Method Of Reasoning
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Reason is the capacity of consciously applying
logic Logic is the study of correct reasoning. It includes both formal and informal logic. Formal logic is the science of deductively valid inferences or of logical truths. It is a formal science investigating how conclusions follow from premises ...
by drawing conclusions from new or existing
information Information is an abstract concept that refers to that which has the power to inform. At the most fundamental level information pertains to the interpretation of that which may be sensed. Any natural process that is not completely random ...
, with the aim of seeking the
truth Truth is the property of being in accord with fact or reality.Merriam-Webster's Online Dictionarytruth 2005 In everyday language, truth is typically ascribed to things that aim to represent reality or otherwise correspond to it, such as beliefs ...
. It is closely associated with such characteristically
human Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...
activities as
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 ...
,
science Science is a systematic endeavor that builds and organizes knowledge in the form of testable explanations and predictions about the universe. Science may be as old as the human species, and some of the earliest archeological evidence for ...
,
language Language is a structured system of communication. The structure of a language is its grammar and the free components are its vocabulary. Languages are the primary means by which humans communicate, and may be conveyed through a variety of met ...
,
mathematics 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 ...
, and
art Art is a diverse range of human activity, and resulting product, that involves creative or imaginative talent expressive of technical proficiency, beauty, emotional power, or conceptual ideas. There is no generally agreed definition of wha ...
, and is normally considered to be a distinguishing ability possessed by
humans Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...
. Reason is sometimes referred to as
rationality Rationality is the quality of being guided by or based on reasons. In this regard, a person acts rationally if they have a good reason for what they do or a belief is rational if it is based on strong evidence. This quality can apply to an abil ...
. Reasoning is associated with the acts of
thinking 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 ...
and cognition, and involves the use of one's intellect. The field of
logic Logic is the study of correct reasoning. It includes both formal and informal logic. Formal logic is the science of deductively valid inferences or of logical truths. It is a formal science investigating how conclusions follow from premises ...
studies the ways in which humans can use formal reasoning to produce logically valid
argument An argument is a statement or group of statements called premises intended to determine the degree of truth or acceptability of another statement called conclusion. Arguments can be studied from three main perspectives: the logical, the dialectic ...
s. Reasoning may be subdivided into
forms Form is the shape, visual appearance, or configuration of an object. In a wider sense, the form is the way something happens. Form also refers to: *Form (document), a document (printed or electronic) with spaces in which to write or enter data * ...
of
logical reasoning Two kinds of logical reasoning are often distinguished in addition to formal deduction: induction and abduction. Given a precondition or ''premise'', a conclusion or ''logical consequence'' and a rule or ''material conditional'' that implies the ...
, such as: deductive reasoning, inductive reasoning, and abductive reasoning.
Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of phil ...
drew a distinction between logical discursive reasoning (reason proper), and intuitive reasoning, in which the reasoning process through intuition—however valid—may tend toward the personal and the subjectively opaque. In some social and political settings logical and intuitive modes of reasoning may clash, while in other contexts intuition and formal reason are seen as complementary rather than adversarial. For example, in
mathematics 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 ...
, intuition is often necessary for the creative processes involved with arriving at a
