysis of conce ...
of the nature of knowledge and the conditions required for a belief to constitute knowledge, such as
truth Truth is the property of being in accord with fact A fact is something that is true True most commonly refers to truth Truth is the property of being in accord with fact or reality.Merriam-Webster's Online Dictionarytruth 2005 In ...

truth
and justification # Potential sources of knowledge and justified belief, such as
perception Perception (from the Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" o ...

perception
,
reason Reason is the capacity of consciously applying logic Logic is an interdisciplinary field which studies truth and reasoning Reason is the capacity of consciously making sense of things, applying logic Logic (from Ancient Greek, Greek ...
,
memory Memory is the faculty of the brain A brain is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exis ...

memory
, and
testimony In law and in religion, testimony is a solemn attestation as to the truth of a matter. Etymology The words "testimony" and "testify" both derive from the Latin word ''testis'', referring to the notion of a disinterested Third-party source, thir ...

testimony
# The structure of a body of knowledge or justified belief, including whether all justified beliefs must be derived from justified foundational beliefs or whether justification requires only a coherent set of beliefs #
Philosophical skepticism Philosophical skepticism (American and British English spelling differences, UK spelling: scepticism; from Ancient Greek, Greek σκέψις ''skepsis'', "inquiry") is a family of Philosophy, philosophical views that question the possibility o ...
, which questions the possibility of knowledge, and related problems, such as whether skepticism poses a threat to our ordinary knowledge claims and whether it is possible to refute skeptical arguments In these debates and others, epistemology aims to answer questions such as "What do we know?", "What does it mean to say that we know something?", "What makes justified beliefs justified?", and "How do we know that we know?".


Background


Etymology

The word ''epistemology'' is derived from the ancient Greek ''epistēmē'', meaning "knowledge", and the suffix ''-logia'', meaning "logical
discourse Discourse is a generalization of the notion of a conversation Conversation is interactive communication Communication (from Latin ''communicare'', meaning "to share") is the act of developing Semantics, meaning among Subject (philosophy) ...

discourse
" (derived from the Greek word ''logos'' meaning "discourse"). The word's appearance in English was predated by the German term ''Wissenschaftslehre'' (literally, theory of science), which was introduced by philosophers
Johann Fichte Johann Gottlieb Fichte (; ; 19 May 1762 – 29 January 1814) was a German philosopher A philosopher is someone who practices philosophy. The term ''philosopher'' comes from the grc, φιλόσοφος, , translit=philosophos, meaning 'lover ...
and
Bernard Bolzano Bernard Bolzano (, ; ; ; born Bernardus Placidus Johann Nepomuk Bolzano; 5 October 1781 – 18 December 1848) was a Bohemian A Bohemian () is a resident of Bohemia Bohemia ( ; cs, Čechy ; ; hsb, Čěska; szl, Czechy) is the westernmost a ...

Bernard Bolzano
in the late 18th century. The word "epistemology" first appeared in 1847, in a review in New York's ''Eclectic Magazine''. It was first used as a translation of the word ''Wissenschaftslehre'' as it appears in a philosophical novel by German author
Jean Paul Jean Paul (; born Johann Paul Friedrich Richter, 21 March 1763 – 14 November 1825) was a German Romantic , (1774–1840)''Moonrise by the Sea,'' 1822, 55x71 cm German Romanticism was the dominant intellectual movement of German-speaking co ...

Jean Paul
: The word "epistemology" was properly introduced into Anglophone philosophical literature by Scottish philosopher
James Frederick Ferrier James Frederick Ferrier (16 June 1808 – 11 June 1864) was a Scottish metaphysical Metaphysics is the branch of philosophy that examines the fundamental nature of reality, including the relationship between mind and matter, between sub ...

James Frederick Ferrier
in 1854, who used it in his ''Institutes of Metaphysics'': It is important to note that the French term ''épistémologie'' is used with a different and far narrower meaning than the English term "epistemology", being used by French philosophers to refer solely to
philosophy of science Philosophy of science is a branch of philosophy concerned with the foundations, methodology, methods, and implications of science. The central questions of this study concern Demarcation problem, what qualifies as science, the reliability of s ...
. For instance,
Émile Meyerson Émile Meyerson (; 12 February 1859 – 2 December 1933) was a Polish-born French epistemologist, chemist, and philosopher of science. Meyerson was born in Lublin, Poland Poland ( pl, Polska ), officially the Republic of Poland ( pl, Rzec ...
opened his ''Identity and Reality'', written in 1908, with the remark that the word 'is becoming current' as equivalent to 'the philosophy of the sciences.'


History of epistemology

Epistemology, as a distinct field of inquiry, predates the introduction of the term into the lexicon of philosophy.
John Locke John Locke (; 29 August 1632 – 28 October 1704) was an English philosopher and physician, widely regarded as one of the most influential of Enlightenment Enlightenment, enlighten or enlightened may refer to: Age of Enlightenment * ...

John Locke
, for instance, described his efforts in ''
Essay Concerning Human Understanding ''An Essay Concerning Human Understanding'' is a work by John Locke John Locke (; 29 August 1632 – 28 October 1704) was an English philosopher and physician, widely regarded as one of the most influential of Age of Enlightenmen ...
'' (1689) as an inquiry "into the original, certainty, and extent of human knowledge, together with the grounds and degrees of belief, opinion, and assent". Almost every major historical philosopher has considered questions about what we know and how we know it. Among the
Ancient Greek philosophers Ancient Greek philosophy arose in the 6th century BC, at a time when the inhabitants of ancient Greece were struggling to repel devastating invasions from the east. Greek philosophy continued throughout the Hellenistic period The Hellenistic p ...
,
Plato Plato ( ; grc-gre, Πλάτων ; 428/427 or 424/423 – 348/347 BC) was an Classical Athens, Athenian philosopher during the Classical Greece, Classical period in Ancient Greece, founder of the Platonist school of thought and the Platoni ...

Plato
distinguished between inquiry regarding what we know and inquiry regarding what exists, particularly in the ''
Republic A republic () is a form of government A government is the system or group of people governing an organized community, generally a state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a month ...
'', the '' Theaetetus'', and the ''
Meno ''Meno'' (; grc-gre, wikt:Μένων, Μένων, ''Ménōn'') is a Socratic dialogue by Plato. Meno begins the dialogue by asking Socrates whether virtue is taught, acquired by practice, or comes by nature. In order to determine whether virt ...

Meno
''. A number of important epistemological concerns also appeared in the works of
Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher A philosopher is someone who practices philosophy Philosophy (from , ) is the study of general and fundamental questio ...

Aristotle
. During the subsequent
Hellenistic period The Hellenistic period spans the period of History of the Mediterranean region, Mediterranean history between the death of Alexander the Great in 323 BC and the emergence of the Roman Empire, as signified by the Battle of Actium in 31  ...
, philosophical schools began to appear which had a greater focus on epistemological questions, often in the form of
philosophical skepticism Philosophical skepticism (American and British English spelling differences, UK spelling: scepticism; from Ancient Greek, Greek σκέψις ''skepsis'', "inquiry") is a family of Philosophy, philosophical views that question the possibility o ...
. For instance, the Pyrrhonian skepticism of
Pyrrho Pyrrho of Elis (; grc, Πύρρων ὁ Ἠλεῖος, Pyrrhо̄n ho Ēleios; ), born in , , was a Greek of , credited as being the first Greek and founder of . Life Pyrrho of Elis is estimated to have lived from around 365/360 until 275 ...
and
Sextus Empiricus Sextus Empiricus ( grc-gre, Σέξτος Ἐμπειρικός; c. 160 – c. 210 AD) was a Ancient Greece, Greek Pyrrhonism, Pyrrhonist philosopher and a physician. His philosophical works are the most complete surviving account of ancient Gree ...
held that
eudaimonia Eudaimonia (Ancient Greek, Greek: :Wiktionary:εὐδαιμονία, εὐδαιμονία ; sometimes anglicized as eudaemonia or eudemonia, ) is a Greek word literally translating to the state or condition of 'good spirit', and which is commonl ...
(flourishing, happiness, or "the good life") could be attained through the application of
epoché Epoché ( ἐποχή ''epokhē'', "cessation") is an ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often rough ...
(suspension of judgment) regarding all non-evident matters. Pyrrhonism was particularly concerned with undermining the epistemological
dogma Dogma is a belief or set of beliefs that is accepted by the members of a group without being questioned or doubted. It may be in the form of an official system of principle, principles or doctrine, doctrines of a religion, such as Catholic Churc ...

dogma
s of
Stoicism Stoicism is a school of Hellenistic philosophy Hellenistic philosophy is the period of Western philosophy Western philosophy encompasses the philosophical Philosophy (from , ) is the study of general and fundamental questions, s ...
and
Epicureanism Epicureanism is a system of founded around 307 BC based upon the teachings of the . Epicureanism was originally a challenge to . Later its main opponent became . Few writings by Epicurus have survived. However, there are independent attestat ...
. The other major school of Hellenistic skepticism was
Academic skepticism Academic skepticism refers to the philosophical skepticism, skeptical period of ancient Platonism dating from around 266 BC, when Arcesilaus became scholarch of the Platonic Academy, until around 90 BC, when Antiochus of Ascalon rejected skepticism ...
, most notably defended by
Carneades Carneades (; el, Καρνεάδης, ''Karneadēs'', "of Carnea Carneia ( grc, Κάρνεια, or grc, Καρνεῖα ''Karneia'', or grc, Κάρνεα ''Karnea'') was the name of one of the tribal traditional festival of Sparta Spar ...

Carneades
and
Arcesilaus Arcesilaus (; grc-gre, Ἀρκεσίλαος; 316/5–241/0 BC) was a Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country ...
, which predominated in the
Platonic Academy The Academy (Ancient Greek Ancient Greek includes the forms of the Greek language Greek ( el, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí Glóssa''), generally referred to by speakers simply as Greek (, ) ...
for almost two centuries. In ancient India the Ajñana school of
ancient Indian philosophy This page lists some links to ancient philosophy, namely philosophical thought extending as far as early post-classical history Post-classical history, as used in world history, generally runs from about 500 AD to 1500 AD (roughly correspond ...
promoted skepticism. Ajñana was a Śramaṇa movement and a major rival of
early Buddhism The term Early Buddhism can refer to two distinct periods, both of which are covered in a separate article: * Pre-sectarian Buddhism, which refers to the teachings and monastic organization and structure, founded by Gautama Buddha The Bu ...
,
Jainism Jainism (), traditionally known as ''Jain Dharma'', is an ancient Indian religion. It is one of the oldest Indian religions. The three main pillars of Jainism are ''Ahimsa in Jainism, ahiṃsā'' (non-violence), ''anekāntavāda'' (non-absolut ...

Jainism
and the Ājīvika school. They held that it was impossible to obtain knowledge of metaphysical nature or ascertain the truth value of philosophical propositions; and even if knowledge was possible, it was useless and disadvantageous for final salvation. They were specialized in refutation without propagating any positive doctrine of their own. After the ancient philosophical era but before the modern philosophical era, a number of
Medieval philosophers In the history of Europe, the Middle Ages or medieval period lasted from the 5th to the late 15th century. It began with the fall of the Western Roman Empire and transitioned into the Renaissance and the Age of Discovery. The Middle Ages i ...
also engaged with epistemological questions at length. Most notable among the Medievals for their contributions to epistemology were
Thomas Aquinas Thomas Aquinas (; it, Tommaso d'Aquino, lit=Thomas of Aquino, Italy, Aquino; 1225 – 7 March 1274) was an Italian Dominican Order, Dominican friar, Philosophy, philosopher, Catholic priest, and Doctor of the Church. An immensely influential ...

