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Knowledge can be defined as awareness of facts or as practical skills, and may also refer to familiarity with objects or situations. Knowledge of facts, also called
proposition 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 me ...
al knowledge, is often defined as
true True most commonly refers to truth, the state of being in congruence with fact or reality. True may also refer to: Places * True, West Virginia, an unincorporated community in the United States * True, Wisconsin, a town in the United States * Tr ...
belief A belief is an Attitude (psychology), attitude that something is the case, or that some proposition is truth, true. In epistemology, philosophers use the term "belief" to refer to attitudes about the world which can be either truth value, true o ...
that is distinct from opinion or guesswork by virtue of justification. While there is wide agreement among philosophers that propositional knowledge is a form of true belief, many controversies in philosophy focus on justification: whether it is needed at all, how to understand it, and whether something else besides it is needed. These controversies intensified due to a series of thought experiments by Edmund Gettier and have provoked various alternative definitions. Some of them deny that justification is necessary and replace it, for example, with
reliability Reliability, reliable, or unreliable may refer to: Science, technology, and mathematics Computing * Data reliability (disambiguation), a property of some disk arrays in computer storage * High availability * Reliability (computer networking), a ...
or the manifestation of cognitive virtues. Others contend that justification is needed but formulate additional requirements, for example, that no defeaters of the belief are present or that the person would not have the belief if it was false. Knowledge can be produced in many different ways. The most important source of
empirical knowledge Empirical evidence for a proposition is evidence, i.e. what supports or counters this proposition, that is constituted by or accessible to sense experience or experimental procedure. Empirical evidence is of central importance to the sciences and ...
is
perception Perception () is the organization, identification, and interpretation of sensory information in order to represent and understand the presented information or environment. All perception involves signals that go through the nervous syste ...
, which refers to the usage of the
senses A sense is a biological system A biological system is a complex biological network, network which connects several biologically relevant entities. Biological organization spans several scales and are determined based different structures dep ...
. Many theorists also include
introspection Introspection is the examination of one's own conscious thoughts and feelings. In psychology Psychology is the science, scientific study of mind and behavior. Psychology includes the study of consciousness, conscious and Unconscious m ...
as a source of knowledge, not of external physical objects, but of one's own
mental states A mental state, or a mental property, is a state of mind of a person. Mental states comprise a diverse class, including perception, pain experience, belief, desire, intention, emotion, and memory. There is controversy concerning the exact definitio ...
. Other sources often discussed include
memory Memory is the faculty of the mind by which data or information is Encoding (memory), encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If Foresight (psycholo ...
, rational intuition,
inference Inferences are steps in reasoning, moving from premises to logical consequences; etymologically, the word ''wikt:infer, infer'' means to "carry forward". Inference is theoretically traditionally divided into deductive reasoning, deduction and in ...
, 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 ...
. According to
foundationalism Foundationalism concerns epistemology, philosophical theories of knowledge resting upon non-inferential knowledge, justified belief, or some secure foundation of certainty such as a conclusion inferred from a basis of sound premises.Simon Blackbu ...
, some of these sources are basic in the sense that they can justify beliefs without depending on other mental states. This claim is rejected by coherentists, who contend that a sufficient degree of coherence among all the mental states of the believer is necessary for knowledge. Many different aspects of knowledge are investigated and it plays a role in various disciplines. It is the primary subject of the field of
epistemology Epistemology (; ), or the theory of knowledge, is the branch of philosophy concerned with knowledge. Epistemology is considered a major subfield of philosophy, along with other major subfields such as ethics, logic, and metaphysics. Epis ...
, which studies what we know, how we come to know it, and what it means to know something. The problem of the ''value of knowledge'' concerns the question of why knowledge is more valuable than mere true belief.
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 ...
is the controversial thesis that we lack any form of knowledge or that knowledge is impossible.
Formal epistemology Formal epistemology uses formal methods from decision theory, 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, c ...
studies, among other things, the rules governing how knowledge and related states behave and in what relations they stand to each other.
Science Science is a systematic endeavor that Scientific method, builds and organizes knowledge in the form of Testability, testable explanations and predictions about the universe. Science may be as old as the human species, and some of the earli ...
tries to acquire knowledge using the
scientific method The scientific method is an Empirical evidence, empirical method for acquiring knowledge that has characterized the development of science since at least the 17th century (with notable practitioners in previous centuries; see the article hist ...
, which is based on repeatable
experimentation An experiment is a procedure carried out to support or refute a hypothesis, or determine the efficacy or likelihood of something previously untried. Experiments provide insight into Causality, cause-and-effect by demonstrating what outcome oc ...
,
observation Observation is the active acquisition of information from a primary source. In living beings, observation employs the senses. In science, observation can also involve the perception and recording of data (information), data via the use of scienti ...
, and
measurement Measurement is the quantification (science), quantification of variable and attribute (research), attributes of an object or event, which can be used to compare with other objects or events. In other words, measurement is a process of determi ...
. Many religions hold that humans should seek knowledge and that God or the divine is the source of knowledge.


Definitions

Numerous definitions of knowledge have been suggested. Most definitions of knowledge in
analytic philosophy Analytic philosophy is a Academic discipline, branch and Philosophical tradition, tradition of philosophy using philosophical analysis, analysis, popular in the Western world and particularly the Anglosphere, which began around the turn of the 2 ...
recognize three fundamental types. "Knowledge-that", also called propositional knowledge, can be expressed using that-clauses as in "I know that Dave is at home". "Knowledge-how" ( know-how) expresses practical competence, as in "she knows how to swim". Finally, "
knowledge by acquaintance 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 ...
" refers to a familiarity with the known object based on previous direct
experience Experience refers to Consciousness, conscious events in general, more specifically to perceptions, or to the practical knowledge and familiarity that is produced by these conscious processes. Understood as a conscious event in the widest sense, ex ...
. Most definitions of knowledge in analytic philosophy aim to identify the essential features of propositional knowledge. There is wide, though not universal, agreement among philosophers that knowledge involves a
cognitive Cognition refers to "the mental action or process of acquiring knowledge and understanding through thought, experience, and the senses". It encompasses all aspects of intellectual functions and processes such as: perception Perceptio ...
success or an epistemic contact with
reality Reality is the sum or aggregate of all that is real or existent within a system, as opposed to that which is only Object of the mind, imaginary. The term is also used to refer to the ontological status of things, indicating their existence. In ...
, and that
proposition 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 me ...
al knowledge is a form of true belief. Despite the agreement about the general characteristics of knowledge listed above, many deep disagreements remain regarding its exact definition. These disagreements relate to the goals and methods within epistemology and other fields, or to differences concerning the standards of knowledge that people intend to uphold. Some theorists focus on knowledge's most salient features in their attempt to give a practically useful definition. Others try to provide a theoretically precise definition by listing the conditions that are individually necessary and jointly sufficient. The term "analysis of knowledge" (or equivalently, "conception of knowledge" or "theory of knowledge") is often used for this approach. It can be understood in analogy to how
chemists A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin Medieval Latin was the form of Literary Latin used in Roman Catholic Church, Roman Catholic Western Europe during the Middle Ages. In this region it se ...
analyze a sample by seeking a list of all the chemical elements composing it. An example of this approach is characterizing knowledge as
justified true belief Definitions of knowledge try to determine the Essence, essential features of knowledge. Closely related terms are conception of knowledge, theory of knowledge, and analysis of knowledge. Some general features of knowledge are widely accepted among ...
(JTB), which is seen by many philosophers as the standard definition. Others seek a common core among diverse examples of knowledge, such as Paul Silva's "awareness first" epistemology or Barry Allen's definition of knowledge as "superlative artifactual performance". Methodological differences concern whether researchers base their inquiry on abstract and general intuitions or on concrete and specific cases, referred to as ''methodism'' and ''particularism'', respectively. Another source of disagreement is the role of
ordinary language Ordinary language philosophy (OLP) is a philosophical methodology that sees traditional philosophical problems as rooted in misunderstandings philosophers develop by stipulative definition, distorting or forgetting how words are ordinarily used ...
in one's inquiry: the weight given to how the term "knowledge" is used in everyday discourse. According to
Ludwig Wittgenstein Ludwig Josef Johann Wittgenstein ( ; ; 26 April 1889 – 29 April 1951) was an Austrians, Austrian-British people, British philosopher who worked primarily in logic, the philosophy of mathematics, the philosophy of mind, and the philosophy o ...
, for example, there is no clear-cut definition of knowledge since it is just a cluster of concepts related through
family resemblance Family resemblance (german: Familienähnlichkeit, link=no) is a philosophical idea made popular by Ludwig Wittgenstein, with the best known exposition given in his posthumously published book ''Philosophical Investigations'' (1953). It argues tha ...
. Different conceptions of the standards of knowledge are also responsible for various disagreements. Some epistemologists hold that knowledge demands very high requirements, like
infallibility Infallibility refers to an inability to be wrong. It can be applied within a specific domain, or it can be used as a more general adjective. The term has significance in both epistemology Epistemology (; ), or the theory of knowledge, is ...
, and is therefore quite rare. Others see knowledge as a rather common phenomenon, prevalent in many everyday situations, without excessively high standards. In analytic philosophy, knowledge is usually understood as a mental state possessed by an individual person, but the term is sometimes used to refer to a characteristic of a group of people as group knowledge, social knowledge, or collective knowledge. In a slightly different sense, it can also mean knowledge stored in documents, as in "knowledge housed in the library" or the
knowledge base A knowledge base (KB) is a technology used to store complex structured and unstructured information used by a computer system A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or ...
of an
expert system In artificial intelligence, an expert system is a computer system emulating the decision-making ability of a human expert. Expert systems are designed to solve complex problems by automated reasoning, reasoning through bodies of knowledge, repres ...
.