formal proof In logic and mathematics, a formal proof or derivation is a finite sequence of sentences (called well-formed formulas in the case of a formal language), each of which is an axiom, an assumption, or follows from the preceding sentences in the seq ...
, arguably the most difficult of formal reasoning tasks. Reasoning, like habit or
intuition Intuition is the ability to acquire knowledge without recourse to conscious reasoning. Different fields use the word "intuition" in very different ways, including but not limited to: direct access to unconscious knowledge; unconscious cognition; ...
, is one of the ways by which thinking moves from one idea to a related idea. For example, reasoning is the means by which rational individuals understand sensory information from their environments, or conceptualize abstract dichotomies such as cause and
effect Effect may refer to: * A result or change of something ** List of effects ** Cause and effect, an idiom describing causality Pharmacy and pharmacology * Drug effect, a change resulting from the administration of a drug ** Therapeutic effect, a ...
,
truth Truth is the property of being in accord with fact or reality.Merriam-Webster's Online Dictionarytruth 2005 In everyday language, truth is typically ascribed to things that aim to represent reality or otherwise correspond to it, such as beliefs ...
and
falsehood Deception or falsehood is an act or statement that misleads, hides the truth, or promotes a belief, concept, or idea that is not true. It is often done for personal gain or advantage. Deception can involve dissimulation, propaganda and sleight o ...
, or ideas regarding notions of good or evil. Reasoning, as a part of executive decision making, is also closely identified with the ability to self-consciously change, in terms of
goal A goal is an idea of the future or desired result that a person or a group of people envision, plan and commit to achieve. People endeavour to reach goals within a finite time by setting deadlines. A goal is roughly similar to a purpose or ...
s,
belief A belief is an attitude that something is the case, or that some proposition is true. In epistemology, philosophers use the term "belief" to refer to attitudes about the world which can be either true or false. To believe something is to take ...
s, attitudes,
tradition A tradition is a belief or behavior (folk custom) passed down within a group or society with symbolic meaning or special significance with origins in the past. A component of cultural expressions and folklore, common examples include holidays or ...
s, and institutions, and therefore with the capacity for freedom and self-determination. In contrast to the use of "reason" as an abstract noun, a reason is a consideration given which either explains or justifies events, phenomena, or behavior.Merriam-Webster.com
Merriam-Webster Dictionary definition of reason
Reasons justify decisions, reasons support explanations of natural phenomena; reasons can be given to explain the actions (conduct) of individuals. Using reason, or reasoning, can also be described more plainly as providing good, or the best, reasons. For example, when evaluating a moral decision, "morality is, at the very least, the effort to guide one's conduct by ''reason''—that is, doing what there are the best reasons for doing—while giving equal nd impartialweight to the interests of all those affected by what one does." Psychologists and
cognitive scientists 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, attention, thought, ...
have attempted to study and explain how people reason, e.g. which cognitive and neural processes are engaged, and how cultural factors affect the inferences that people draw. The field of
automated reasoning In computer science, in particular in knowledge representation and reasoning and metalogic, the area of automated reasoning is dedicated to understanding different aspects of reasoning. The study of automated reasoning helps produce computer prog ...
studies how reasoning may or may not be modeled computationally.
Animal psychology Comparative psychology refers to the scientific study of the behavior and mental processes of non-human animals, especially as these relate to the phylogenetic history, adaptive significance, and development of behavior. Research in this area addr ...
considers the question of whether animals other than humans can reason.