Thomas Aquinas
,
John Duns Scotus John Duns ( – 8 November 1308), commonly called Duns Scotus ( ; ; "Duns the Scot"), was a Scottish Catholic priest and Franciscan friar The Franciscans are a group of related Mendicant orders, mendicant Christianity, Christian Cath ...

John Duns Scotus
, and
William of Ockham William of Ockham (; also Occam, from la, Gulielmus Occamus; 1287 – 10 April 1347) was an English Franciscan friar The Franciscans are a group of related Mendicant orders, mendicant Christianity, Christian Catholic religious order, relig ...

William of Ockham
. In the Islamic epistemology
Islamic Golden Age The Islamic Golden Age was a period of cultural, economic, and scientific flourishing in the history of Islam The history of Islam concerns the political, social, economic, and cultural developments of Muslim world, Islamic civilization. M ...
which was booming prior to the Age of Enlightenment in Europe. One of the most prominent and influential philosophers, theologians, jurists, logicians and mystics Abu Hamid
Al-Ghazali Al-Ghazali (, ; full name or , ; Latinized Algazelus or Algazel; – 19 December 1111) was a Persian Persian may refer to: * People and things from Iran, historically called ''Persia'' in the English language ** Persians, Persian people, the ...

Al-Ghazali
wrote over 70 books, including his best-known work in 1107 CE, his spiritual autobiography, "Deliverance from Error" (Al-Munqidh min al-Dalal). In this book Al-Ghazali was seeking to know what we can be certain about: what is true knowledge and not just opinion? To accomplish this goal, he would first consider what kinds of things we can know. This involves a study of epistemology, the theory of knowledge. Epistemology largely came to the fore in philosophy during the
early modern period The early modern period of modern history Human history, or world history, is the narrative of Human, humanity's past. It is understood through archaeology, anthropology, genetics, and linguistics, and since the History of writing, adve ...
, which historians of philosophy traditionally divide up into a dispute between
empiricists In philosophy Philosophy (from , ) is the study of general and fundamental questions, such as those about reason, Metaphysics, existence, Epistemology, knowledge, Ethics, values, Philosophy of mind, mind, and Philosophy of language, ...
(including
Francis Bacon Francis Bacon, 1st Viscount St Alban, (; 22 January 1561 – 9 April 1626), also known as Lord Verulam, was an English philosopher and statesman who served as Attorney General for England and Wales, Attorney General and as Lord Chancellor of K ...

Francis Bacon
,
John Locke John Locke (; 29 August 1632 – 28 October 1704) was an English philosopher and physician, widely regarded as one of the most influential of Enlightenment Enlightenment, enlighten or enlightened may refer to: Age of Enlightenment * ...

John Locke
,
David Hume David Hume (; born David Home; 7 May 1711 NS (26 April 1711 OS) – 25 August 1776) Cranston, Maurice, and Thomas Edmund Jessop. 2020 999999 or triple nine most often refers to: * 999 (emergency telephone number) 250px, A sign on a beach ...

David Hume
, and
George Berkeley George Berkeley (; 12 March 168514 January 1753) – known as Bishop Berkeley (Bishop of Cloyne The Bishop of Cloyne is an episcopal title that takes its name after the small town of Cloyne in County Cork, Republic of Ireland Irela ...

George Berkeley
) and
rationalists In philosophy Philosophy (from , ) is the study of general and fundamental questions, such as those about reason, Metaphysics, existence, Epistemology, knowledge, Ethics, values, Philosophy of mind, mind, and Philosophy of language, ...
(including
René Descartes René Descartes ( or ; ; Latinized Latinisation or Latinization can refer to: * Latinisation of names, the practice of rendering a non-Latin name in a Latin style * Latinisation in the Soviet Union, the campaign in the USSR during the 1920s ...

René Descartes
,
Baruch Spinoza Baruch (de) Spinoza (; ; ; born Baruch Espinosa; later as an author and a correspondent Benedictus de Spinoza, anglicized to Benedict de Spinoza; 24 November 1632 – 21 February 1677) was a Dutch philosopher of Spanish and Portuguese Jews, Por ...

Baruch Spinoza
, and
Gottfried Leibniz Gottfried Wilhelm (von) Leibniz ; see inscription of the engraving depicted in the " 1666–1676" section. ( – 14 November 1716) was a German polymath A polymath ( el, πολυμαθής, , "having learned much"; la, homo universalis, " ...
). The debate between them has often been framed using the question of whether knowledge comes primarily from
sensory experience The theory of sense data is a view in the philosophy of perception The philosophy of perception is concerned with the nature of perceptual experience and the status of perceptual data, in particular how they relate to beliefs about, or knowledg ...

sensory experience
(empiricism), or whether a significant portion of our knowledge is derived entirely from our faculty of
reason Reason is the capacity of consciously applying logic Logic is an interdisciplinary field which studies truth and reasoning Reason is the capacity of consciously making sense of things, applying logic Logic (from Ancient Greek, Greek ...
(rationalism). According to some scholars, this dispute was resolved in the late 18th century by
Immanuel Kant Immanuel Kant (, , ; 22 April 1724 – 12 February 1804) was a German philosopher A philosopher is someone who practices philosophy Philosophy (from , ) is the study of general and fundamental questions, such as those about r ...

Immanuel Kant
, whose
transcendental idealism Transcendental idealism is a philosophical system founded by German philosopher A philosopher is someone who practices philosophy Philosophy (from , ) is the study of general and fundamental questions, such as those about reason, Meta ...
famously made room for the view that "though all our knowledge begins with experience, it by no means follows that all nowledgearises out of experience".


Contemporary historiography

There are a number of different methods that contemporary scholars use when trying to understand the relationship between past epistemology and contemporary epistemology. One of the most contentious questions is this: "Should we assume that the problems of epistemology are perennial, and that trying to reconstruct and evaluate Plato's or Hume's or Kant's arguments is meaningful for current debates, too?" Similarly, there is also a question of whether contemporary philosophers should aim to ''rationally reconstruct and evaluate'' historical views in epistemology, or to ''merely describe'' them. Barry Stroud claims that doing epistemology competently requires the historical study of past attempts to find philosophical understanding of the nature and scope of human knowledge. He argues that since inquiry may progress over time, we may not realize how different the questions that contemporary epistemologists ask are from questions asked at various different points in the history of philosophy.


Central concepts in epistemology


Knowledge

Nearly all debates in epistemology are in some way related to
knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is something that is truth, true. The usual test for a statement of fact is verifiability—that is whether it can be demonstrated to correspond to e ...
. Most generally, "knowledge" is a familiarity, awareness, or understanding of someone or something, which might include facts (
propositional knowledgeIn epistemology Epistemology (; ) is the Outline of philosophy, branch of philosophy concerned with knowledge. Epistemologists study the nature, origin, and scope of knowledge, epistemic Justification (epistemology), justification, the Reason, ...
), skills (
procedural knowledge Procedural knowledge (also known as knowing-how, and sometimes referred to as practical knowledge, imperative knowledge, or performative knowledge) is the knowledge exercised in the performance of some task. Unlike descriptive knowledgeIn epistemolo ...
), or objects (
acquaintance knowledge In philosophy, a distinction is often made between two different kinds of knowledge: knowledge by acquaintance and knowledge by description. Whereas knowledge by description is something like ordinary propositional knowledge (e.g. "I know that sn ...
). Philosophers tend to draw an important distinction between three different senses of "knowing" something: " knowing that" (knowing the truth of propositions), " knowing how" (understanding how to perform certain actions), and " knowing by acquaintance" (directly perceiving an object, being familiar with it, or otherwise coming into contact with it). Epistemology is primarily concerned with the first of these forms of knowledge, propositional knowledge. All three senses of "knowing" can be seen in our ordinary use of the word. In mathematics, you can know 2 + 2 = 4, but there is also knowing to add two numbers, and knowing a (e.g., knowing other persons, or knowing oneself), (e.g., one's hometown), (e.g., cars), or (e.g., addition). While these distinctions are not explicit in English, they are explicitly made in other languages, including French, Portuguese, Spanish, Romanian, German and Dutch (although some languages related to English have been said to retain these verbs, such as Scots). The theoretical interpretation and significance of these linguistic issues remains controversial. In his paper ''On Denoting'' and his later book ''Problems of Philosophy'',
Bertrand Russell Bertrand Arthur William Russell, 3rd Earl Russell (18 May 1872 – 2 February 1970) was a British polymath A polymath ( el, πολυμαθής, , "having learned much"; la, homo universalis, "universal human") is an individual whose know ...
brought a great deal of attention to the distinction between " knowledge by description" and "
knowledge by acquaintance In philosophy Philosophy (from , ) is the study of general and fundamental questions, such as those about reason, Metaphysics, existence, Epistemology, knowledge, Ethics, values, Philosophy of mind, mind, and Philosophy of language, la ...
".
Gilbert Ryle Gilbert Ryle (1900–1976) was a British philosopher, principally known for his critique of Cartesian dualism, for which he coined the phrase "ghost in the machine." He was a representative of the generation of British ordinary language philosoph ...
is similarly credited with bringing more attention to the distinction between knowing how and knowing that in ''
The Concept of Mind ''The Concept of Mind'' is a 1949 book by philosopher Gilbert Ryle, in which the author argues that "mind" is "a philosophical illusion hailing chiefly from René Descartes René Descartes ( or ; ; Latinized: Renatus Cartesius; 31 March 1 ...
''. In ''Personal Knowledge'',
Michael Polanyi Michael Polanyi (; hu, Polányi Mihály; 11 March 1891 – 22 February 1976) was a Hungarian-British polymath, who made important theoretical contributions to physical chemistry, economics Economics () is the social science that st ...

Michael Polanyi
argues for the epistemological relevance of knowledge how and knowledge that; using the example of the act of balance involved in riding a bicycle, he suggests that the theoretical knowledge of the physics involved in maintaining a state of balance cannot substitute for the practical knowledge of how to ride, and that it is important to understand how both are established and grounded. This position is essentially Ryle's, who argued that a failure to acknowledge the distinction between "knowledge that" and "knowledge how" leads to
infinite regress An infinite regress is an infinite series of entities governed by a recursive principle that determines how each entity in the series depends on or is produced by its predecessor. In the epistemic regress, for example, a belief is justified becaus ...

infinite regress
.


''A priori'' and ''a posteriori'' knowledge

One of the most important distinctions in epistemology is between what can be known ''a priori'' (independently of experience) and what can be known ''a posteriori'' (through experience). The terms originate from the Analytic methods of Aristotle's
Organon The ''Organon'' ( grc, Ὄργανον, meaning "instrument, tool, organ") is the standard collection of Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher A philos ...

Organon
, and may be roughly defined as follows: * ''
A priori ''A priori'' and ''a posteriori'' ('from the earlier' and 'from the later', respectively) are Latin phrases used in philosophy Philosophy (from , ) is the study of general and fundamental questions, such as those about reason, Metaph ...
'' knowledge is knowledge that is known independently of experience (that is, it is non-empirical, or arrived at before experience, usually by reason). It will henceforth be acquired through anything that is independent from experience. * ''
A posteriori ''A priori'' and ''a posteriori'' ('from the earlier' and 'from the later', respectively) are Latin phrases used in philosophy Philosophy (from , ) is the study of general and fundamental questions, such as those about reason, Metaph ...
'' knowledge is knowledge that is known by experience (that is, it is empirical, or arrived at through experience). Views that emphasize the importance of ''a priori'' knowledge are generally classified as rationalist. Views that emphasize the importance of ''a posteriori'' knowledge are generally classified as
empiricist In philosophy Philosophy (from , ) is the study of general and fundamental questions, such as those about reason, Metaphysics, existence, Epistemology, knowledge, Ethics, values, Philosophy of mind, mind, and Philosophy of language, ...
.