Justified true belief

Many philosophers define knowledge as ''justified true belief'' (JTB). This definition characterizes knowledge through three essential features: as (1) a
belief A belief is an Attitude (psychology), attitude that something is the case, or that some proposition is truth, true. In epistemology, philosophers use the term "belief" to refer to attitudes about the world which can be either truth value, true o ...
that is (2)
true True most commonly refers to truth, the state of being in congruence with fact or reality. True may also refer to: Places * True, West Virginia, an unincorporated community in the United States * True, Wisconsin, a town in the United States * Tr ...
and (3) justified. In the dialogue '' Theaetetus'' by the
ancient Greek philosopher Ancient Greek philosophy arose in the 6th century BC, marking the end of the Greek Dark Ages The term Greek Dark Ages refers to the period of History of Greece, Greek history from the end of the Mycenaean civilization, Mycenaean palatial civi ...
Plato Plato ( ; grc-gre, wikt:Πλάτων, Πλάτων ; 428/427 or 424/423 – 348/347 BC) was a Greeks, Greek philosopher born in Athens during the Classical Greece, Classical period in Ancient Greece. He founded the Platonist school of thou ...
,
Socrates Socrates (; ; –399 BC) was a Greeks, Greek philosopher from Classical Athens, Athens who is credited as the founder of Western philosophy and among the first moral philosophers of the Ethics, ethical tradition of thought. An enigmati ...
pondered the distinction between knowledge and true belief but rejected the JTB definition of knowledge. The most widely accepted feature is truth: one can believe something false but one cannot know something false. A few ordinary language philosophers have raised doubts that knowledge is a form of belief based on everyday expressions like "I do not believe that; I know it". Most theorists reject this distinction and explain such expressions through ambiguities of
natural language In neuropsychology, linguistics, and philosophy of language, a natural language or ordinary language is any language that has linguistic evolution, evolved naturally in humans through use and repetition without conscious planning or premeditati ...
. The main controversy surrounding the JTB definition concerns its third feature: justification. This component is often included because of the impression that some true beliefs are not forms of knowledge. Specifically, this covers cases of
superstition A superstition is any belief or practice considered by non-practitioners to be irrational or supernatural, attributed to fate or magic (supernatural), magic, perceived supernatural influence, or fear of that which is unknown. It is commonly app ...
,
luck Luck is the phenomenon and belief that defines the experience of improbable events, especially improbably positive or negative ones. The Naturalism (philosophy), naturalistic interpretation is that positive and negative events may happen at an ...
y guesses, or erroneous
reasoning Reason is the capacity of Consciousness, consciously applying logic by Logical consequence, drawing conclusions from new or existing information, with the aim of seeking the truth. It is closely associated with such characteristically human activ ...
. The corresponding beliefs may even be true but it seems there is more to knowledge than just being right about something. The JTB definition solves this problem by identifying proper justification as the additional component needed, which is absent in the above-mentioned cases. Many philosophers have understood justification internalistically ('' internalism''): a belief is justified if it is supported by another
mental state A mental state, or a mental property, is a state of mind of a person. Mental states comprise a diverse class, including perception, pain experience, belief, desire, intention, emotion, and memory. There is controversy concerning the exact definitio ...
of the person, such as a perceptual experience, a
memory Memory is the faculty of the mind by which data or information is Encoding (memory), encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If Foresight (psycholo ...
, or a second belief. This mental state has to constitute a sufficiently strong
evidence Evidence for a proposition is what supports this proposition. It is usually understood as an indication that the supported proposition is true. What role evidence plays and how it is conceived varies from field to field. In epistemology, evid ...
or reason for the believed proposition. Some modern versions modify the JTB definition by using an ''externalist'' conception of justification instead. This means that justification depends not just on factors internal to the subject but also on external factors. They can include, for example, that the belief was produced by a reliable process or that the believed fact caused the belief.


Gettier problem and alternatives

The JTB definition came under severe criticism in the 20th century, when Edmund Gettier gave a series of counterexamples. They purport to present concrete cases of justified true beliefs that fail to constitute knowledge. The reason for their failure is usually a form of epistemic luck: the justification is not relevant to the truth. In a well-known example, there is a country road with many barn facades and only one real barn. The person driving is not aware of this, stops by a lucky coincidence in front of the real barn, and forms the belief that he is in front of a barn. It has been argued that this justified true belief does not constitute knowledge since the person wouldn't have been able to tell the difference without the fortuitous accident. So even though the belief is justified, it is a lucky coincidence that it is also true. The responses to these counterexamples have been diverse. According to some, they show that the JTB definition of knowledge is deeply flawed and that a radical reconceptualization of knowledge is necessary, often by denying justification a role. This can happen, for example, by replacing justification with reliability or by understanding knowledge as the manifestation of cognitive virtues. Other approaches include defining it in regard to the cognitive role it plays in providing reasons for doing or thinking something or seeing it as the most general factive mental state operator. Various theorists are diametrically opposed to the radical reconceptualization and either deny that Gettier cases pose problems or they try to solve them by making smaller modifications to how justification is defined. Such approaches result in a minimal modification of the JTB definition. Between these two extremes, some philosophers have suggested various moderate departures. They agree that the JTB definition is a step in the right direction: justified true belief is a necessary condition of knowledge. However, they disagree that it is a sufficient condition. They hold instead that an additional criterion, some feature ''X'', is necessary for knowledge. For this reason, they are often referred to as ''JTB+X'' definitions of knowledge. A closely related approach speaks not of justification but of warrant and defines warrant as justification together with whatever else is necessary to arrive at knowledge. Many candidates for the fourth feature have been suggested. In this regard, knowledge may be defined as justified true belief that does not depend on any false beliefs, that there are no defeaters present, or that the person would not have the belief if it was false. Such and similar definitions are successful at avoiding many of the original Gettier cases. However, they often fall prey to newly conceived counterexamples. To avoid all possible cases, it may be necessary to find a criterion that excludes all forms of epistemic luck. It has been argued that such a criterion would set the required standards of knowledge very high: the belief has to be infallible to succeed in all cases. This would mean that very few of our beliefs amount to knowledge, if any. For example, Richard Kirkham suggests that our definition of knowledge requires that the evidence for the belief necessitates its truth. There is still very little consensus in the academic discourse as to which of the proposed modifications or reconceptualizations is correct.


Types

The English word ''knowledge'' can translate a variety of words in other languages that refer to different states. The Latin words ''cognitio'' and ''scientia'' can both be translated as "knowledge". Romance languages have two major verbs that would both be translated as "to know": for example, ''connaître'' and ''savoir'' in French or ''conocer'' and ''saber'' in Spanish. In ancient Greek, there were four such important knowledge words: '' epistēmē'' (unchanging theoretical knowledge), '' technē'' (expert technical knowledge), '' mētis'' (strategic knowledge), and '' gnōsis'' (personal intellectual knowledge). All these different types of knowledge can be considered forms of cognitive success.