Etymology and related words

In the
English language English is a West Germanic language of the Indo-European language family, with its earliest forms spoken by the inhabitants of early medieval England. It is named after the Angles, one of the ancient Germanic peoples that migrated to the is ...
and other modern
European languages Most languages of Europe belong to the Indo-European language family. Out of a total European population of 744 million as of 2018, some 94% are native speakers of an Indo-European language. Within Indo-European, the three largest phyla are Ro ...
, "reason", and related words, represent words which have always been used to translate Latin and classical Greek terms in the sense of their philosophical usage. * The original
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
term was ''
logos ''Logos'' (, ; grc, λόγος, lógos, lit=word, discourse, or reason) is a term used in Western philosophy, psychology and rhetoric and refers to the appeal to reason that relies on logic or reason, inductive and deductive reasoning. Ari ...
'', the root of the modern English word "
logic Logic is the study of correct reasoning. It includes both formal and informal logic. Formal logic is the science of deductively valid inferences or of logical truths. It is a formal science investigating how conclusions follow from premises ...
" but also a word which could mean for example "speech" or "explanation" or an "account" (of money handled). * As a philosophical term ''logos'' was translated in its non-linguistic senses in
Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
as ''
ratio In mathematics, a ratio shows how many times one number contains another. For example, if there are eight oranges and six lemons in a bowl of fruit, then the ratio of oranges to lemons is eight to six (that is, 8:6, which is equivalent to the ...
''. This was originally not just a translation used for philosophy, but was also commonly a translation for ''logos'' in the sense of an account of money. * French '' raison'' is derived directly from Latin, and this is the direct source of the English word "reason". The earliest major philosophers to publish in English, such as
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 and Lord Chancellor of England. Bacon led the advancement of both ...
,
Thomas Hobbes Thomas Hobbes ( ; 5/15 April 1588 – 4/14 December 1679) was an English philosopher, considered to be one of the founders of modern political philosophy. Hobbes is best known for his 1651 book ''Leviathan'', in which he expounds an influ ...
, and
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 Enlightenment, Enlightenment thinkers and commonly known as the "father of liberalism ...
also routinely wrote in Latin and French, and compared their terms to Greek, treating the words "''logos''", "''ratio''", "''raison''" and "reason" as interchangeable. The meaning of the word "reason" in senses such as "human reason" also overlaps to a large extent with "
rationality Rationality is the quality of being guided by or based on reasons. In this regard, a person acts rationally if they have a good reason for what they do or a belief is rational if it is based on strong evidence. This quality can apply to an abil ...
" and the adjective of "reason" in philosophical contexts is normally "
rational Rationality is the quality of being guided by or based on reasons. In this regard, a person acts rationally if they have a good reason for what they do or a belief is rational if it is based on strong evidence. This quality can apply to an abi ...
", rather than "reasoned" or "reasonable". Some philosophers,
Thomas Hobbes Thomas Hobbes ( ; 5/15 April 1588 – 4/14 December 1679) was an English philosopher, considered to be one of the founders of modern political philosophy. Hobbes is best known for his 1651 book ''Leviathan'', in which he expounds an influ ...
for example, also used the word ratiocination as a synonym for "reasoning".


Philosophical history

The proposal that reason gives humanity a special position in nature has been argued to be a defining characteristic of western
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 ...
and later western modern science, starting with classical Greece. Philosophy can be described as a way of life based upon reason, and in the other direction, reason has been one of the major subjects of philosophical discussion since ancient times. Reason is often said to be reflexive, or "self-correcting", and the critique of reason has been a persistent theme in philosophy. It has been defined in different ways, at different times, by different thinkers about human nature.