Belief

One of the core concepts in epistemology is ''belief''. A belief is an attitude that a person holds regarding anything that they take to be true. For instance, to believe that snow is white is comparable to accepting the truth of the
proposition In logic Logic is an interdisciplinary field which studies truth and reasoning Reason is the capacity of consciously making sense of things, applying logic Logic (from Ancient Greek, Greek: grc, wikt:λογική, λογική, lab ...
"snow is white". Beliefs can be ''occurrent'' (e.g. a person actively thinking "snow is white"), or they can be ''dispositional'' (e.g. a person who if asked about the color of snow would assert "snow is white"). While there is not universal agreement about the nature of belief, most contemporary philosophers hold the view that a disposition to express belief ''B'' qualifies as holding the belief ''B''. There are various different ways that contemporary philosophers have tried to describe beliefs, including as representations of ways that the world could be (
Jerry Fodor Jerry Alan Fodor (; April 22, 1935 – November 29, 2017) was an American American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the United States The United States of Ameri ...

Jerry Fodor
), as dispositions to act as if certain things are true (
Roderick Chisholm Roderick Milton Chisholm (; November 27, 1916 – January 19, 1999) was an American philosopher known for his work on epistemology Epistemology (; ) is the Outline of philosophy, branch of philosophy concerned with knowledge. Epistemologist ...
), as interpretive schemes for making sense of someone's actions (
Daniel Dennett Daniel Clement Dennett III (born March 28, 1942) is an American philosopher A philosopher is someone who practices philosophy. The term ''philosopher'' comes from the grc, φιλόσοφος, , translit=philosophos, meaning 'lover of wisdom' ...

Daniel Dennett
and Donald Davidson), or as mental states that fill a particular function (
Hilary Putnam Hilary Whitehall Putnam (; July 31, 1926 – March 13, 2016) was an American philosopher A philosopher is someone who practices philosophy. The term ''philosopher'' comes from the grc, φιλόσοφος, , translit=philosophos, meaning 'love ...

Hilary Putnam
). Some have also attempted to offer significant revisions to our notion of belief, including eliminativists about belief who argue that there is no phenomenon in the natural world which corresponds to our folk psychological concept of belief (
Paul Churchland Paul Montgomery Churchland (born October 21, 1942) is a Canadian philosopher known for his studies in neurophilosophy Neurophilosophy or philosophy of neuroscience is the interdisciplinary study of neuroscience Neuroscience (or neurobiology) ...
) and formal epistemologists who aim to replace our bivalent notion of belief ("either I have a belief or I don't have a belief") with the more permissive, probabilistic notion of credence ("there is an entire spectrum of degrees of belief, not a simple dichotomy between belief and non-belief"). While belief plays a significant role in epistemological debates surrounding knowledge and justification, it also has many other philosophical debates in its own right. Notable debates include: "What is the rational way to revise one's beliefs when presented with various sorts of evidence?"; "Is the content of our beliefs entirely determined by our mental states, or do the relevant facts have any bearing on our beliefs (e.g. if I believe that I'm holding a glass of water, is the non-mental fact that water is H2O part of the content of that belief)?"; "How fine-grained or coarse-grained are our beliefs?"; and "Must it be possible for a belief to be expressible in language, or are there non-linguistic beliefs?"


Truth

Truth Truth is the property of being in accord with fact A fact is something that is true True most commonly refers to truth Truth is the property of being in accord with fact or reality.Merriam-Webster's Online Dictionarytruth 2005 In ...

Truth
is the property or state of being in accordance with facts or reality. On most views, truth is the correspondence of language or thought to a mind-independent world. This is called the
correspondence theory of truth In metaphysics Metaphysics is the branch of philosophy Philosophy (from , ) is the study of general and fundamental questions, such as those about reason, Metaphysics, existence, Epistemology, knowledge, Ethics, values, Philosophy of ...
. Among philosophers who think that it is possible to analyze the conditions necessary for knowledge, virtually all of them accept that truth is such a condition. There is much less agreement about the extent to which a knower must know ''why'' something is true in order to know. On such views, something being known implies that it is true. However, this should not be confused for the more contentious view that one must know that one knows in order to know (the KK principle). Epistemologists disagree about whether belief is the only
truth-bearer A truth-bearer is an entity Entity may refer to: Computing * Character entity reference, replacement text for a character in HTML or XML * Entity class, a thing of interest within an entity–relationship model or diagram * SGML entity, a prim ...
. Other common suggestions for things that can bear the property of being true include
propositions In logic and linguistics, a proposition is the meaning of a declarative sentence (linguistics), sentence. In philosophy, "Meaning (philosophy), meaning" is understood to be a non-linguistic entity which is shared by all sentences with the same mea ...
,
sentence Sentence(s) or The Sentence may refer to: Common uses * Sentence (law), the punishment a judge gives to a defendant found guilty of a crime * Sentence (linguistics), a grammatical unit of language * Sentence (mathematical logic), a formula not cont ...
s,
thought In their most common sense, the terms thought and thinking refer to conscious cognitive processes that can happen independently of sensory stimulation. Their most paradigmatic forms are judging, reasoning, concept formation, problem solving, an ...

thought
s,
utterance In spoken language A spoken language is a language A language is a structured system of communication used by humans, including speech (spoken language), gestures (Signed language, sign language) and writing. Most languages have a writing sy ...

utterance
s, and
judgment Judgement (or US spelling judgment) is also known as ''adjudication Adjudication is the legal process by which an arbitration, arbiter or judge reviews evidence (law), evidence and argumentation, including legal reasoning set forth by opposing ...
s. Plato, in his
Gorgias Gorgias; (483–375 BC) was an ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the f ...
, argues that belief is the most commonly invoked truth-bearer. Many of the debates regarding truth are at the crossroads of epistemology and
logic Logic is an interdisciplinary field which studies truth and reasoning. Informal logic seeks to characterize Validity (logic), valid arguments informally, for instance by listing varieties of fallacies. Formal logic represents statements and ar ...

logic
. Some contemporary debates regarding truth include: How do we define truth? Is it even possible to give an informative definition of truth? What things are truth-bearers and are therefore capable of being true or false? Are truth and falsity
bivalentBivalent may refer to: * Bivalent (chemistry), a molecule formed from two or more atoms bound together *Bivalent (engine), an engine that can operate on two different types of fuel *Bivalent (genetics), a pair of homologous chromosomes *Bivalent logi ...
, or are there other truth values? What are the
criteria of truth In epistemology Epistemology (; ) is the Outline of philosophy, branch of philosophy concerned with knowledge. Epistemologists study the nature, origin, and scope of knowledge, epistemic Justification (epistemology), justification, the Reaso ...
that allow us to identify it and to distinguish it from falsity? What role does truth play in constituting
knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is something that is truth, true. The usual test for a statement of fact is verifiability—that is whether it can be demonstrated to correspond to e ...
? And is truth
absoluteAbsolute may refer to: Companies * Absolute Entertainment, a video game publisher * Absolute Radio, (formerly Virgin Radio), independent national radio station in the UK * Absolute Software Corporation, specializes in security and data risk managem ...
, or is it merely
relative Relative may refer to: General use *Kinship and family, the principle binding the most basic social units society. If two people are connected by circumstances of birth, they are said to be ''relatives'' Philosophy *Relativism, the concept that p ...
to one's perspective?


Justification

As the term "justification" is used in epistemology, a belief is justified if one has good reason for holding it. Loosely speaking, justification is the ''reason'' that someone holds a rationally admissible belief, on the assumption that it is a ''good reason'' for holding it. Sources of justification might include (the evidence of the senses),
reason Reason is the capacity of consciously applying logic Logic is an interdisciplinary field which studies truth and reasoning Reason is the capacity of consciously making sense of things, applying logic Logic (from Ancient Greek, Greek ...
, and authoritative
testimony In law and in religion, testimony is a solemn attestation as to the truth of a matter. Etymology The words "testimony" and "testify" both derive from the Latin word ''testis'', referring to the notion of a disinterested Third-party source, thir ...
, among others. Importantly however, a belief being justified does ''not'' guarantee that the belief is true, since a person could be justified in forming beliefs based on very convincing evidence that was nonetheless deceiving. In
Plato Plato ( ; grc-gre, Πλάτων ; 428/427 or 424/423 – 348/347 BC) was an Classical Athens, Athenian philosopher during the Classical Greece, Classical period in Ancient Greece, founder of the Platonist school of thought and the Platoni ...

Plato
's '' Theaetetus'',
Socrates Socrates (; ; –399 BC) was a Greek philosopher from Athens Athens ( ; el, Αθήνα, Athína ; grc, Ἀθῆναι, Athênai (pl.) ) is the capital city, capital and List of cities in Greece, largest city of Greece. Athens domi ...

Socrates
considers a number of theories as to what knowledge is, first excluding merely true belief as an adequate account. For example, an ill person with no medical training, but with a generally optimistic attitude, might believe that he will recover from his illness quickly. Nevertheless, even if this belief turned out to be true, the patient would not have ''known'' that he would get well since his belief lacked justification. The last account that Plato considers is that knowledge is true belief "with an account" that explains or defines it in some way. According to
Edmund Gettier Edmund Lee Gettier III (; October 31, 1927 – March 23, 2021) was an American American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the United States The United States of ...
, the view that Plato is describing here is that knowledge is ''justified true belief''. The truth of this view would entail that in order to know that a given proposition is true, one must not only believe the relevant true proposition, but must also have a good reason for doing so. One implication of this would be that no one would gain knowledge just by believing something that happened to be true.
Edmund Gettier Edmund Lee Gettier III (; October 31, 1927 – March 23, 2021) was an American American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the United States The United States of ...
's famous 1963 paper, "Is Justified True Belief Knowledge?", popularized the claim that the definition of knowledge as justified true belief had been widely accepted throughout the history of philosophy.Edmund L. Gettier
"Is Justified True Belief Knowledge?"
''
Analysis Analysis is the process of breaking a complex topic or substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a definite chemical composit ...
'', Vol. 23, pp. 121–123 (1963).
The extent to which this is true is highly contentious, since Plato himself disavowed the "justified true belief" view at the end of the ''Theaetetus''. Regardless of the accuracy of the claim, Gettier's paper produced major widespread discussion which completely reoriented epistemology in the second half of the 20th century, with a newfound focus on trying to provide an airtight definition of knowledge by adjusting or replacing the "justified true belief" view. Today there is still little consensus about whether any set of conditions succeeds in providing a set of necessary and sufficient conditions for knowledge, and many contemporary epistemologists have come to the conclusion that no such exception-free definition is possible. However, even if justification fails as a condition for knowledge as some philosophers claim, the question of whether or not a person has good reasons for holding a particular belief in a particular set of circumstances remains a topic of interest to contemporary epistemology and is unavoidably linked to questions about
rationality Rationality is the quality or state of being rational – that is, being based on or agreeable to reason Reason is the capacity of consciously applying logic Logic is an interdisciplinary field which studies truth and reasoning Reaso ...

rationality
.