Propositional knowledge

Propositional knowledge, also referred to as
descriptive knowledge In epistemology Epistemology (; ), or the theory of knowledge, is the branch of philosophy concerned with knowledge. Epistemology is considered a major subfield of philosophy, along with other major subfields such as ethics, logic, and m ...
, is the paradigmatic type of knowledge in analytic philosophy, and various classifications are used to distinguish between its different subtypes. The distinctions between the major types are usually drawn based on the linguistic formulations used to express them. Propositional knowledge is ''propositional'' in the sense that it involves a relation to a proposition. Since propositions are often expressed through that-clauses, it is also referred to as ''knowledge-that'', as in "Akari knows that
Canberra Canberra ( ) is the capital city of Australia. Founded following the Federation of Australia, federation of the colonies of Australia as the seat of government for the new nation, it is Australia's largest inland city and the List of citi ...
is the capital of
Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...
". In this case, Akari stands in the relation of knowing to the proposition "Canberra is the capital of Australia". Closely related types of knowledge are ''know-wh'', for example, ''knowing where'' the
Taj Mahal The Taj Mahal (; ) is an Islamic architecture, Islamic ivory-white marble mausoleum on the right bank of the river Yamuna in the Indian city of Agra. It was commissioned in 1631 by the Mughal Empire, Mughal emperor Shah Jahan () to house ...
is or ''knowing who'' killed J. F. Kennedy. These expressions are normally understood as types of propositional knowledge since they usually can be paraphrased using a that-clause. Propositional knowledge is either occurrent and dispositional. This mirrors the distinction between occurrent and dispositional beliefs: to know occurrently means to entertain the corresponding representation currently, to be aware of it. "Dispositional knowledge" refers to the mere ability to do so without its execution. In this regard, a person fully immersed in a go-kart race has dispositional but not occurrent knowledge of where their home is. The reason is that they are currently occupied with something else but could easily provide this information if they stopped and focused on it.


Non-propositional knowledge

For non-propositional knowledge, no essential relation to a proposition is involved. The two most well-known forms are knowledge-how (know-how or
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 knowledge (also kno ...
) and knowledge by acquaintance. The term "know-how" refers to some form of practical ability or skill. It can be defined as having the corresponding competence. Examples include knowing how to ride a bicycle or knowing how to play the guitar. Some of the abilities responsible for know-how may also involve certain forms of knowledge-that, as in knowing how to prove a
mathematical Mathematics is an area of knowledge that includes the topics of numbers, formulas and related structures, shapes and the spaces in which they are contained, and quantities and their changes. These topics are represented in modern mathematics ...
theorem. But this is not generally the case. It is usually argued that mainly humans and maybe other higher animals possess propositional knowledge since it requires an advanced form of mind. Practical knowledge, on the other hand, is more common in the animal kingdom. In this regard, an
ant Ants are eusocial insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from vespoid wasp ancestors in the Cretaceous period. More than 13,800 of an estimated total of 22 ...
knows how to walk even though it presumably lacks a mind sufficiently developed enough to stand in a relation to the corresponding proposition by representing it. Knowledge by acquaintance refers to familiarity with an individual that results from direct experiential contact with this individual. It often, but not exclusively, concerns a relation to a person. On the linguistic level, it does not require a that-clause and can be expressed using a
direct object In linguistics, an object is any of several types of Argument (linguistics), arguments. In subject-prominent, nominative-accusative languages such as English language, English, a transitive verb typically distinguishes between its Subject (lingu ...
. So when someone claims that they know Wladimir Klitschko personally, they are expressing that they had a certain kind of contact with him and not that they know a certain fact about him. This is usually understood to mean that it constitutes a relation to a concrete individual and not to a proposition. Knowledge by acquaintance plays a central role in
Bertrand Russell Bertrand Arthur William Russell, 3rd Earl Russell, (18 May 1872 – 2 February 1970) was a British mathematician, philosopher, logician, and public intellectual. He had a considerable influence on mathematics, logic, set theory, linguistics, ar ...
's epistemology. He contrasts it with knowledge by description, which is a form of propositional knowledge not based on direct perceptual experience. So by watching a documentary about
Wladimir Klitschko Wladimir Klitschko; an equivalent English spelling is Vladimir Klichko . His full name in uk, label=Ukrainian language, Ukrainian is, Володимир Володимирович Кличко, Volodymyr Volodymyrovych Klychko, . ( uk, Вол ...
, the viewer may acquire various forms of knowledge by description about him, for example, about his nationality or his career in boxing, without acquiring knowledge by acquaintance of him. However, there is some controversy about whether it is possible to acquire knowledge by acquaintance in its pure non-propositional form. In this regard, some theorists have suggested that it might be better to understand it as one type of propositional knowledge that is only expressed in a grammatically different way.


Other distinctions


A priori and a posteriori

The distinction between a priori and a posteriori knowledge came to prominence in
Immanuel Kant Immanuel Kant (, , ; 22 April 1724 – 12 February 1804) was a German Philosophy, philosopher and one of the central Age of Enlightenment, Enlightenment thinkers. Born in Königsberg, Kant's comprehensive and systematic works in epistemolo ...
's philosophy and is often discussed in the academic literature. To which category a knowledge attitude belongs depends on the role of experience in its formation and justification. To know something a posteriori means to know it on the basis of experience. For example, to know that it is currently raining or that the baby is crying belongs to a posteriori knowledge since it is based on some form of experience, like visual or auditory experience. A priori knowledge, on the other hand, is possible without any experience to justify or support the known proposition. Mathematical knowledge, for example, that 2 + 2 = 4, is a paradigmatic case of a priori knowledge since no empirical investigation is necessary to confirm this fact. The distinction between a posteriori and a priori knowledge is usually equated with the distinction between empirical and non-empirical knowledge. This distinction pertains primarily to knowledge but it can also be applied to propositions or arguments. For example, an a priori proposition is a proposition that can be known independently of experience. The prime example of the relevant experience in question is
sensory experience The theory of sense data is a view in the philosophy of perception, popularly held in the early 20th century by philosophers such as Bertrand Russell, C. D. Broad, H. H. Price, A. J. Ayer, and G. E. Moore. Sense data are taken to be mind-depende ...
. However, some non-sensory experiences, like memory and introspection, are often included as well. But certain conscious phenomena are excluded in this context. For example, the conscious phenomenon of a rational insight into the solution of a mathematical problem does not make the resulting knowledge a posteriori. It is sometimes pointed out that, in a trivial sense, some form of experience is required even for a priori knowledge: the experience needed to learn the language in which the claim is expressed. For a priori knowledge, this is the only form of experience required. For this reason, knowing that "all bachelors are unmarried" is considered a form of a priori knowledge since, given an understanding of the terms "bachelor" and "unmarried", no further experience is necessary to know that it is true. One difficulty for a priori knowledge is to explain how it is possible. It is usually seen as unproblematic that one can come to know things through experience but it is not clear how knowledge is possible without experience. One of the earliest solutions to this problem is due to Plato, who argues that, in the context of
geometry Geometry (; ) is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space such as the distance, shape, size, and relative position of figures. A mathematician who works in the field of geometry is ca ...
, the soul already possesses the knowledge and just needs to recollect or remember it to access it again. A similar explanation is given by
René Descartes René Descartes ( or ; ; Latinisation of names, Latinized: Renatus Cartesius; 31 March 1596 – 11 February 1650) was a French people, French philosopher, scientist, and mathematician, widely considered a seminal figure in the emergence of m ...
, who holds that a priori knowledge exists as innate knowledge present in the
mind The mind is the set of faculties responsible for all mental Phenomenon, phenomena. Often the term is also identified with the phenomena themselves. These faculties include thought, imagination, memory, Will (philosophy), will, and Sensation (psy ...
of each human. A different approach is to posit a special mental faculty responsible for this type of knowledge, often referred to as ''rational insight'' or ''rational intuition''. The distinction between a priori and a posteriori knowledge is closely related to two other distinctions: the distinction between analytic and synthetic propositions and the distinction between necessary and contingent propositions. Traditionally, it was often assumed that these distinctions coincide. On this view, a priori knowledge concerns propositions that are analytic and necessary while a posteriori knowledge is about propositions that are synthetic and contingent. However, this position is rejected by many contemporary philosophers. One reason is that these distinctions belong to different fields. The a priori–a posteriori distinction belongs to
epistemology Epistemology (; ), or the theory of knowledge, is the branch of philosophy concerned with knowledge. Epistemology is considered a major subfield of philosophy, along with other major subfields such as ethics, logic, and metaphysics. Epis ...
and is about how one knows things. The analytic–synthetic distinction pertains to
semantics Semantics (from grc, wikt:σημαντικός, σημαντικός ''sēmantikós'', "significant") is the study of reference, Meaning (philosophy), meaning, or truth. The term can be used to refer to subfields of several distinct discipline ...
and concerns how the meanings of terms make a proposition true. The necessary–contingent distinction is
metaphysical Metaphysics is the branch of philosophy that studies the fundamental nature of reality, the first principles of being, identity and change, space and time, causality, necessity, and possibility. It includes questions about the nature of conscio ...
and asks, for example, whether a proposition is true in all
possible world A possible world is a complete and consistent way the world is or could have been. Possible worlds are widely used as a formal device in logic, philosophy, and linguistics in order to provide a semantics for intensional logic, intensional and mod ...
s or just in some of them. Various discussions in the academic literature concern the question of how these distinctions overlap or fail to overlap, for example, on cases of synthetic a priori truths or of contingent a priori truths.