Classical philosophy

For many classical
philosophers A philosopher is a person who practices or investigates philosophy. The term ''philosopher'' comes from the grc, φιλόσοφος, , translit=philosophos, meaning 'lover of wisdom'. The coining of the term has been attributed to the Greek th ...
, nature was understood teleologically, meaning that every type of thing had a definitive purpose that fit within a natural order that was itself understood to have aims. Perhaps starting with
Pythagoras Pythagoras of Samos ( grc, Πυθαγόρας ὁ Σάμιος, Pythagóras ho Sámios, Pythagoras the Samos, Samian, or simply ; in Ionian Greek; ) was an ancient Ionians, Ionian Ancient Greek philosophy, Greek philosopher and the eponymou ...
or
Heraclitus Heraclitus of Ephesus (; grc-gre, Ἡράκλειτος , "Glory of Hera"; ) was an ancient Greek pre-Socratic philosopher from the city of Ephesus, which was then part of the Persian Empire. Little is known of Heraclitus's life. He wrote ...
, the
cosmos The cosmos (, ) is another name for the Universe. Using the word ''cosmos'' implies viewing the universe as a complex and orderly system or entity. The cosmos, and understandings of the reasons for its existence and significance, are studied in ...
is even said to have reason. Reason, by this account, is not just one characteristic that humans happen to have, and that influences happiness amongst other characteristics. Reason was considered of higher stature than other characteristics of human nature, such as sociability, because it is something humans share with nature itself, linking an apparently immortal part of the human mind with the divine order of the cosmos itself. Within the human mind or
soul In many religious and philosophical traditions, there is a belief that a soul is "the immaterial aspect or essence of a human being". Etymology The Modern English noun ''soul'' is derived from Old English ''sāwol, sāwel''. The earliest attes ...
(''
psyche Psyche (''Psyché'' in French) is the Greek term for "soul" (ψυχή). Psyche may also refer to: Psychology * Psyche (psychology), the totality of the human mind, conscious and unconscious * ''Psyche'', an 1846 book about the unconscious by Car ...
''), reason was described by
Plato Plato ( ; grc-gre, Πλάτων ; 428/427 or 424/423 – 348/347 BC) was a Greek philosopher born in Athens during the Classical period in Ancient Greece. He founded the Platonist school of thought and the Academy, the first institution ...
as being the natural monarch which should rule over the other parts, such as spiritedness (''
thumos ''Thumos'' (also commonly spelled 'thymos'; grc-gre, θυμός) is the Ancient Greek concept of "spiritedness" (as in "a spirited stallion" or "spirited debate"). The word indicates a physical association with breath or blood and is also used to ...
'') and the passions.
Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of phil ...
, Plato's student, defined human beings as
rational animal The term rational animal (Latin: ''animal rationale'' or ''animal rationabile'') refers to a classical definition of humanity or human nature, associated with Aristotelianism. History While the Latin term itself originates in scholasticism, it r ...
s, emphasizing reason as a characteristic of
human nature Human nature is a concept that denotes the fundamental dispositions and characteristics—including ways of thinking, feeling, and acting—that humans are said to have naturally. The term is often used to denote the essence of humankind, or ...
. He ''defined'' the highest human happiness or well being ('' eudaimonia'') as a life which is lived consistently, excellently, and completely in accordance with reason. The conclusions to be drawn from the discussions of Aristotle and Plato on this matter are amongst the most debated in the history of philosophy., p. 3. But teleological accounts such as Aristotle's were highly influential for those who attempt to explain reason in a way that is consistent with
monotheism Monotheism is the belief that there is only one deity, an all-supreme being that is universally referred to as God. Cross, F.L.; Livingstone, E.A., eds. (1974). "Monotheism". The Oxford Dictionary of the Christian Church (2 ed.). Oxford: Oxfo ...
and the immortality and divinity of the human soul. For example, in the
neoplatonist Neoplatonism is a strand of Platonic philosophy that emerged in the 3rd century AD against the background of Hellenistic philosophy and religion. The term does not encapsulate a set of ideas as much as a chain of thinkers. But there are some id ...
account of
Plotinus Plotinus (; grc-gre, Πλωτῖνος, ''Plōtînos'';  – 270 CE) was a philosopher in the Hellenistic tradition, born and raised in Roman Egypt. Plotinus is regarded by modern scholarship as the founder of Neoplatonism. His teacher wa ...
, the
cosmos The cosmos (, ) is another name for the Universe. Using the word ''cosmos'' implies viewing the universe as a complex and orderly system or entity. The cosmos, and understandings of the reasons for its existence and significance, are studied in ...
has one soul, which is the seat of all reason, and the souls of all individual humans are part of this soul. Reason is for Plotinus both the provider of form to material things, and the light which brings individuals souls back into line with their source.