Internalism and externalism

A central debate about the nature of justification is a debate between epistemological externalists on the one hand and epistemological internalists on the other. While epistemic externalism first arose in attempts to overcome the Gettier problem, it has flourished in the time since as an alternative way of conceiving of epistemic justification. The initial development of epistemic externalism is often attributed to
Alvin Goldman Alvin Ira Goldman (born 1938) is an American philosopher, who is Emeritus Board of Governors Professor of Philosophy and Cognitive Science at Rutgers University in New Jersey and a leading figure in epistemology. Education and career Goldman ear ...
, although numerous other philosophers have worked on the topic in the time since. Externalists hold that factors deemed "external", meaning outside of the psychological states of those who gain knowledge, can be conditions of justification. For example, an externalist response to the Gettier problem is to say that for a justified true belief to count as knowledge, there must be a link or dependency between the belief and the state of the external world. Usually, this is understood to be a causal link. Such causation, to the extent that it is "outside" the mind, would count as an external, knowledge-yielding condition. Internalists, on the other hand, assert that all knowledge-yielding conditions are within the psychological states of those who gain knowledge. Though unfamiliar with the internalist/externalist debate himself, many point to
René Descartes René Descartes ( or ; ; Latinized Latinisation or Latinization can refer to: * Latinisation of names, the practice of rendering a non-Latin name in a Latin style * Latinisation in the Soviet Union, the campaign in the USSR during the 1920s ...

René Descartes
as an early example of the internalist path to justification. He wrote that because the only method by which we perceive the external world is through our senses, and that, because the senses are not infallible, we should not consider our concept of knowledge infallible. The only way to find anything that could be described as "indubitably true", he advocates, would be to see things "clearly and distinctly". He argued that if there is an omnipotent, good being who made the world, then it's reasonable to believe that people are made with the ability to know. However, this does not mean that man's ability to know is perfect. God gave man the ability to know but not with omniscience. Descartes said that man must use his capacities for knowledge correctly and carefully through methodological doubt. The dictum "Cogito ergo sum" (I think, therefore I am) is also commonly associated with Descartes' theory. In his own methodological doubt—doubting everything he previously knew so he could start from a blank slate—the first thing that he could not logically bring himself to doubt was his own existence: "I do not exist" would be a contradiction in terms. The act of saying that one does not exist assumes that someone must be making the statement in the first place. Descartes could doubt his senses, his body, and the world around him—but he could not deny his own existence, because he was able to doubt and must exist to manifest that doubt. Even if some "evil genius" were deceiving him, he would have to exist to be deceived. This one sure point provided him with what he called his Archimedean point, in order to further develop his foundation for knowledge. Simply put, Descartes' epistemological justification depended on his indubitable belief in his own existence and his clear and distinct knowledge of God.


Defining knowledge


The Gettier problem

Edmund Gettier Edmund Lee Gettier III (; October 31, 1927 – March 23, 2021) was an American American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the United States The United States of ...
is best known for his 1963 paper entitled "Is Justified True Belief Knowledge?", which called into question the common conception of knowledge as justified true belief. In just two and a half pages, Gettier argued that there are situations in which one's belief may be justified and true, yet fail to count as knowledge. That is, Gettier contended that while justified belief in a true proposition is necessary for that proposition to be known, it is not sufficient. According to Gettier, there are certain circumstances in which one does not have knowledge, even when all of the above conditions are met. Gettier proposed two
thought experiment A thought experiment is a hypothetical situation in which a hypothesis A hypothesis (plural hypotheses) is a proposed explanation for a phenomenon. For a hypothesis to be a scientific hypothesis, the scientific method requires that one can t ...
s, which have become known as ''Gettier cases'', as
counterexample In logic Logic (from Ancient Greek, Greek: grc, wikt:λογική, λογική, label=none, lit=possessed of reason, intellectual, dialectical, argumentative, translit=logikḗ)Also related to (''logos''), "word, thought, idea, argument, a ...
s to the classical account of knowledge. One of the cases involves two men, Smith and Jones, who are awaiting the results of their applications for the same job. Each man has ten coins in his pocket. Smith has excellent reasons to believe that Jones will get the job (the head of the company told him); and furthermore, Smith knows that Jones has ten coins in his pocket (he recently counted them). From this Smith infers: "The man who will get the job has ten coins in his pocket." However, Smith is unaware that he ''also'' has ten coins in his own pocket. Furthermore, it turns out that Smith, not Jones, is going to get the job. While Smith has strong evidence to believe that Jones will get the job, he is wrong. Smith therefore has a justified true belief that the man who will get the job has ten coins in his pocket; however, according to Gettier, Smith does not ''know'' that the man who will get the job has ten coins in his pocket, because Smith's belief is "...true by virtue of the number of coins in ''Jones's'' pocket, while Smith does not know how many coins are in Smith's pocket, and bases his belief... on a count of the coins in Jones's pocket, whom he falsely believes to be the man who will get the job." These cases fail to be knowledge because the subject's belief is justified, but only happens to be true by virtue of luck. In other words, he made the correct choice (believing that the man who will get the job has ten coins in his pocket) for the wrong reasons. Gettier then goes on to offer a second similar case, providing the means by which the specifics of his examples can be generalized into a broader problem for defining knowledge in terms of justified true belief. There have been various notable responses to the Gettier problem. Typically, they have involved substantial attempts to provide a new definition of knowledge that is not susceptible to Gettier-style objections, either by providing an additional fourth condition that justified true beliefs must meet to constitute knowledge, or proposing a completely new set of
necessary and sufficient conditions In logic Logic (from Ancient Greek, Greek: grc, wikt:λογική, λογική, label=none, lit=possessed of reason, intellectual, dialectical, argumentative, translit=logikḗ)Also related to (''logos''), "word, thought, idea, argument, ac ...
for knowledge. While there have been far too many published responses for all of them to be mentioned, some of the most notable responses are discussed below.


"No false premises" response

One of the earliest suggested replies to Gettier, and perhaps the most intuitive ways to respond to the Gettier problem, is the "no false premises" response, sometimes also called the "no false lemmas" response. Most notably, this reply was defended by
David Malet Armstrong David Malet Armstrong (8 July 1926 – 13 May 2014), often D. M. Armstrong, was an Australian philosopher. He is well known for his work on metaphysics and the philosophy of mind, and for his defence of a factualist ontology, a Functionalism ...
in his 1973 book, ''Belief, Truth, and Knowledge''. The basic form of the response is to assert that the person who holds the justified true belief (for instance, Smith in Gettier's first case) made the mistake of inferring a true belief (e.g. "The person who will get the job has ten coins in his pocket") from a false belief (e.g. "Jones will get the job"). Proponents of this response therefore propose that we add a fourth necessary and sufficient condition for knowledge, namely, "the justified true belief must not have been inferred from a false belief". This reply to the Gettier problem is simple, direct, and appears to isolate what goes wrong in forming the relevant beliefs in Gettier cases. However, the general consensus is that it fails. This is because while the original formulation by Gettier includes a person who infers a true belief from a false belief, there are many alternate formulations in which this is not the case. Take, for instance, a case where an observer sees what appears to be a dog walking through a park and forms the belief "There is a dog in the park". In fact, it turns out that the observer is not looking at a dog at all, but rather a very lifelike robotic facsimile of a dog. However, unbeknownst to the observer, there ''is'' in fact a dog in the park, albeit one standing behind the robotic facsimile of a dog. Since the belief "There is a dog in the park" does not involve a faulty inference, but is instead formed as the result of misleading perceptual information, there is no inference made from a false premise. It therefore seems that while the observer does in fact have a true belief that her perceptual experience provides justification for holding, she does not actually ''know'' that there is a dog in the park. Instead, she just seems to have formed a "lucky" justified true belief.


Reliabilist response

Reliabilism has been a significant line of response to the Gettier problem among philosophers, originating with work by
Alvin Goldman Alvin Ira Goldman (born 1938) is an American philosopher, who is Emeritus Board of Governors Professor of Philosophy and Cognitive Science at Rutgers University in New Jersey and a leading figure in epistemology. Education and career Goldman ear ...
in the 1960s. According to reliabilism, a belief is justified (or otherwise supported in such a way as to count towards knowledge) only if it is produced by processes that typically yield a sufficiently high ratio of true to false beliefs. In other words, this theory states that a true belief counts as knowledge only if it is produced by a reliable belief-forming process. Examples of reliable processes include standard perceptual processes, remembering, good reasoning, and introspection. One commonly discussed challenge for reliabilism is the case of Henry and the barn façades. In this thought experiment, a man, Henry, is driving along and sees a number of buildings that resemble barns. Based on his perception of one of these, he concludes that he is looking at a barn. While he is indeed looking at a barn, it turns out that all of the other barn-like buildings he saw were façades. According to the challenge, Henry does not ''know'' that he has seen a barn, despite his belief being true, and despite his belief having been formed on the basis of a reliable process (i.e. his vision), since he only acquired his reliably formed true belief by accident. In other words, since he could have just as easily been looking at a barn façade and formed a false belief, the reliability of perception in general does not mean that his belief wasn't merely formed luckily, and this luck seems to preclude him from knowledge.


Infallibilist response

One less common response to the Gettier problem is defended by
Richard Kirkham Richard Ladd Kirkham (born June 18, 1955) is an American American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the United States The United States of America (USA), common ...
, who has argued that the only definition of knowledge that could ever be immune to all counterexamples is the infallibilist definition. To qualify as an item of knowledge, goes the theory, a belief must not only be true and justified, the justification of the belief must ''necessitate'' its truth. In other words, the justification for the belief must be infallible. While infallibilism is indeed an internally coherent response to the Gettier problem, it is incompatible with our everyday knowledge ascriptions. For instance, as the Cartesian skeptic will point out, all of my perceptual experiences are compatible with a skeptical scenario in which I am completely deceived about the existence of the external world, in which case most (if not all) of my beliefs would be false. The typical conclusion to draw from this is that it is possible to doubt most (if not all) of my everyday beliefs, meaning that if I am indeed justified in holding those beliefs, that justification is ''not'' infallible. For the justification to be infallible, my reasons for holding my everyday beliefs would need to completely exclude the possibility that those beliefs were false. Consequently, if a belief must be infallibly justified in order to constitute knowledge, then it must be the case that we are mistaken in most (if not all) instances in which we claim to have knowledge in everyday situations. While it is indeed possible to bite the bullet and accept this conclusion, most philosophers find it implausible to suggest that we know nothing or almost nothing, and therefore reject the infallibilist response as collapsing into
radical skepticism Radical skepticism (or radical scepticism in British English British English (BrE) is the standard dialect of the English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxo ...
.