Self-knowledge

In philosophy, "self-knowledge" usually refers to a person's knowledge of their own sensations,
thought In their most common sense, the terms thought and thinking refer to conscious cognitive Cognition refers to "the mental action or process of acquiring knowledge and understanding through thought, experience, and the senses". It encompasse ...
s, beliefs, and other mental states. Many philosophers hold that it is a special type of knowledge since it is more direct than knowledge of the external world, which is mediated through the senses. Traditionally, it was often claimed that self-knowledge is indubitable, for example, that when someone is in pain, they cannot be wrong about this fact. However, various contemporary theorists reject this position. A closely related issue is to explain how self-knowledge works. Some understand it as a form of knowledge by acquaintance while others claim that there is an inner sense that works in analogy to how the external five senses work. According to a different perspective, self-knowledge is indirect in the sense that a person has to interpret their internal and external behavior in order to learn about their mental states, similar to how one can learn about the mental states of other people by interpreting their external behavior. In a slightly different sense, the term ''self-knowledge'' can also refer to the knowledge of the
self The self is an individual as the object of that individual’s own reflective consciousness. Since the ''self'' is a reference by a subject to the same subject, this reference is necessarily Subjective character of experience, subjective. The sen ...
as a persisting entity that has certain personality traits,
preference In psychology Psychology is the science, scientific study of mind and behavior. Psychology includes the study of consciousness, conscious and Unconscious mind, unconscious phenomena, including feelings and thoughts. It is an academic disc ...
s, physical attributes, relationships, goals, and social identities. This meaning is of particular interest to
psychology Psychology is the science, scientific study of mind and behavior. Psychology includes the study of consciousness, conscious and Unconscious mind, unconscious phenomena, including feelings and thoughts. It is an academic discipline of immens ...
and refers to a person's awareness of their own characteristics. Self-knowledge is closely related to
self-concept In the psychology of self, one's self-concept (also called self-construction, self-identity, self-perspective or self-structure) is a collection of beliefs about oneself. Generally, self-concept embodies the answer to the question ''"Who am I? ...
, the difference being that the self-concept also includes unrealistic aspects of how a person sees themselves. In this regard, self-knowledge is often measured by comparing a person's self-assessment of their character traits with how other people assess this person's traits.


Situated knowledge

Situated knowledge is knowledge specific to a particular situation. It is closely related to practical or tacit knowledge, which is learned and applied in specific circumstances. This especially concerns certain forms of acquiring knowledge, such as
trial and error Trial and error is a fundamental method of problem-solving characterized by repeated, varied attempts which are continued until success, or until the practicer stops trying. According to W.H. Thorpe, the term was neologism, devised by C. Lloyd ...
or learning from experience. In this regard, situated knowledge usually lacks a more explicit structure and is not articulated in terms of universal ideas. The term is often used in
feminism Feminism is a range of socio-political movements and ideologies that aim to define and establish the political, economic, personal, and social equality of the sexes. Feminism incorporates the position that society prioritizes the male po ...
and
postmodernism Postmodernism is an intellectual stance or mode of discourseNuyen, A.T., 1992. The Role of Rhetorical Devices in Postmodernist Discourse. Philosophy & Rhetoric, pp.183–194. characterized by skepticism Skepticism, also spelled scepticism ...
to point out that many forms of knowledge are not absolute but depend on the concrete historical, cultural, and linguistic context. Understood in this way, it is frequently used to argue against absolute or universal knowledge claims stated in the scientific discourse.
Donna Haraway Donna J. Haraway is an American Professor Emeritus, Emerita in the History of Consciousness Department and Feminist studies, Feminist Studies Department at the University of California, Santa Cruz, and a prominent scholar in the field of science ...
is a prominent defender of this position. One of her arguments is based on the idea that perception is embodied and is not a universal "gaze from nowhere". The
American Psychological Association The American Psychological Association (APA) is the largest scientific and professional organization of psychologists in the United States, with over 133,000 members, including scientists, educators, clinicians, consultants, and students. It has ...
notes that some interpreters associate with this position a form of epistemological relativism because of how knowledge depends on the local conditions of the culture in which it arises. Haraway herself criticised relativism:


Higher and lower knowledge

Many forms of eastern spirituality and religion distinguish between ''higher'' and ''lower knowledge''. They are also referred to as para vidya and apara vidya in
Hinduism Hinduism () is an Indian religions, Indian religion or ''dharma'', a religious and universal order or way of life by which followers abide. As a religion, it is the Major religious groups, world's third-largest, with over 1.2–1.35 billion ...
or the
two truths doctrine The Buddhist doctrine of the two truths (Sanskrit Sanskrit (; attributively , ; nominalization, nominally , , ) is a classical language belonging to the Indo-Aryan languages, Indo-Aryan branch of the Indo-European languages. It arose in So ...
in
Buddhism Buddhism ( , ), also known as Buddha Dharma and Dharmavinaya (), is an Indian religions, Indian religion or Indian philosophy#Buddhist philosophy, philosophical tradition based on Pre-sectarian Buddhism, teachings attributed to the Buddha. ...
. Lower knowledge is based on the senses and the intellect. In this regard, all forms of empirical and objective knowledge belong to this category. Most of the knowledge needed in one's everyday functioning is lower knowledge. It is about mundane or conventional things that are in tune with common sense, like that mice are smaller than elephants. It is relevant to many practical issues, like how to repair a car or how to persuade a customer. Scientific knowledge, for example, that the chemical composition of water is H2O, is often seen as one of the most advanced forms of lower knowledge. Higher knowledge, on the other hand, is understood as knowledge of
God In monotheistic thought, God is usually viewed as the supreme being, creator, and principal object of faith. Swinburne, R.G. "God" in Honderich, Ted. (ed)''The Oxford Companion to Philosophy'', Oxford University Press, 1995. God is typicall ...
,
the absolute Georg Wilhelm Friedrich Hegel (; ; 27 August 1770 – 14 November 1831) was a German philosopher A philosopher is a person who practices or investigates philosophy Philosophy (from , ) is the systematized study of general and fun ...
, the true self, or the ultimate reality. It belongs neither to the external world of physical objects nor to the internal world of the experience of emotions and concepts. Many spiritual teachings emphasize the increased importance, or sometimes even exclusive importance, of higher knowledge in comparison to lower knowledge. This is usually based on the idea that achieving higher knowledge is one of the central steps on the spiritual path. In this regard, higher knowledge is seen as what frees the individual from ignorance, helps them realize God, or liberates them from the cycle of rebirth. This is often combined with the view that lower knowledge is in some way based on a delusion: it belongs to the realm of mere appearances or
Maya Maya may refer to: Civilizations * Maya peoples, of southern Mexico and northern Central America ** Maya civilization, the historical civilization of the Maya peoples ** Maya language (disambiguation), Maya language, the languages of the Maya peop ...
, while higher knowledge manages to view the reality underlying these appearances. In the Buddhist tradition, the attainment of higher knowledge or ultimate truth is often associated with seeing the world from the perspective of sunyata, i.e. as a form of
emptiness Emptiness as a human condition is a sense of generalized boredom, social alienation and apathy. Feelings of emptiness often accompany dysthymia, depression (mood), depression, loneliness, anhedonia, wiktionary:despair, despair, or other mental/em ...
lacking inherent existence or intrinsic nature.