Indefeasibility condition

Another possible candidate for the fourth condition of knowledge is ''indefeasibility''. Defeasibility theory maintains that there should be no overriding or defeating truths for the reasons that justify one's belief. For example, suppose that person ''S'' believes he saw Tom Grabit steal a book from the library and uses this to justify the claim that Tom Grabit stole a book from the library. A possible defeater or overriding proposition for such a claim could be a true proposition like, "Tom Grabit's identical twin Sam is currently in the same town as Tom." When no defeaters of one's justification exist, a subject would be epistemologically justified. In a similar vein, the Indian philosopher B.K. Matilal drew on the
Navya-Nyāya The Navya-Nyāya or Neo-Logical ''darśana ''Darśana'' (Sanskrit Sanskrit (, attributively , ''saṃskṛta-'', nominalization, nominally , ''saṃskṛtam'') is a classical language of South Asia belonging to the Indo-Aryan languages, In ...
fallibilist tradition to respond to the Gettier problem. Nyaya theory distinguishes between ''know p'' and ''know that one knows p''—these are different events, with different causal conditions. The second level is a sort of implicit inference that usually follows immediately the episode of knowing p (knowledge ''simpliciter''). The Gettier case is examined by referring to a view of
Gangesha Upadhyaya Gangesha Upadhyaya ( sa, गंगेश उपाध्याय, ''Gaṅgeśa Upādhyāya'') (first half of the 14th century) was an India India (Hindi: ), officially the Republic of India (Hindi: ), is a country in South Asia. It is the ...
(late 12th century), who takes any true belief to be knowledge; thus a true belief acquired through a wrong route may just be regarded as knowledge simpliciter on this view. The question of justification arises only at the second level, when one considers the knowledge-hood of the acquired belief. Initially, there is lack of uncertainty, so it becomes a true belief. But at the very next moment, when the hearer is about to embark upon the venture of ''knowing whether he knows p'', doubts may arise. "If, in some Gettier-like cases, I am wrong in my inference about the knowledge-hood of the given occurrent belief (for the evidence may be pseudo-evidence), then I am mistaken about the truth of my belief—and this is in accordance with Nyaya fallibilism: not all knowledge-claims can be sustained." The Gettier problem is dealt with in Chapter 4, ''Knowledge as a mental episode''. The thread continues in the next chapter ''Knowing that one knows''. It is also discussed in Matilal's ''Word and the World'' p. 71–72.


Tracking condition

Robert Nozick Robert Nozick (; November 16, 1938 – January 23, 2002) was an American philosopher A philosopher is someone who practices philosophy. The term ''philosopher'' comes from the grc, φιλόσοφος, , translit=philosophos, meaning 'lov ...
has offered a definition of knowledge according to which ''S'' knows that ''P'' if and only if: * ''P'' is true; * ''S'' believes that ''P''; * if ''P'' were false, ''S'' would not believe that ''P''; * if ''P'' were true, ''S'' would believe that ''P''. Philosophical Explanations Chapter 3 "Knowledge and Skepticism" I. Knowledge ''Conditions for Knowledge'' pp. 172–178. Nozick argues that the third of these conditions serves to address cases of the sort described by Gettier. Nozick further claims this condition addresses a case of the sort described by D.M. Armstrong: A father believes his daughter is innocent of committing a particular crime, both because of faith in his baby girl and (now) because he has seen presented in the courtroom a conclusive demonstration of his daughter's innocence. His belief via the method of the courtroom satisfies the four subjunctive conditions, but his faith-based belief does not. If his daughter were guilty, he would still believe her innocence, on the basis of faith in his daughter; this would violate the third condition. The British philosopher Simon Blackburn has criticized this formulation by suggesting that we do not want to accept as knowledge beliefs which, while they "track the truth" (as Nozick's account requires), are not held for appropriate reasons. He says that "we do not want to award the title of knowing something to someone who is only meeting the conditions through a defect, flaw, or failure, compared with someone else who is not meeting the conditions." In addition to this, externalist accounts of knowledge, such as Nozick's, are often forced to reject closure in cases where it is intuitively valid. An account similar to Nozick's has also been offered by Fred Dretske, although his view focuses more on relevant alternatives that might have obtained if things had turned out differently. Views of both the Nozick variety and the Dretske variety have faced serious problems suggested by Saul Kripke.


Knowledge-first response

Timothy Williamson has advanced a theory of knowledge according to which knowledge is not justified true belief plus some extra conditions, but primary. In his book ''Knowledge and its Limits'', Williamson argues that the concept of knowledge cannot be broken down into a set of other concepts through analysis—instead, it is ''sui generis''. Thus, according to Williamson, justification, truth, and belief are Necessary and sufficient, necessary but not sufficient for knowledge. Williamson is also known for being one of the only philosophers who take knowledge to be a mental state; most epistemologists assert that belief (as opposed to knowledge) is a mental state. As such, Williamson's claim has been seen to be highly counterintuitive.


Causal theory and naturalized epistemology

In an earlier paper that predates his development of reliabilism,
Alvin Goldman Alvin Ira Goldman (born 1938) is an American philosopher, who is Emeritus Board of Governors Professor of Philosophy and Cognitive Science at Rutgers University in New Jersey and a leading figure in epistemology. Education and career Goldman ear ...
writes in his "Causal Theory of Knowledge, Causal Theory of Knowing" that knowledge requires a Causal chain, causal link between the truth of a proposition and the belief in that proposition. A similar view has also been defended by Hilary Kornblith in ''Knowledge and its Place in Nature'', although his view is meant to capture an empirical scientific conception of knowledge, not an analysis of the everyday concept "knowledge". Kornblith, in turn, takes himself to be elaborating on the naturalized epistemology framework first suggested by W.V.O. Quine.


The value problem

We generally assume that knowledge is more valuable than mere true belief. If so, what is the explanation? A formulation of the value problem in epistemology first occurs in
Plato Plato ( ; grc-gre, Πλάτων ; 428/427 or 424/423 – 348/347 BC) was an Classical Athens, Athenian philosopher during the Classical Greece, Classical period in Ancient Greece, founder of the Platonist school of thought and the Platoni ...

Plato
's Meno. Socrates points out to Meno that a man who knew the way to Larissa could lead others there correctly. But so, too, could a man who had true beliefs about how to get there, even if he had not gone there or had any knowledge of Larissa. Socrates says that it seems that both knowledge and true opinion can guide action. Meno then wonders why knowledge is valued more than true belief and why knowledge and true belief are different. Socrates responds that knowledge is more valuable than mere true belief because it is tethered or justified. Justification, or working out the reason for a true belief, locks down true belief. The problem is to identify what (if anything) makes knowledge more valuable than mere true belief, or that makes knowledge more valuable than a mere minimal conjunction of its components, such as justification, safety, sensitivity, statistical likelihood, and anti-Gettier conditions, on a particular analysis of knowledge that conceives of knowledge as divided into components (to which knowledge-first epistemological theories, which posit knowledge as fundamental, are notable exceptions). The value problem re-emerged in the philosophical literature on epistemology in the twenty-first century following the rise of virtue epistemology in the 1980s, partly because of the obvious link to the concept of value in ethics.


Virtue epistemology

In contemporary philosophy, epistemologists including Ernest Sosa, John Greco (philosopher), John Greco, Jonathan Kvanvig, Linda Trinkaus Zagzebski, Linda Zagzebski, and Duncan Pritchard have defended virtue epistemology as a solution to the value problem. They argue that epistemology should also evaluate the "properties" of people as epistemic agents (i.e. intellectual virtues), rather than merely the properties of propositions and propositional mental attitudes. The value problem has been presented as an argument against epistemic reliabilism by Linda Zagzebski, Wayne Riggs, and Richard Swinburne, among others. Zagzebski analogizes the value of knowledge to the value of espresso produced by an espresso maker: "The liquid in this cup is not improved by the fact that it comes from a reliable espresso maker. If the espresso tastes good, it makes no difference if it comes from an unreliable machine." For Zagzebski, the value of knowledge deflates to the value of mere true belief. She assumes that reliability in itself has no value or disvalue, but Goldman and Olsson disagree. They point out that Zagzebski's conclusion rests on the assumption of veritism: all that matters is the acquisition of true belief. To the contrary, they argue that a reliable process for acquiring a true belief adds value to the mere true belief by making it more likely that future beliefs of a similar kind will be true. By analogy, having a reliable espresso maker that produced a good cup of espresso would be more valuable than having an unreliable one that luckily produced a good cup because the reliable one would more likely produce good future cups compared to the unreliable one. The value problem is important to assessing the adequacy of theories of knowledge that conceive of knowledge as consisting of true belief and other components. According to Jonathan Kvanvig, Kvanvig, an adequate account of knowledge should resist counterexamples and allow an explanation of the value of knowledge over mere true belief. Should a theory of knowledge fail to do so, it would prove inadequate. One of the more influential responses to the problem is that knowledge is not particularly valuable and is not what ought to be the main focus of epistemology. Instead, epistemologists ought to focus on other mental states, such as understanding. Advocates of virtue epistemology have argued that the value of knowledge comes from an internal relationship between the knower and the mental state of believing.


Acquiring knowledge


Sources of knowledge

There are many proposed sources of knowledge and justified belief which we take to be actual sources of knowledge in our everyday lives. Some of the most commonly discussed include
perception Perception (from the Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" o ...

perception
,
reason Reason is the capacity of consciously applying logic Logic is an interdisciplinary field which studies truth and reasoning Reason is the capacity of consciously making sense of things, applying logic Logic (from Ancient Greek, Greek ...
,
memory Memory is the faculty of the brain A brain is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exis ...

memory
, and
testimony In law and in religion, testimony is a solemn attestation as to the truth of a matter. Etymology The words "testimony" and "testify" both derive from the Latin word ''testis'', referring to the notion of a disinterested Third-party source, thir ...

testimony
.


Important distinctions


''A priori''–''a posteriori'' distinction

As mentioned above, epistemologists draw a distinction between what can be known ''A priori and a posteriori, a priori'' (independently of experience) and what can only be known ''A priori and a posteriori, a posteriori'' (through experience). Much of what we call ''a priori'' knowledge is thought to be attained through reason alone, as featured prominently in rationalism. This might also include a non-rational faculty of intuition, as defended by proponents of innatism. In contrast, ''a posteriori'' knowledge is derived entirely through experience or as a result of experience, as emphasized in empiricism. This also includes cases where knowledge can be traced back to an earlier experience, as in memory or testimony. A way to look at the difference between the two is through an example. Bruce Russell gives two propositions in which the reader decides which one he believes more. Option A: All crows are birds. Option B: All crows are black. If you believe option A, then you are a priori justified in believing it because you don't have to see a crow to know it's a bird. If you believe in option B, then you are posteriori justified to believe it because you have seen many crows therefore knowing they are black. He goes on to say that it doesn't matter if the statement is true or not, only that if you believe in one or the other that matters. The idea of ''a priori'' knowledge is that it is based on intuition or rational insights. Laurence BonJour says in his article "The Structure of Empirical Knowledge", that a "rational insight is an immediate, non-inferential grasp, apprehension or 'seeing' that some proposition is necessarily true." (3) Going back to the crow example, by Laurence BonJour's definition the reason you would believe in option A is because you have an immediate knowledge that a crow is a bird, without ever experiencing one. Evolutionary psychology takes a novel approach to the problem. It says that there is an innate predisposition for certain types of learning. "Only small parts of the brain resemble a tabula rasa; this is true even for human beings. The remainder is more like an exposed negative waiting to be dipped into a developer fluid".


Analytic–synthetic distinction

Immanuel Kant Immanuel Kant (, , ; 22 April 1724 – 12 February 1804) was a German philosopher A philosopher is someone who practices philosophy Philosophy (from , ) is the study of general and fundamental questions, such as those about r ...