Sources of knowledge

Sources of knowledge are "rational capacities for knowledge" or ways how people come to know things. Various sources of knowledge are discussed in the academic literature, often in terms of the mental faculties responsible. They include perception, introspection, memory, inference, and testimony. However, not everyone agrees that all of them actually lead to knowledge. Usually,
perception Perception () is the organization, identification, and interpretation of sensory information in order to represent and understand the presented information or environment. All perception involves signals that go through the nervous syste ...
or observation, i.e. using one of the
senses A sense is a biological system A biological system is a complex biological network, network which connects several biologically relevant entities. Biological organization spans several scales and are determined based different structures dep ...
, is identified as the most important source of empirical knowledge. So knowing that the baby is sleeping constitutes observational knowledge if it was caused by a perception of the snoring baby. But this would not be the case if one learned about this fact through a telephone conversation with one's spouse. Direct realists explain observational knowledge by holding that perception constitutes a direct contact with the perceived object. Indirect realists, on the other hand, contend that this contact happens indirectly: we can only directly perceive
sense data The theory of sense data is a view in the philosophy of perception The philosophy of perception is concerned with the nature of Perception, perceptual experience and the status of sense data, perceptual data, in particular how they relate to b ...
, which are then interpreted as representing external objects. This distinction is important since it affects whether the knowledge of external objects is direct or indirect and may thus have an impact on how certain the knowledge is.
Introspection Introspection is the examination of one's own conscious thoughts and feelings. In psychology Psychology is the science, scientific study of mind and behavior. Psychology includes the study of consciousness, conscious and Unconscious m ...
is often seen in analogy to perception as a source of knowledge, not of external physical objects, but of internal
mental states A mental state, or a mental property, is a state of mind of a person. Mental states comprise a diverse class, including perception, pain experience, belief, desire, intention, emotion, and memory. There is controversy concerning the exact definitio ...
. Traditionally, various theorists have ascribed a special epistemic status to introspection by claiming that it is infallible or that there is no introspective difference between appearance and reality. However, this claim has been contested in the contemporary discourse. Critics argue that it may be possible, for example, to mistake an unpleasant itch for a pain or to confuse the experience of a slight ellipse for the experience of a circle. Perceptual and introspective knowledge often act as a form of fundamental or basic knowledge. According to some
empiricists In philosophy Philosophy (from , ) is the systematized study of general and fundamental questions, such as those about existence, reason, knowledge, values, mind, and language. Such questions are often posed as problems to be stud ...
, perceptual knowledge is the only source of basic knowledge and provides the foundation for all other knowledge. Memory is usually identified as another source of knowledge. It differs from perception and introspection in that it is not as independent or fundamental as they are since it depends on other previous experiences. The faculty of memory retains knowledge acquired in the past and makes it accessible in the present, as when remembering a past event or a friend's phone number. It is generally considered a reliable source of knowledge, but it may deceive us at times nonetheless, either because the original experience was unreliable or because the memory degraded and does not accurately represent the original experience anymore. Knowledge based on perception, introspection, or memory may also give rise to ''inferential knowledge'', which comes about when reasoning is applied to draw inferences from another known fact. In this regard, the perceptual knowledge of a Czech stamp on a postcard may give rise to the inferential knowledge that one's friend is visiting the Czech Republic. According to
rationalists In philosophy Philosophy (from , ) is the systematized study of general and fundamental questions, such as those about existence, reason, knowledge, values, mind, and language. Such questions are often posed as problems to be studied ...
, some forms of knowledge are completely independent of observation and introspection. They are needed to explain how certain a priori beliefs, like the mathematical belief that 2 + 2 = 4, constitute knowledge. Some theorists hold that the faculty of ''pure reason'' or ''rational intuition'' is responsible in these cases since there seem to be no sensory perceptions that could justify such general and abstract knowledge. However, difficulties in providing a clear account of pure reason or rational intuition have led various empirically minded epistemologists to doubt that they constitute independent sources of knowledge. A closely related approach is to hold that this type of knowledge is ''innate''. According to Plato's theory of recollection, for example, it is accessed through a special form of remembering.
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 ...
is often included as an additional source of knowledge. Unlike the other sources, it is not tied to one specific cognitive faculty. Instead, it is based on the idea that one person can come to know a fact because another person talks about this fact. Testimony can happen in numerous ways, like regular speech, a letter, the newspaper, or an online blog. The problem of testimony consists in clarifying under what circumstances and why it constitutes a source of knowledge. A popular response is that it depends on the reliability of the person pronouncing the testimony: only testimony from reliable sources can lead to knowledge.


Structure of knowledge

The expression "structure of knowledge" refers to the way in which the mental states of a person need to be related to each other for knowledge to arise. Most theorists hold that, among other things, an agent has to have good reasons for holding a belief if this belief is to amount to knowledge. So when challenged, the agent may justify their belief by referring to their reason for holding it. In many cases, this reason is itself a belief that may as well be challenged. So when the agent believes that Ford cars are cheaper than BMWs because they believe to have heard this from a reliable source, they may be challenged to justify why they believe that their source is reliable. If it turns out that their reasons are not well supported, this also affects the epistemic status of the original belief. However, whatever support they present may also be challenged. This threatens to lead to an
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 beca ...
since the epistemic status at each step depends on the epistemic status of the previous step. Theories of the structure of knowledge offer responses for how to solve this problem. The three most common theories are
foundationalism Foundationalism concerns epistemology, philosophical theories of knowledge resting upon non-inferential knowledge, justified belief, or some secure foundation of certainty such as a conclusion inferred from a basis of sound premises.Simon Blackbu ...
,
coherentism In philosophy, philosophical epistemology, there are two types of coherentism: the coherence theory of truth; and the coherence theory of justification (also known as epistemic coherentism). Coherent truth is divided between an anthropological ap ...
, and infinitism. Foundationalists and coherentists deny the existence of this infinite regress, in contrast to infinitists. According to foundationalists, some ''basic reasons'' have their epistemic status independent of other reasons and thereby constitute the endpoint of the regress. Against this view, it has been argued that the concept of "basic reason" is contradictory: there should be a reason for why some reasons are basic and others are non-basic, in which case the basic reasons would depend on another reason after all and would therefore not be basic. An additional problem consists in finding plausible candidates for basic reasons. Coherentists and infinitists avoid these problems by denying the distinction between basic and non-basic reasons. Coherentists argue that there is only a finite number of reasons, which mutually support each other and thereby ensure each other's epistemic status. Their critics contend that this constitutes the fallacy of
circular reasoning Circular may refer to: * The shape of a circle * Circular (album), ''Circular'' (album), a 2006 album by Spanish singer Vega * Circular letter (disambiguation) ** Flyer (pamphlet), a form of advertisement * Circular reasoning, a type of logical fa ...
. For example, if belief ''b1'' supports belief ''b2'' and belief ''b2'' supports belief ''b1'', the agent has a reason for accepting one belief if they already have the other. However, their mutual support alone is not a good reason for newly accepting both beliefs at once. A closely related issue is that there can be various distinct sets of coherent beliefs and coherentists face the problem of explaining why we should accept one coherent set rather than another. For infinitists, in contrast to foundationalists and coherentists, there is an infinite number of reasons. This position faces the problem of explaining how human knowledge is possible at all since it seems that the human mind is limited and cannot possess an infinite number of reasons. In their traditional forms, foundationalists, coherentists and infinitists all face the
Gettier problem The Gettier problem, in the field of epistemology, is a landmark philosophy, philosophical problem concerning the understanding of descriptive knowledge. Attributed to American philosopher Edmund Gettier, Gettier-type counterexamples (called "Gett ...
, i.e. that having a reason or justification for a true belief is not sufficient for knowledge in cases where cognitive luck is responsible for the success.


Value of knowledge

The value of knowledge is an important topic in epistemology. Its main question is whether or why knowledge is more valuable than mere true belief. There is wide agreement that knowledge is good in some sense. For example, knowledge can help a student pass the exam or ensure that a doctor prescribes the right medicine. However, the thesis that knowledge is better than true belief is more controversial. An early discussion of this problem is found in Plato's
Meno ''Meno'' (; grc-gre, wikt:Μένων, Μένων, ''Ménōn'') is a Socratic dialogue by Plato. Meno (general), Meno begins the dialogue by asking Socrates whether virtue is taught, acquired by practice, or comes by nature. In order to determ ...
in relation to the claim that both knowledge and true belief can successfully guide
action Action may refer to: * Action (narrative) In literature, action is the physical movement of the Character (arts), characters. Action as a literary mode "Action is the Mode (literature), mode hat A hat is a head covering which is worn for ...
and, therefore, have apparently the same value. For example, it seems that mere true belief is as effective as knowledge when trying to find the way to
Larissa Larissa (; el, Λάρισα, , ) is the capital and largest city of the Thessaly modern regions of Greece, region in Greece. It is the fifth-most populous city in Greece with a population of 144,651 according to the 2011 census. It is also capit ...
. According to Plato, knowledge is better because it is more stable. A different approach is to hold that knowledge gets its additional value from justification. However, if the value in question is understood primarily as an
instrumental value In moral philosophy Ethics or moral philosophy is a branch of philosophy that "involves systematizing, defending, and recommending concepts of morality, right and wrong action (philosophy), behavior".''Internet Encyclopedia of Philosophy'' T ...
, it is not clear in what sense knowledge is better than mere true belief since they are usually equally useful. The problem of the value of knowledge is often discussed in relation to
reliabilism Reliabilism, a category of theories in the philosophy, philosophical discipline of epistemology, has been advanced as a theory both of Theory of justification, justification and of knowledge. Process reliabilism has been used as an argument against ...
and
virtue epistemology Virtue epistemology is a contemporary philosophy, philosophical approach to epistemology that stresses the importance of intellectual and specifically epistemic virtues. A distinguishing factor of virtue theories is that they use for the evaluation ...
. Reliabilism can be defined as the thesis that knowledge is reliably-formed true belief. On this view, it seems difficult to explain how a reliable belief-forming process adds additional value. According to an analogy by Linda Zagzebski, a cup of coffee made by a reliable coffee machine has the same value as an equally good cup of coffee made by an unreliable coffee machine. This difficulty in solving the value problem is sometimes used as an argument against reliabilism. Virtue epistemologists have a different approach to the value problem. They see knowledge as the manifestation of cognitive virtues and can thus argue that knowledge has additional value due to its association with virtue. However, not everyone agrees that knowledge actually has additional value over true belief. A similar view is defended by Jonathan Kvanvig, who argues that the main epistemic value resides not in knowledge but in
understanding Understanding is a psychological process related to an abstract or physical object, such as a person, situation, or message whereby one is able to use concepts to model that object. Understanding is a relation between the knower and an obje ...
, which implies grasping how one's beliefs cohere with each other.


Philosophical skepticism

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 ...
in its strongest form, also referred to as ''global skepticism'', is the thesis that we lack any form of knowledge or that knowledge is impossible. This position is quite radical and very few philosophers have explicitly defended it. However, it has been influential nonetheless, usually in a negative sense: many researchers see it as a serious challenge to any epistemological theory and often try to show how their preferred theory overcomes it. For example, it is commonly accepted that perceptual experience constitutes a source of knowledge. However, according to the dream argument, this is not the case since dreaming provides unreliable information and since the agent could be dreaming in that moment. In this case, they would be unable to distinguish actual perceptual experience from the dreaming experience. Since they may be dreaming at any time without being aware of this, it is then argued that there is no perceptual knowledge. A similar often cited
thought experiment A thought experiment is a hypothetical situation in which a hypothesis, theory, or principle is laid out for the purpose of thinking through its consequences. History The ancient Greek ''deiknymi'' (), or thought experiment, "was the most anci ...
assumes that the agent is actually a
brain in a vat In philosophy Philosophy (from , ) is the systematized study of general and fundamental questions, such as those about existence, reason, knowledge, values, mind, and language. Such questions are often posed as problems to be studie ...
that is just fed electrical stimuli. Such a brain would have the false impression of having a body and interacting with the external world. The basic thrust of the argument is the same: since the agent is unable to tell the difference, they do not know that they have a body responsible for reliable perceptions. One issue revealed through these thought experiments is the problem of
underdetermination In the philosophy of science, underdetermination or the underdetermination of theory by data (sometimes abbreviated UTD) is the idea that evidence available to us at a given time may be insufficient to determine what beliefs we should hold in re ...
: that the evidence available is not sufficient to make a rational decision between competing theories. And if two contrary hypotheses explain the appearances equally well then the agent is not justified in believing one of those hypotheses rather than the other. Based on this premise, the general skeptic just has to argue that this is true for all our knowledge, that there is always an alternative and very different explanation. Another skeptic argument is based on the idea that human cognition is fallible and therefore lacks absolute certainty. More specific arguments target particular theories of knowledge, such as foundationalism or coherentism, and try to show that their concept of knowledge is deeply flawed. An important argument against global skepticism is that it seems to contradict itself: the claim that there is no knowledge appears to constitute a knowledge-claim itself. Other responses come from common sense philosophy and reject global skepticism based on the fact that it contradicts common sense. It is then argued against skepticism by seeing common sense as more reliable than the abstract reasoning cited in favor of skepticism. Certain less radical forms of skepticism deny that knowledge exists within a specific area or discipline, sometimes referred to as ''local'' or ''selective skepticism''. It is often motivated by the idea that certain phenomena do not accurately represent their subject matter. They may thus lead to false impressions concerning its nature. External world skeptics hold that we can only know about our own sensory impressions and experiences but not about the external world. This is based on the idea that beliefs about the external world are mediated through the senses. The senses are faulty at times and may thus show things that are not really there. This problem is avoided on the level of sensory impressions, which are given to the experiencer directly without an intermediary. In this sense, the person may be wrong about seeing a red Ferrari in the street (it might have been a Maserati or a mere light reflection) but they cannot be wrong about having a sensory impression of seeing a patch of red color. The inverse path is taken by some materialists, who accept the existence of the external physical world but deny the existence of the internal realm of mind and consciousness based on the difficulty of explaining how the two realms can exist together. Other forms of local skepticism accept scientific knowledge but deny the possibility of moral knowledge, for example, because there is no reliable way to empirically measure whether a moral claim is true or false. The issue of the definition and standards of knowledge is central to the question of whether skepticism in its different forms is true. If very high standards are used, for example, that knowledge implies infallibility, then skepticism becomes more plausible. In this case, the skeptic only has to show that no belief is absolutely certain; that while the actual belief is true, it could have been false. However, the more these standards are weakened to how the term is used in everyday language, the less plausible skepticism becomes.


In various disciplines


Formal epistemology

Formal epistemology Formal epistemology uses formal methods from decision theory, 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, c ...
studies knowledge using formal tools, such as mathematics and logic. An important issue in this field concerns the epistemic principles of knowledge. They are rules governing how knowledge and related states behave and in what relations they stand to each other. The transparency principle, also referred to as the ''luminosity of knowledge'', is an often discussed principle. It states that knowing something implies the second-order knowledge that one knows it. So if Heike knows that today is Monday, then she also knows that she knows that today is Monday. According to the ''conjunction principle'', having two justified beliefs in two separate propositions implies that the agent is also justified in believing in the conjunction of these two propositions. The ''closure principle'' states that if the agent has a justified belief in one proposition and this proposition entails another proposition, then the agent is also justified in believing this other proposition. The ''evidence transfer principle'' applies this idea to evidence: if, in the case above, a certain piece of evidence justifies the first belief then it also justifies the second belief.


Science

The development of the
scientific method The scientific method is an Empirical evidence, empirical method for acquiring knowledge that has characterized the development of science since at least the 17th century (with notable practitioners in previous centuries; see the article hist ...
has made a significant contribution to how knowledge of the physical world and its phenomena is acquired. To be termed scientific, a method of
inquiry An inquiry (also spelled as enquiry in British English British English (BrE, en-GB, or BE) is, according to Oxford Dictionaries, " English as used in Great Britain, as distinct from that used elsewhere". More narrowly, it can refer s ...
must be based on gathering
observable In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its motion and behavior through Spacetime, space and time, and the related entities of energy and force. "Physical scien ...
and
measurable In mathematics, the concept of a measure is a generalization and formalization of Geometry#Length, area, and volume, geometrical measures (length, area, volume) and other common notions, such as mass and probability of events. These seemingly ...
evidence subject to specific principles of reasoning and experimentation. The scientific method consists of the collection of
data In the pursuit of knowledge, data (; ) is a collection of discrete values that convey information, describing quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interp ...
through
observation Observation is the active acquisition of information from a primary source. In living beings, observation employs the senses. In science, observation can also involve the perception and recording of data (information), data via the use of scienti ...
and
experiment An experiment is a procedure carried out to support or refute a hypothesis, or determine the efficacy or likelihood of something previously untried. Experiments provide insight into cause-and-effect by demonstrating what outcome occurs wh ...
ation, and the formulation and testing of
hypotheses A hypothesis (plural hypotheses) is a proposed explanation for a phenomenon A phenomenon (plural, : phenomena) is an observable event. The term came into its modern Philosophy, philosophical usage through Immanuel Kant, who contrasted i ...
. Science and the nature of scientific knowledge have also become the subject of
philosophy Philosophy (from , ) is the systematized study of general and fundamental questions, such as those about existence, reason, knowledge, values, mind, and language. Such questions are often posed as problems to be studied or resolved. Some ...
. As science itself has developed, scientific knowledge now includes a broader usage in the soft sciences such as the
social science Social science is one of the branches of science, devoted to the study of society, societies and the Social relation, relationships among individuals within those societies. The term was formerly used to refer to the field of sociology, the o ...
s.
Sir 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 Lord Chancellor of King ...
was critical of the historical development of the scientific method; his works established and popularized an inductive methodology for scientific inquiry. His aphorism, "
knowledge is power The phrase "" (or "" or also "") is a Latin aphorism meaning "knowledge is power", commonly attributed to Sir Francis Bacon. The expression "" ('knowledge itself is power') occurs in Bacon's ''Meditationes Sacrae'' (1597). The exact phrase "" ( ...
", is found in the Meditations Sacrae (1597).