Immanuel Kant
, in his ''Critique of Pure Reason'', drew a distinction between "analytic" and "synthetic" propositions. He contended that some propositions are such that we can know they are true just by understanding their meaning. For example, consider, "My father's brother is my uncle." We can know it is true solely by virtue of our understanding in what its terms mean. Philosophers call such propositions "analytic". Synthetic propositions, on the other hand, have distinct subjects and predicates. An example would be, "My father's brother has black hair." Kant stated that all mathematical and scientific statements are analytic priori propositions because they are logical truth, necessarily true but our knowledge about the attributes of the mathematical or physical subjects we can only get by logical inference. While this distinction is first and foremost about Meaning (philosophy of language), meaning and is therefore most relevant to the philosophy of language, the distinction has significant epistemological consequences, seen most prominently in the works of the logical positivism, logical positivists. In particular, if the set of propositions which can only be known ''a posteriori'' is coextensive with the set of propositions which are synthetically true, and if the set of propositions which can be known ''a priori'' is coextensive with the set of propositions which are analytically true (or in other words, which are true by definition), then there can only be two kinds of successful inquiry: Logico-mathematical inquiry, which investigates what is true by definition, and empirical inquiry, which investigates what is true in the world. Most notably, this would exclude the possibility that branches of philosophy like
metaphysics Metaphysics is the branch of philosophy that studies the first principles of being, identity and change, space and time, causality, necessity and possibility. It includes questions about the nature of consciousness and the relationship between ...

metaphysics
could ever provide informative accounts of what actually exists. The American philosopher Willard Van Orman Quine, in his paper "Two Dogmas of Empiricism", famously challenged the analytic-synthetic distinction, arguing that the boundary between the two is too blurry to provide a clear division between propositions that are true by definition and propositions that are not. While some contemporary philosophers take themselves to have offered more sustainable accounts of the distinction that are not vulnerable to Quine's objections, there is no consensus about whether or not these succeed.


Science as knowledge acquisition

Science is often considered to be a refined, formalized, systematic, institutionalized form of the pursuit and acquisition of empirical knowledge. As such, the
philosophy of science Philosophy of science is a branch of philosophy concerned with the foundations, methodology, methods, and implications of science. The central questions of this study concern Demarcation problem, what qualifies as science, the reliability of s ...
may be viewed variously as an application of the principles of epistemology or as a foundation for epistemological inquiry.


The regress problem

The Regress argument, regress problem (also known as Agrippa's Trilemma) is the problem of providing a complete logical foundation for human knowledge. The traditional way of supporting a rational argument is to appeal to other rational arguments, typically using chains of reason and rules of logic. A classic example that goes back to Aristotle is deducing that ''Socrates is mortal''. We have a logical rule that says ''All humans are mortal'' and an assertion that ''Socrates is human'' and we deduce that ''Socrates is mortal''. In this example how do we know that Socrates is human? Presumably we apply other rules such as: ''All born from human females are human''. Which then leaves open the question how do we know that all born from humans are human? This is the regress problem: how can we eventually terminate a logical argument with some statements that do not require further justification but can still be considered rational and justified? As John Pollock stated:
... to justify a belief one must appeal to a further justified belief. This means that one of two things can be the case. Either there are some beliefs that we can be justified for holding, without being able to justify them on the basis of any other belief, or else for each justified belief there is an infinite regress of (potential) justification [the nebula theory]. On this theory there is no rock bottom of justification. Justification just meanders in and out through our network of beliefs, stopping nowhere. p. 26.
The apparent impossibility of completing an infinite chain of reasoning is thought by some to support skepticism. It is also the impetus for Descartes' famous dictum: ''I think, therefore I am''. Descartes was looking for some logical statement that could be true without appeal to other statements.


Responses to the regress problem

Many epistemologists studying justification have attempted to argue for various types of chains of reasoning that can escape the regress problem.


Foundationalism

Foundationalism, Foundationalists respond to the regress problem by asserting that certain "foundations" or "basic beliefs" support other beliefs but do not themselves require justification from other beliefs. These beliefs might be justified because they are self-evident, infallible, or derive from reliable cognitive mechanisms. Perception, memory, and a priori intuition are often considered possible examples of basic beliefs. The chief criticism of foundationalism is that if a belief is not supported by other beliefs, accepting it may be arbitrary or unjustified.


Coherentism

Another response to the regress problem is coherentism, which is the rejection of the assumption that the regress proceeds according to a pattern of linear justification. To avoid the charge of circularity, coherentism, coherentists hold that an individual belief is justified circularly by the way it fits together (coheres) with the rest of the belief system of which it is a part. This theory has the advantage of avoiding the infinite regress without claiming special, possibly arbitrary status for some particular class of beliefs. Yet, since a system can be coherent while also being wrong, coherentists face the difficulty of ensuring that the whole system correspondence theory of truth, corresponds to reality. Additionally, most logicians agree that any argument that is circular is, at best, only trivially valid. That is, to be illuminating, arguments must operate with information from multiple premises, not simply conclude by reiterating a premise. Nigel Warburton writes in ''Thinking from A to Z'' that "[c]ircular arguments are not invalid; in other words, from a logical point of view there is nothing intrinsically wrong with them. However, they are, when viciously circular, spectacularly uninformative."


Infinitism

An alternative resolution to the regress problem is known as "infinitism". Infinitists take the infinite series to be merely potential, in the sense that an individual may have indefinitely many reasons available to them, without having consciously thought through all of these reasons when the need arises. This position is motivated in part by the desire to avoid what is seen as the arbitrariness and circularity of its chief competitors, foundationalism and coherentism. The most prominent defense of infinitism has been given by Peter D. Klein, Peter Klein.


Foundherentism

An intermediate position, known as "foundherentism", is advanced by Susan Haack. Foundherentism is meant to unify foundationalism and coherentism. Haack explains the view by using a crossword puzzle as an analogy. Whereas, for example, infinitists regard the regress of reasons as taking the form of a single line that continues indefinitely, Haack has argued that chains of properly justified beliefs look more like a crossword puzzle, with various different lines mutually supporting each other. Thus, Haack's view leaves room for both chains of beliefs that are "vertical" (terminating in foundational beliefs) and chains that are "horizontal" (deriving their justification from coherence with beliefs that are also members of foundationalist chains of belief).


Philosophical skepticism

Philosophical skepticism, Epistemic skepticism questions whether knowledge is possible at all. Generally speaking, skeptics argue that knowledge requires certainty, and that most or all of our beliefs are Fallibilism, fallible (meaning that our grounds for holding them always, or almost always, fall short of certainty), which would together entail that knowledge is always or almost always acatalepsy, impossible for us. Characterizing knowledge as strong or weak is dependent on a person's viewpoint and their characterization of knowledge. Much of modern epistemology is derived from attempts to better understand and address philosophical skepticism.


Pyrrhonism

One of the oldest forms of epistemic skepticism can be found in Agrippa's trilemma (named after the Pyrrhonism, Pyrrhonist philosopher Agrippa the Skeptic) which demonstrates that certainty can not be achieved with regard to beliefs. Pyrrhonism dates back to Pyrrho of Elis from the 4th century BCE, although most of what we know about Pyrrhonism today is from the surviving works of
Sextus Empiricus Sextus Empiricus ( grc-gre, Σέξτος Ἐμπειρικός; c. 160 – c. 210 AD) was a Ancient Greece, Greek Pyrrhonism, Pyrrhonist philosopher and a physician. His philosophical works are the most complete surviving account of ancient Gree ...
. Pyrrhonists claim that for any argument for a non-evident proposition, an equally convincing argument for a contradictory proposition can be produced. Pyrrhonists do not dogmatically deny the possibility of knowledge, but instead point out that beliefs about non-evident matters cannot be substantiated.


Cartesian skepticism

The evil demon, Cartesian evil demon problem, first raised by
René Descartes René Descartes ( or ; ; Latinized Latinisation or Latinization can refer to: * Latinisation of names, the practice of rendering a non-Latin name in a Latin style * Latinisation in the Soviet Union, the campaign in the USSR during the 1920s ...

René Descartes
, supposes that our sensory impressions may be controlled by some external power rather than the result of ordinary veridical perception. In such a scenario, nothing we sense would actually exist, but would instead be mere illusion. As a result, we would never be able to know anything about the world, since we would be systematically deceived about everything. The conclusion often drawn from evil demon skepticism is that even if we are not completely deceived, all of the information provided by our senses is still ''compatible'' with skeptical scenarios in which we are completely deceived, and that we must therefore either be able to exclude the possibility of deception or else must deny the possibility of ''infallible'' knowledge (that is, knowledge which is completely certain) beyond our immediate sensory impressions. While the view that no beliefs are beyond doubt other than our immediate sensory impressions is often ascribed to Descartes, he in fact thought that we ''can'' exclude the possibility that we are systematically deceived, although his reasons for thinking this are based on a highly contentious ontological argument for the existence of a benevolent God who would not allow such deception to occur.


Responses to philosophical skepticism

Epistemological skepticism can be classified as either "mitigated" or "unmitigated" skepticism. Mitigated skepticism rejects "strong" or "strict" knowledge claims but does approve weaker ones, which can be considered "virtual knowledge", but only with regard to justified beliefs. Unmitigated skepticism rejects claims of both virtual and strong knowledge. Characterizing knowledge as strong, weak, virtual or genuine can be determined differently depending on a person's viewpoint as well as their characterization of knowledge. Some of the most notable attempts to respond to unmitigated skepticism include direct realism, disjunctivism, Scottish common sense realism, common sense philosophy, pragmatism, fideism, and fictionalism.


Schools of thought in epistemology


Empiricism

Empiricism is a view in the theory of knowledge which focuses on the role of experience, especially experience based on perception, perceptual observations by the senses, in the generation of knowledge. Certain forms exempt disciplines such as mathematics and
logic Logic is an interdisciplinary field which studies truth and reasoning. Informal logic seeks to characterize Validity (logic), valid arguments informally, for instance by listing varieties of fallacies. Formal logic represents statements and ar ...

logic
from these requirements. There are many variants of empiricism, including British empiricism, Empiricism#Logical empiricism, logical empiricism, phenomenalism, and some versions of Scottish common sense realism, common sense philosophy. Most forms of empiricism give epistemologically privileged status to sensory impressions or sense data, although this plays out very differently in different cases. Some of the most famous historical empiricists include
John Locke John Locke (; 29 August 1632 – 28 October 1704) was an English philosopher and physician, widely regarded as one of the most influential of Enlightenment Enlightenment, enlighten or enlightened may refer to: Age of Enlightenment * ...

John Locke
,
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David Hume
,
George Berkeley George Berkeley (; 12 March 168514 January 1753) – known as Bishop Berkeley (Bishop of Cloyne The Bishop of Cloyne is an episcopal title that takes its name after the small town of Cloyne in County Cork, Republic of Ireland Irela ...

George Berkeley
,
Francis Bacon Francis Bacon, 1st Viscount St Alban, (; 22 January 1561 – 9 April 1626), also known as Lord Verulam, was an English philosopher and statesman who served as Attorney General for England and Wales, Attorney General and as Lord Chancellor of K ...

Francis Bacon
, John Stuart Mill, Rudolf Carnap, and
Bertrand Russell Bertrand Arthur William Russell, 3rd Earl Russell (18 May 1872 – 2 February 1970) was a British polymath A polymath ( el, πολυμαθής, , "having learned much"; la, homo universalis, "universal human") is an individual whose know ...
.


Rationalism

Rationalism is the epistemological view that reason is the chief source of knowledge and the main determinant of what constitutes knowledge. More broadly, it can also refer to any view which appeals to reason as a source of knowledge or justification. Rationalism is one of the two classical views in epistemology, the other being empiricism. Rationalists claim that the mind, through the use of reason, can directly grasp certain truths in various domains, including
logic Logic is an interdisciplinary field which studies truth and reasoning. Informal logic seeks to characterize Validity (logic), valid arguments informally, for instance by listing varieties of fallacies. Formal logic represents statements and ar ...

logic
, mathematics,
ethics Ethics or moral philosophy is a branch of philosophy Philosophy (from , ) is the study of general and fundamental questions, such as those about Metaphysics, existence, reason, Epistemology, knowledge, Ethics, values, Philosophy of mind, ...

ethics
, and
metaphysics Metaphysics is the branch of philosophy that studies the first principles of being, identity and change, space and time, causality, necessity and possibility. It includes questions about the nature of consciousness and the relationship between ...

metaphysics
. Rationalist views can range from modest views in mathematics and logic (such as that of Gottlob Frege) to ambitious metaphysical systems (such as that of
Baruch Spinoza Baruch (de) Spinoza (; ; ; born Baruch Espinosa; later as an author and a correspondent Benedictus de Spinoza, anglicized to Benedict de Spinoza; 24 November 1632 – 21 February 1677) was a Dutch philosopher of Spanish and Portuguese Jews, Por ...