Religion

Knowledge plays a central role in many
religion Religion is usually defined as a social- cultural system of designated behaviors and practices, morals, beliefs, worldviews, texts, sanctified places, prophecies, ethics, or religious organization, organizations, that generally relates hu ...
s. Knowledge claims about the
existence of God The existence of God (or more generally, the existence of deities) is a subject of debate in theology, philosophy of religion and popular culture. A wide variety of arguments for and against the existence of God or deities can be categorized ...
or religious doctrines about how each one should live their lives are found in almost every culture. However, such knowledge claims are often controversial and are commonly rejected by religious skeptics and
atheists Atheism, in the broadest sense, is an absence of belief in the existence of Deity, deities. Less broadly, atheism is a rejection of the belief that any deities exist. In an even narrower sense, atheism is specifically the position that ther ...
. The epistemology of religion is the field of inquiry that investigates whether belief in God and in other religious doctrines is
rational Rationality is the Quality (philosophy), quality of being guided by or based on reasons. In this regard, a person Action (philosophy), acts rationally if they have a good reason for what they do or a belief is rational if it is based on strong e ...
and amounts to knowledge. It is different from other forms of epistemology because of its unique subject matter. One important view in this field is evidentialism. It states that belief in religious doctrines is justified if it is supported by sufficient evidence. Suggested examples of evidence for religious doctrines include
religious experience A religious experience (sometimes known as a spirituality, spiritual experience, sacred experience, or mysticism, mystical experience) is a subjectivity, subjective experience which is interpreted within a religious framework. The concept origin ...
s such as direct contact with the divine or inner testimony as when hearing God's voice. However, evidentialists often reject that belief in religious doctrines amount to knowledge based on the claim that we lack sufficient evidence. A famous saying in this regard is due to Bertrand Russell. When asked how he would justify his lack of belief in God when facing His judgment after death, he replied "Not enough evidence, God! Not enough evidence." However, religious teachings about the existence and nature of God are not always understood as knowledge claims by their defenders and some explicitly state that the proper attitude towards such doctrines is not knowledge but
faith Faith, derived from Latin ''fides'' and Old French ''feid'', is confidence or trust in a person, thing, or In the context of religion, one can define faith as "belief in God or in the doctrines or teachings of religion". Religious people often ...
. This is often combined with the assumption that these doctrines are true but cannot be fully understood by reason or verified through rational inquiry. For this reason, it is claimed that one should accept them even though they do not amount to knowledge. Such a view is reflected in a famous saying by Immanuel Kant where he claims that he "had to deny knowledge in order to make room for faith." Distinct religions often differ from each other concerning the doctrines they proclaim as well as their understanding of the role of knowledge in religious practice. Knowledge plays a central role in
Abrahamic religions The Abrahamic religions are a group of religions centered around worship of the God in Abrahamic religions, God of Abraham. Abraham, a Hebrews , Hebrew patriarch, is extensively mentioned throughout Abrahamic religious scriptures such as the B ...
. In
Jewish Jews ( he, יְהוּדִים, , ) or Jewish people are an ethnoreligious group and nation A nation is a community of people formed on the basis of a combination of shared features such as language, history, ethnicity, culture and/or ...
tradition, knowledge (
Hebrew Hebrew (; ; ) is a Northwest Semitic languages, Northwest Semitic language of the Afroasiatic languages, Afroasiatic language family. Historically, it is one of the spoken languages of the Israelites and their longest-surviving descendants, ...
: דעת ''da'ath'') is considered one of the most valuable traits a person can acquire. Observant Jews recite three times a day in the
Amidah The ''Amidah Amuhduh'' ( he, תפילת העמידה, ''Tefilat HaAmidah'', 'The Standing Prayer'), also called the ''Shemoneh Esreh'' ( 'eighteen'), is the central prayer of the Jewish liturgy. Observant Jews recite the ''Amidah'' at each ...
"You favor people with knowledge and teach mortals understanding. Favor us with your knowledge, understanding, and wisdom. Blessed are you, Adonai, who favors people with knowledge." The
Tanakh The Hebrew Bible or Tanakh (;"Tanach"
'' Old Testament The Old Testament (often abbreviated OT) is the first division of the Christian biblical canon, which is based primarily upon the 24 books of the Hebrew Bible The Hebrew Bible or Tanakh (;
's
tree of the knowledge of good and evil In Judaism Judaism ( he, ''Yahăḏūṯ'') is an Abrahamic religions, Abrahamic, monotheism, monotheistic, and ethnic religion comprising the collective religious, cultural, and legal tradition and civilization of the Jewish people. It ...
contained the knowledge that separated Man from God: "And the LORD God said, Behold, the man is become as one of us, to know good and evil..." () In many expressions of
Christianity Christianity is an Abrahamic religions, Abrahamic Monotheism, monotheistic religion based on the Life of Jesus in the New Testament, life and Teachings of Jesus, teachings of Jesus, Jesus of Nazareth. It is the Major religious groups, world's ...
, such as
Catholicism The Catholic Church, also known as the Roman Catholic Church, is the List of Christian denominations by number of members, largest Christian church, with 1.3 billion baptized Catholics Catholic Church by country, worldwide . It is am ...
and
Anglicanism Anglicanism is a Western Christianity, Western Christian tradition that has developed from the practices, liturgy, and identity of the Church of England following the English Reformation, in the context of the Protestant Reformation in Euro ...
, knowledge is one of the
seven gifts of the Holy Spirit The seven gifts of the Holy Spirit are an enumeration of seven spiritual gifts first found in the book of Isaiah, and much commented upon by patristic authors. They are: wisdom, understanding, counsel, fortitude, knowledge, piety, and fear of ...
. As
Pope Francis Pope Francis ( la, Franciscus; it, Francesco; es, link=, Francisco; born Jorge Mario Bergoglio, 17 December 1936) is the head of the Catholic Church. He has been the bishop of Rome and sovereign of the Vatican City State since 13 March 2013. ...
points out, "the knowledge that comes from the Holy Spirit, however, is not limited to human knowledge; it is a special gift, which leads us to grasp, through creation, the greatness and love of God and his profound relationship with every creature." In
Islam Islam (; ar, ۘالِإسلَام, , ) is an Abrahamic monotheistic religion centred primarily around the Quran, a religious text considered by Muslims to be the direct word of God in Islam, God (or ''Allah'') as it was revealed to Muh ...
, knowledge (Arabic: علم, ''ʿilm'') is given great significance. "The Knowing" (''al-ʿAlīm'') is one of the 99 names reflecting distinct attributes of
God In monotheistic thought, God is usually viewed as the supreme being, creator, and principal object of faith. Swinburne, R.G. "God" in Honderich, Ted. (ed)''The Oxford Companion to Philosophy'', Oxford University Press, 1995. God is typicall ...
. The
Qur'an The Quran (, ; Standard Arabic: , Classical Arabic, Quranic Arabic: , , 'the recitation'), also romanized Qur'an or Koran, is the central religious text of Islam, believed by Muslims to be a revelation in Islam, revelation from God in Islam, ...
asserts that knowledge comes from God () and various ''
hadith Ḥadīth ( or ; ar, حديث, , , , , , , literally "talk" or "discourse") or Athar ( ar, أثر, , literally "remnant"/"effect") refers to what the majority of Muslims believe to be a record of the words, actions, and the silent approva ...
'' encourage the acquisition of knowledge.
Muhammad Muhammad ( ar, مُحَمَّد;  570 – 8 June 632 Common Era, CE) was an Arab religious, social, and political leader and the founder of Islam. According to Muhammad in Islam, Islamic doctrine, he was a prophet Divine inspiration, di ...
is reported to have said "Seek knowledge from the cradle to the grave" and "Verily the men of knowledge are the inheritors of the prophets". Islamic scholars, theologians and jurists are often given the title ''
alim Alim (''ʿAlīm'' , also anglicized as ''Aleem'') is one of the Names of God in Islam, meaning "''All-knowing one''". It is also used as a personal name, as a short form of Abdul Alim, "''Servant of the All-Knowing''": Given name * Alimuddin Ahma ...
'', meaning "knowledgeble". In
Gnostic Gnosticism (from grc, γνωστικός, gnōstikós, , 'having knowledge') is a collection of religious ideas and systems which coalesced in the late 1st century AD among Judaism, Jewish and Early Christianity, early Christian sects. These ...
beliefs, everyone is said to possess a piece of the highest good or Ultimate God deep within themselves that had fallen from the spiritual world into the bodies of humans, sometimes called a
divine spark The divine spark is a term used in various different religious traditions. Gnosticism In Gnosticism Gnosticism (from grc, γνωστικός, gnōstikós, , 'having knowledge') is a collection of religious ideas and systems which coalesced ...
. It is trapped in their material bodies created by the inferior God or
Demiurge In the Platonism, Platonic, Neopythagorean, Middle Platonism, Middle Platonic, and Neoplatonism, Neoplatonic schools of philosophy, the demiurge () is an artisan-like figure responsible for fashioning and maintaining the physical universe. The G ...
unless secret knowledge from the outside universe called
gnosis Gnosis is the common Greek language, Greek noun for knowledge (wikt:γνῶσις, γνῶσις, ''gnōsis'', f.). The term was used among various Hellenistic religions and Hellenistic philosophy, philosophies in the Greco-Roman world. It is b ...
is achieved. The one who brings such knowledge is considered the savior or redeemer.
Hindu Hindus (; ) are people who religiously adhere to Hinduism.Jeffery D. Long (2007), A Vision for Hinduism, IB Tauris, , pages 35–37 Historically, the term has also been used as a geographical, cultural, and later religious identifier for ...
Scriptures present two kinds of knowledge, ''Paroksh Gyan'' and ''Prataksh Gyan''. ''Paroksh Gyan'' (also spelled '' Paroksha-Jnana'') is secondhand knowledge: knowledge obtained from books, hearsay, etc. ''Pratyaksh Gyan'' (also spelled ''Pratyaksha-Jnana'') is the knowledge borne of direct experience, i.e., knowledge that one discovers for oneself. Knowledge is of special importance in the classical path of Hinduism known as ''
jnana yoga Jnana yoga (), also known as the jnana ''marga'' (), is one of the Three Yogas , three classical paths (''Spirituality#Hinduism , margas'') for moksha (liberation) in Hinduism, which emphasizes the "path of knowledge", also known as the "path ...
'' or ''path of knowledge''. Its aim is to achieve oneness with the divine by fostering an understanding of the
self The self is an individual as the object of that individual’s own reflective consciousness. Since the ''self'' is a reference by a subject to the same subject, this reference is necessarily Subjective character of experience, subjective. The sen ...
and its relation to
Brahman In Hinduism, ''Brahman'' ( sa, ब्रह्मन्) connotes the highest universal principle, the ultimate reality in the universe The universe is all of space and time and their contents, including planets, stars, galaxy, ga ...
or ultimate reality. According to the
Jain Jainism ( ), also known as Jain Dharma, is an Indian religions, Indian religion. Jainism traces its spiritual ideas and history through the succession of twenty-four tirthankaras (supreme preachers of ''Dharma''), with the first in the current ...
texts like Tattvārthsūtra and Sarvārthasiddhi, there are five kinds of knowledge: sensory knowledge, scriptural knowledge, clairvoyance, telepathy, and omniscience (Mati Jñāna, Śruta Jñāna, Avadhi Jñāna, Manah prayāya, and Kevala Jnana). The first two kinds are regarded as indirect knowledge since the soul depends on the sense and the mind to acquire them. This is not the case for the remaining three kinds, which constitute direct knowledge.