Baruch Spinoza
). Some of the most famous rationalists include
Plato Plato ( ; grc-gre, Πλάτων ; 428/427 or 424/423 – 348/347 BC) was an Classical Athens, Athenian philosopher during the Classical Greece, Classical period in Ancient Greece, founder of the Platonist school of thought and the Platoni ...

Plato
,
René Descartes René Descartes ( or ; ; Latinized Latinisation or Latinization can refer to: * Latinisation of names, the practice of rendering a non-Latin name in a Latin style * Latinisation in the Soviet Union, the campaign in the USSR during the 1920s ...

René Descartes
,
Baruch Spinoza Baruch (de) Spinoza (; ; ; born Baruch Espinosa; later as an author and a correspondent Benedictus de Spinoza, anglicized to Benedict de Spinoza; 24 November 1632 – 21 February 1677) was a Dutch philosopher of Spanish and Portuguese Jews, Por ...

Baruch Spinoza
, and
Gottfried Leibniz Gottfried Wilhelm (von) Leibniz ; see inscription of the engraving depicted in the " 1666–1676" section. ( – 14 November 1716) was a German polymath A polymath ( el, πολυμαθής, , "having learned much"; la, homo universalis, " ...
.


Skepticism

Skepticism is a position that questions the possibility of human knowledge, either in particular domains or on a general level. Skepticism does not refer to any one specific school of philosophy, but is rather a thread that runs through many epistemological debates. Philosophical skepticism#Ancient Greek skepticism, Ancient Greek skepticism began during the Hellenistic philosophy, Hellenistic period in philosophy, which featured both Pyrrhonism (notably defended by
Pyrrho Pyrrho of Elis (; grc, Πύρρων ὁ Ἠλεῖος, Pyrrhо̄n ho Ēleios; ), born in , , was a Greek of , credited as being the first Greek and founder of . Life Pyrrho of Elis is estimated to have lived from around 365/360 until 275 ...
and
Sextus Empiricus Sextus Empiricus ( grc-gre, Σέξτος Ἐμπειρικός; c. 160 – c. 210 AD) was a Ancient Greece, Greek Pyrrhonism, Pyrrhonist philosopher and a physician. His philosophical works are the most complete surviving account of ancient Gree ...
) and
Academic skepticism Academic skepticism refers to the philosophical skepticism, skeptical period of ancient Platonism dating from around 266 BC, when Arcesilaus became scholarch of the Platonic Academy, until around 90 BC, when Antiochus of Ascalon rejected skepticism ...
(notably defended by
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and
Carneades Carneades (; el, Καρνεάδης, ''Karneadēs'', "of Carnea Carneia ( grc, Κάρνεια, or grc, Καρνεῖα ''Karneia'', or grc, Κάρνεα ''Karnea'') was the name of one of the tribal traditional festival of Sparta Spar ...

Carneades
). Among ancient Indian philosophers, skepticism was notably defended by the Ajñana school and in the Buddhist Madhyamika tradition. In modern philosophy,
René Descartes René Descartes ( or ; ; Latinized Latinisation or Latinization can refer to: * Latinisation of names, the practice of rendering a non-Latin name in a Latin style * Latinisation in the Soviet Union, the campaign in the USSR during the 1920s ...

René Descartes
' famous inquiry into mind and body began as an exercise in skepticism, in which he started by trying to doubt all purported cases of knowledge in order to search for something that was known with absolute certainty.


Pragmatism

Pragmatism is a fallibilist epistemology that emphasizes the role of action in knowing. Different interpretations of pragmatism variously emphasize: truth as the final outcome of ideal scientific inquiry and experimentation, truth as closely related to usefulness, experience as transacting with instead of representing nature, and human practices as the foundation of language. Pragmatism's origins are often attributed to Charles Sanders Peirce, William James, and John Dewey. In 1878, Peirce formulated the maxim: "Consider what effects, that might conceivably have practical bearings, we conceive the object of our conception to have. Then, our conception of these effects is the whole of our conception of the object." William James suggested that through a pragmatist epistemology, theories "become instruments, not answers to enigmas in which we can rest". In James's pragmatic method, which he adapted from Peirce, metaphysical disputes can be settled by tracing the practical consequences of the different sides of the argument. If this process does not resolve the dispute, then "the dispute is idle". Contemporary versions of pragmatism have been developed by thinkers such as Richard Rorty and
Hilary Putnam Hilary Whitehall Putnam (; July 31, 1926 – March 13, 2016) was an American philosopher A philosopher is someone who practices philosophy. The term ''philosopher'' comes from the grc, φιλόσοφος, , translit=philosophos, meaning 'love ...

Hilary Putnam
. Rorty proposed that values were historically contingent and dependent upon their utility within a given historical period. Contemporary philosophers working in pragmatism are called neopragmatism, neopragmatists, and also include Nicholas Rescher, Robert Brandom, Susan Haack, and Cornel West.


Naturalized epistemology

In certain respects an intellectual descendant of pragmatism, naturalized epistemology considers the evolutionary role of knowledge for agents living and evolving in the world. It de-emphasizes the questions around justification and truth, and instead asks, empirically, how reliable beliefs are formed and the role that evolution played in the development of such processes. It suggests a more empirical approach to the subject as a whole, leaving behind philosophical definitions and consistency arguments, and instead using psychological methods to study and understand how "knowledge" is actually formed and is used in the natural world. As such, it does not attempt to answer the analytic questions of traditional epistemology, but rather replace them with new empirical ones. Naturalized epistemology was first proposed in "Epistemology Naturalized", a seminal paper by W.V.O. Quine. A less radical view has been defended by Hilary Kornblith in ''Knowledge and its Place in Nature'', in which he seeks to turn epistemology towards empirical investigation without completely abandoning traditional epistemic concepts.


Feminist epistemology

Feminist epistemology is a subfield of epistemology which applies feminist theory to epistemological questions. It began to emerge as a distinct subfield in the 20th century. Prominent feminist epistemologists include Miranda Fricker (who developed the concept of epistemic injustice), Donna Haraway (who first proposed the concept of situated knowledge), Sandra Harding, and Elizabeth S. Anderson, Elizabeth Anderson. Harding proposes that feminist epistemology can be broken into three distinct categories: Feminist empiricism, standpoint epistemology, and postmodern epistemology. Feminist epistemology has also played a significant role in the development of many debates in social epistemology.


Epistemic relativism

Epistemic relativism is the view that what is true, rational, or justified for one person need not be true, rational, or justified for another person. Epistemic relativists therefore assert that while there are ''relative'' facts about truth, rationality, justification, and so on, there is no ''perspective-independent'' fact of the matter. Note that this is distinct from epistemic contextualism, which holds that the ''meaning'' of epistemic terms vary across contexts (e.g. "I know" might mean something different in everyday contexts and skeptical contexts). In contrast, epistemic relativism holds that the relevant ''facts'' vary, not just linguistic meaning. Relativism about truth may also be a form of ontological relativism, insofar as relativists about truth hold that facts about what ''exists'' vary based on perspective.


Epistemic constructivism

Social constructivism, Constructivism is a view in philosophy according to which all "knowledge is a compilation of human-made constructions", "not the neutral discovery of an objective truth". Whereas objectivism is concerned with the "object of our knowledge", constructivism emphasizes "how we construct knowledge". Constructivism proposes new definitions for
knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is something that is truth, true. The usual test for a statement of fact is verifiability—that is whether it can be demonstrated to correspond to e ...
and
truth Truth is the property of being in accord with fact A fact is something that is true True most commonly refers to truth Truth is the property of being in accord with fact or reality.Merriam-Webster's Online Dictionarytruth 2005 In ...

truth
, which emphasize intersubjectivity rather than objectivity, and viability rather than truth. The constructivist point of view is in many ways comparable to certain forms of pragmatism.


Epistemic idealism

Idealism is a broad term referring to both an ontological view about the world being in some sense mind-dependent and a corresponding epistemological view that everything we know can be reduced to mental phenomena. First and foremost, "idealism" is a metaphysical doctrine. As an epistemological doctrine, idealism shares a great deal with both empiricism and rationalism. Some of the most famous empiricists have been classified as idealists (particularly George Berkeley, Berkeley), and yet the subjectivism inherent to idealism also resembles that of René Descartes, Descartes in many respects. Many idealists believe that knowledge is primarily (at least in some areas) acquired by ''a priori'' processes, or that it is innatism, innate—for example, in the form of concepts not derived from experience. The relevant theoretical concepts may purportedly be part of the structure of the human mind (as in Immanuel Kant, Kant's theory of
transcendental idealism Transcendental idealism is a philosophical system founded by German philosopher A philosopher is someone who practices philosophy Philosophy (from , ) is the study of general and fundamental questions, such as those about reason, Meta ...
), or they may be said to exist independently of the mind (as in Plato's theory of Forms). Some of the most famous forms of idealism include
transcendental idealism Transcendental idealism is a philosophical system founded by German philosopher A philosopher is someone who practices philosophy Philosophy (from , ) is the study of general and fundamental questions, such as those about reason, Meta ...
(developed by
Immanuel Kant Immanuel Kant (, , ; 22 April 1724 – 12 February 1804) was a German philosopher A philosopher is someone who practices philosophy Philosophy (from , ) is the study of general and fundamental questions, such as those about r ...

Immanuel Kant
), subjective idealism (developed by
George Berkeley George Berkeley (; 12 March 168514 January 1753) – known as Bishop Berkeley (Bishop of Cloyne The Bishop of Cloyne is an episcopal title that takes its name after the small town of Cloyne in County Cork, Republic of Ireland Irela ...

George Berkeley
), and absolute idealism (developed by Georg Wilhelm Friedrich Hegel and Friedrich Wilhelm Joseph Schelling, Friedrich Schelling).


Bayesian epistemology

Bayesian epistemology is a formal approach to various topics in epistemology that has its roots in Thomas Bayes' work in the field of probability theory. One advantage of its formal method in contrast to traditional epistemology is that its concepts and theorems can be defined with a high degree of precision. It is based on the idea that beliefs can be interpreted as Subjective probability, subjective probabilities. As such, they are subject to the laws of probability theory, which act as the norms of
rationality Rationality is the quality or state of being rational – that is, being based on or agreeable to reason Reason is the capacity of consciously applying logic Logic is an interdisciplinary field which studies truth and reasoning Reaso ...

rationality
. These norms can be divided into static constraints, governing the rationality of beliefs at any moment, and dynamic constraints, governing how rational agents should change their beliefs upon receiving new evidence. The most characteristic Bayesian expression of these principles is found in the form of Dutch books, which illustrate irrationality in agents through a series of bets that lead to a loss for the agent no matter which of the probabilistic events occurs. Bayesians have applied these fundamental principles to various epistemological topics but Bayesianism does not cover all topics of traditional epistemology.


Indian pramana

Indian philosophy, Indian schools of philosophy, such as the Hindu philosophy, Hindu Nyaya and Carvaka schools, and the Jain philosophy, Jain and Buddhist philosophy, Buddhist philosophical schools, developed an epistemological tradition independently of the Western philosophical tradition called "pramana". Pramana can be translated as "instrument of knowledge" and refers to various means or sources of knowledge that Indian philosophers held to be reliable. Each school of Indian philosophy had their own theories about which pramanas were valid means to knowledge and which were unreliable (and why). A Vedas, Vedic text, Taittiriya Aranyaka, Taittirīya Āraṇyaka (c. 9th–6th centuries BCE), lists "four means of attaining correct knowledge": ''smṛti'' ("tradition" or "scripture"), ''pratyakṣa'' ("perception"), ''aitihya'' ("communication by one who is expert", or "tradition"), and ''anumāna'' ("reasoning" or "inference"). In the Indian traditions, the most widely discussed pramanas are: ''Pratyakṣa'' (perception), ''Anumāṇa'' (inference), ''Upamāṇa'' (comparison and analogy), ''Arthāpatti'' (postulation, derivation from circumstances), ''Anupalabdi'' (non-perception, negative/cognitive proof) and ''Śabda'' (word, testimony of past or present reliable experts). While the Nyaya school (beginning with the Nyāya Sūtras of Gotama, between 6th-century BCE and 2nd-century CE) were a proponent of realism and supported four pramanas (perception, inference, comparison/analogy and testimony), the Buddhist epistemologists (Dignaga and Dharmakirti) generally accepted only perception and inference. The Carvaka school of materialists only accepted the pramana of perception, and hence were among the first empiricists in the Indian traditions. Another school, the Ajñana, included notable proponents of
philosophical skepticism Philosophical skepticism (American and British English spelling differences, UK spelling: scepticism; from Ancient Greek, Greek σκέψις ''skepsis'', "inquiry") is a family of Philosophy, philosophical views that question the possibility o ...
. The Buddhist philosophy#Epistemology, theory of knowledge of the Buddha in the early Buddhist texts has been interpreted as a form of pragmatism as well as a form of correspondence theory. Likewise, the Buddhist philosopher Dharmakirti has been interpreted both as holding a form of pragmatism or correspondence theory for his view that what is true is what has effective power (''arthakriya''). The Buddhist Madhyamika school's theory of emptiness (shunyata) meanwhile has been interpreted as a form of
philosophical skepticism Philosophical skepticism (American and British English spelling differences, UK spelling: scepticism; from Ancient Greek, Greek σκέψις ''skepsis'', "inquiry") is a family of Philosophy, philosophical views that question the possibility o ...
. The main contribution to epistemology by the Jains has been their theory of "many sided-ness" or "multi-perspectivism" (Anekantavada), which says that since the world is multifaceted, any single viewpoint is limited (''naya'' – a partial standpoint). This has been interpreted as a kind of pluralism or perspectivism. According to Jain epistemology, none of the pramanas gives absolute or perfect knowledge since they are each limited points of view.


Domains of inquiry in epistemology


Social epistemology

Social epistemology deals with questions about knowledge in contexts where our knowledge attributions cannot be explained by simply examining individuals in isolation from one another, meaning that the scope of our knowledge attributions must be widened to include broader social contexts. It also explores the ways in which interpersonal beliefs can be justified in social contexts. The most common topics discussed in contemporary social epistemology are
testimony In law and in religion, testimony is a solemn attestation as to the truth of a matter. Etymology The words "testimony" and "testify" both derive from the Latin word ''testis'', referring to the notion of a disinterested Third-party source, thir ...
, which deals with the conditions under which a belief "x is true" which resulted from being told "x is true" constitutes knowledge; peer disagreement, which deals with when and how I should revise my beliefs in light of other people holding beliefs that contradict mine; and group epistemology, which deals with what it means to attribute knowledge to groups rather than individuals, and when group knowledge attributions are appropriate.


Formal epistemology

Formal epistemology uses formal tools and methods from decision theory,
logic Logic is an interdisciplinary field which studies truth and reasoning. Informal logic seeks to characterize Validity (logic), valid arguments informally, for instance by listing varieties of fallacies. Formal logic represents statements and ar ...

logic
, probability theory and computability theory to model and reason about issues of epistemological interest. Work in this area spans several academic fields, including philosophy, computer science, economics, and statistics. The focus of formal epistemology has tended to differ somewhat from that of traditional epistemology, with topics like uncertainty, induction, and belief revision garnering more attention than the analysis of knowledge, skepticism, and issues with justification.


Metaepistemology

Metaepistemology is the metaphilosophical study of the philosophical method, methods, aims, and subject matter of epistemology. In general, metaepistemology aims to better understand our first-order epistemological inquiry. Some goals of metaepistemology are identifying inaccurate assumptions made in epistemological debates and determining whether the questions asked in mainline epistemology are the ''right'' epistemological questions to be asking.


See also

* Anekantavada * Epistemological pluralism * Evolutionary epistemology * Feminist epistemology * Knowledge-first epistemology * Moral epistemology * Noology, Noölogy * Reformed epistemology * Self-evidence * Sociology of knowledge * Virtue epistemology * Theory of Knowledge (IB Course)


References


Notes


Citations


Sources

; Works cited * * Alfred Jules Ayer, Ayer, Alfred Jules. 1936. ''Language, Truth, and Logic''. * BonJour, Laurence. 2002. ''Epistemology: Classic Problems and Contemporary Responses''. Lanham, MD: Rowman & Littlefield. * Luc Bovens, Bovens, Luc & Stephan Hartmann, Hartmann, Stephan. 2003. ''Bayesian Epistemology''. Oxford: Oxford University Press. * Panayot Butchvarov, Butchvarov, Panayot. 1970. ''The Concept of Knowledge''. Evanston, Northwestern University Press. * * Cohen, Stewart. 1999. "Contextualism, Skepticism, and Reasons", in Tomberlin 1999. * Jonathan Dancy, Dancy, Jonathan. 1991. ''An Introduction to Contemporary Epistemology'' (Second Edition). John Wiley & Sons. * * DeRose, Keith. 1999.
Contextualism: An Explanation and Defense
, in Greco and Sosa 1999. * René Descartes, Descartes, Rene. 1641. ''Meditations on First Philosophy'' * Feldman, Richard. 1999. "Contextualism and Skepticism", in Tomberlin 1999, pp. 91–114. * Edmund Gettier, Gettier, Edmund. 1963. "Is Justified True Belief Knowledge?", ''Analysis'', Vol. 23, pp. 121–123
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* Greco, J. & Sosa, E. 1999. ''Blackwell Guide to Epistemology'', Blackwell Publishing. * Errol Harris, Harris, Errol E. 1970. ''Hypothesis And Perception'', George Allen and Unwin, London, Reprinted 2002 Routledge, London. * * Hay, Clare. 2008. ''The Theory of Knowledge: A Coursebook'', The Lutterworth Press, Cambridge. * Hawthorne, John. 2005. "The Case for Closure", ''Contemporary Debates in Epistemology'', Peter Sosa and Matthias Steup (ed.): 26–43. * Vincent F. Hendricks, Hendricks, Vincent F. 2006. ''Mainstream and Formal Epistemology'', New York: Cambridge University Press. * Kant, Immanuel. 1781. ''Critique of Pure Reason''. * Keeton, Morris T. 1962. "Empiricism", in ''Dictionary of Philosophy'', Dagobert D. Runes (ed.), Littlefield, Adams, and Company, Totowa, NJ, pp. 89–90. * Richard Kirkham, Kirkham, Richard. 1984. "Does the Gettier Problem Rest on a Mistake?" ''Mind'', 93. * Peter D. Klein, Klein, Peter. 1981. ''Certainty: a Refutation of Skepticism'', Minneapolis, MN: University of Minnesota Press. * Henry E. Kyburg, Jr., Kyburg, H.E. 1961. ''Probability and the Logic of Rational Belief'', Middletown, CT: Wesleyan University Press. * Alfred Korzybski, Korzybski, Alfred. 1994 (1933). ''Science and Sanity: An Introduction to Non-Aristotelian Systems and General Semantics'', Fifth Edition. Ft. Worth, TX: Institute of General Semantics. * * Edgar Morin, Morin, Edgar. 1986. ''La Méthode, Tome 3, La Connaissance de la connaissance'' (Method, 3rd volume : The knowledge of knowledge) * Adam Morton, Morton, Adam. 2002. ''A Guide Through the Theory of Knowledge'' (Third Edition) Oxford: Blackwell Publishing. * Nelson, Quee. 2007. ''The Slightest Philosophy'', Indianapolis, IN: Dog Ear Publishing, 296 pages. * Ilkka Niiniluoto, Niiniluoto, Ilkka. 2002. ''Critical Scientific Realism'', Oxford: Oxford Univ. Press. *
Plato Plato ( ; grc-gre, Πλάτων ; 428/427 or 424/423 – 348/347 BC) was an Classical Athens, Athenian philosopher during the Classical Greece, Classical period in Ancient Greece, founder of the Platonist school of thought and the Platoni ...

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. ''
Meno ''Meno'' (; grc-gre, wikt:Μένων, Μένων, ''Ménōn'') is a Socratic dialogue by Plato. Meno begins the dialogue by asking Socrates whether virtue is taught, acquired by practice, or comes by nature. In order to determine whether virt ...

Meno
''. * Karl Popper, Popper, Karl R. 1972.
Objective Knowledge: An Evolutionary Approach
', Oxford: Oxford Univ. Press. * Preyer, G./Siebelt, F./Ulfig, A. 1994.
Language, Mind and Epistemology
', Dordrecht: Kluwer Academic Publishers. * Bertrand Russell, Russell, Bertrand. 1912. ''The Problems of Philosophy'', New York: Oxford University Press. * Bertrand Russell, Russell, Bertrand. 1940. ''An Inquiry into Meaning and Truth'', Nottingham: Spokesman Books. * George Santayana, Santayana, George. 1923. ''Scepticism and Animal Faith'', New York: Charles Scribner's Sons – London: Constable and Co. * African Spir, Spir, African. 1877. ''Denken und Wirklichkeit: Versuch einer Erneuerung der kritischen Philosophie'' (Thought and Reality: Attempt at a Renewal of Critical Philosophy), (Second Edition) Leipzig: J.G. Findel. * * Steup, Matthias. 2005. "Knowledge and Skepticism", ''Contemporary Debates in Epistemology'', Peter Sosa and Matthias Steup (eds.): 1–13. * Tomberlin, James (ed.). 1999. ''Philosophical Perspectives 13, Epistemology'', Blackwell Publishing. * * Ludwig Wittgenstein, Wittgenstein, Ludwig. 1922. ''Tractatus Logico-Philosophicus'', Frank P. Ramsey and C.K. Ogden (trns.), Dover
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External links

;''Stanford Encyclopedia of Philosophy'' articles * * * * * * * * ;''Internet Encyclopedia of Philosophy'' articles * * * * * * * * * * * * * * * * ;''Encyclopedia Britannica''
Epistemology
by Avrum Stroll and A.P. Martinich ;Other links * Th
London Philosophy Study Guide
offers many suggestions on what to read, depending on the student's familiarity with the subject

*
Knowledge-How
at Philpapers *

– a brief introduction to the topic by Keith DeRose.

by Mathew Toll

an

by Paul Newall at the Galilean Library.

– Marjorie Clay (ed.), an electronic publication from The Council for Philosophical Studies.
An Introduction to Epistemology
by Paul Newall, aimed at beginners. * {{Authority control Epistemology,