Anthropology

The ''anthropology of knowledge'' is a multi-disciplinary field of inquiry. It studies how knowledge is acquired, stored, retrieved, and communicated. Special interest is given to how knowledge is reproduced and undergoes changes in relation to social and cultural circumstances. In this context, the term ''knowledge'' is used in a very broad sense, roughly equivalent to terms like ''understanding'' and ''
culture Culture () is an umbrella term which encompasses the social behavior, institutions, and Social norm, norms found in human Society, societies, as well as the knowledge, beliefs, arts, laws, Social norm, customs, capabilities, and habits of the ...
''. This means that the forms and reproduction of understanding are studied irrespective of their
truth value In logic Logic is the study of correct reasoning. It includes both Mathematical logic, formal and informal logic. Formal logic is the science of Validity (logic), deductively valid inferences or of logical truths. It is a formal science in ...
. In epistemology, on the other hand, knowledge is usually restricted to forms of true belief. The main focus in
anthropology Anthropology is the scientific study of humanity, concerned with human behavior, human biology, cultures, societies, and linguistics Linguistics is the scientific study of human language. It is called a scientific study because i ...
is on empirical observations of how people ascribe truth values to meaning contents, like when affirming an assertion, even if these contents are false. But it also includes practical components: knowledge is what is employed when interpreting and acting on the world and involves diverse phenomena, such as feelings, embodied skills, information, and concepts. It is used to understand and anticipate events in order to prepare and react accordingly. The reproduction of knowledge and its changes often happen through some form of
communication Communication (from la, communicare, meaning "to share" or "to be in relation with") is usually defined as the transmission of information. The term may also refer to the message communicated through such transmissions or the field of inquir ...
. This includes face-to-face discussions and online communications as well as seminars and rituals. An important role in this context falls to
institution Institutions are humanly devised structures of rules and norms that shape and constrain individual behavior. All definitions of institutions generally entail that there is a level of persistence and continuity. Laws, rules, social conventions a ...
s, like university departments or scientific journals in the academic context. A ''
tradition A tradition is a belief or behavior (folk custom) passed down within a group or society A society is a group of individuals involved in persistent social interaction, or a large social group sharing the same spatial or social territo ...
'' may be defined as knowledge that has been reproduced within a
society A society is a group of individuals involved in persistent social interaction, or a large social group sharing the same spatial or social territory, typically subject to the same political Politics (from , ) is the set of activitie ...
or geographic region over several generations. However, societies also respond to various external influences, such as other societies, whose understanding is often interpreted and incorporated in a modified form. An important finding is that individuals belonging to the same social group usually understand things and organize knowledge in similar ways to one another. In this regard, social identities play a significant role: individuals who associate themselves with similar identities, like age-influenced, professional, religious, and ethnic identities, tend to embody similar forms of knowledge.


See also

* Outline of knowledgeguide to the subject of knowledge presented as a
tree structure A tree structure, tree diagram, or tree model is a way of representing the hierarchy, hierarchical nature of a structure in a graphical form. It is named a "tree structure" because the classic #Representing trees, representation resembles a tree ...
d list of its subtopics *
Outline of human intelligence The following Outline (list), outline is provided as an overview of and topical guide to human intelligence: Intelligence#Human intelligence, Human intelligence is, in the Homo sapiens, human species, the mental capacities to learn, understand, ...
*
Decolonization of knowledge Decolonization of knowledge (also epistemic decolonization or epistemological decolonization) is a concept advanced in Decoloniality, decolonial scholarship that critiques the perceived hegemony of Western knowledge systems. It seeks to construc ...
*
Desacralization of knowledge In Tradition (perennialism), traditionalist philosophy, desacralization of knowledge or secularization of knowledge is the process of separation of knowledge from its Divinity, divine source—God or the Ultimate Reality. The process reflects a p ...
*
Epistemic modal logic Epistemic modal logic is a subfield of modal logic that is concerned with reasoning about knowledge. While epistemology has a long philosophical tradition dating back to Ancient Greece, epistemic logic is a much more recent development with applica ...
*
Inductive inference Inductive reasoning is a method of reasoning in which a general principle is derived from a body of observations. It consists of making broad generalizations based on specific observations. Inductive reasoning is distinct from Deductive reasonin ...
* Inductive probability *
Intelligence Intelligence has been defined in many ways: the capacity for abstraction, logic, understanding, self-awareness, learning Learning is the process of acquiring new understanding, knowledge, behaviors, skills, value (personal and cultura ...
*
Knowledge transfer Knowledge transfer is the sharing or disseminating of knowledge and the providing of inputs to problem solving Problem solving is the process of achieving a goal by overcoming obstacles, a frequent part of most activities. Problems in nee ...
* Metaknowledge *
Omniscience Omniscience () is the capacity to know everything. In Hinduism, Sikhism and the Abrahamic religions The Abrahamic religions are a group of religions centered around worship of the God in Abrahamic religions, God of Abraham. Abraham, ...


References


Notes


Citations


Bibliography

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External links

* * * * * * {{Authority control
Knowledge Knowledge can be defined as Descriptive knowledge, awareness of facts or as Procedural knowledge, practical skills, and may also refer to Knowledge by acquaintance, familiarity with objects or situations. Knowledge of facts, also called pro ...
Concepts in epistemology Intelligence Mental content Virtue Main topic articles