Christian and Islamic philosophy

The classical view of reason, like many important Neoplatonic and Stoic ideas, was readily adopted by the early Church as the Church Fathers saw Greek Philosophy as an indispensable instrument given to mankind so that we may understand revelation. For example, the greatest among the early saint Church Fathers and
Doctors of the Church Doctor of the Church (Latin: ''doctor'' "teacher"), also referred to as Doctor of the Universal Church (Latin: ''Doctor Ecclesiae Universalis''), is a title given by the Catholic Church to saints recognized as having made a significant contribu ...
such as Augustine of Hippo, Basil of Caesarea and
Gregory of Nyssa Gregory of Nyssa, also known as Gregory Nyssen ( grc-gre, Γρηγόριος Νύσσης; c. 335 – c. 395), was Bishop of Nyssa in Cappadocia from 372 to 376 and from 378 until his death in 395. He is venerated as a saint in Catholicis ...
were as much Neoplatonic philosophers as they were Christian theologians and adopted the Neoplatonic view of human reason together with the associated implications for our relationship to creation, to ourselves and to God. Such Neoplatonist accounts of the rational part of the human soul were also standard amongst medieval Islamic philosophers and remain important in
Iranian philosophy Iranian philosophy ( Persian: فلسفه ایرانی) or Persian philosophy can be traced back as far as to Old Iranian philosophical traditions and thoughts which originated in ancient Indo-Iranian roots and were considerably influenced by Zar ...
. As European intellectualism recovered from the post-Roman Dark Ages, the Christian Patristic heritage and the influence of the great Islamic scholars such as
Averroes Ibn Rushd ( ar, ; full name in ; 14 April 112611 December 1198), often Latinized as Averroes ( ), was an Andalusian polymath and jurist who wrote about many subjects, including philosophy, theology, medicine, astronomy, physics, psy ...
and Avicenna produced the Scholastic (see Scholasticism) view of reason from which our modern idea of this concept has developed. Among the Scholastics who relied on the classical concept of reason for the development of their doctrines, none were more influential than Saint Thomas Aquinas, who put this concept at the heart of his
Natural Law Natural law ( la, ius naturale, ''lex naturalis'') is a system of law based on a close observation of human nature, and based on values intrinsic to human nature that can be deduced and applied independently of positive law (the express enacte ...
. In this doctrine, Thomas concludes that because humans have reason and because reason is a spark of the divine, every single human life is invaluable, all humans are equal and every human is born with an intrinsic and permanent set of basic rights. On this foundation, the idea of human rights would later be constructed by Spanish theologians at the
School of Salamanca The School of Salamanca ( es, Escuela de Salamanca) is the Renaissance of thought in diverse intellectual areas by Spanish theologians, rooted in the intellectual and pedagogical work of Francisco de Vitoria. From the beginning of the 16th cen ...
. Other Scholastics, such as Roger Bacon and
Albertus Magnus Albertus Magnus (c. 1200 – 15 November 1280), also known as Saint Albert the Great or Albert of Cologne, was a German Dominican friar, philosopher, scientist, and bishop. Later canonised as a Catholic saint, he was known during his li ...
, following the example of Islamic scholars such as
Alhazen Ḥasan Ibn al-Haytham, Latinized as Alhazen (; full name ; ), was a medieval mathematician, astronomer, and physicist of the Islamic Golden Age from present-day Iraq.For the description of his main fields, see e.g. ("He is one of the prin ...
, emphasised reason an intrinsic human ability to decode the created order and the structures that underlie our experienced physical reality. This interpretation of reason was instrumental to the development of the scientific method in the early Universities of the high Middle Ages.


Subject-centred reason in early modern philosophy

The early modern era was marked by a number of significant changes in the understanding of reason, starting in
Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
. One of the most important of these changes involved a change in the
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 ...
understanding of human beings. Scientists and philosophers began to question the teleological understanding of the world. Nature was no longer assumed to be human-like, with its own aims or reason, and human nature was no longer assumed to work according to anything other than the same " laws of nature" which affect inanimate things. This new understanding eventually displaced the previous
world view A worldview or world-view or ''Weltanschauung'' is the fundamental cognitive orientation of an individual or society encompassing the whole of the individual's or society's knowledge, culture, and point of view. A worldview can include natural ...
that derived from a spiritual understanding of the universe. Accordingly, in the 17th century,
René Descartes René Descartes ( or ; ; Latinized: Renatus Cartesius; 31 March 1596 – 11 February 1650) was a French philosopher, scientist, and mathematician, widely considered a seminal figure in the emergence of modern philosophy and science. Mathem ...
explicitly rejected the traditional notion of humans as "rational animals", suggesting instead that they are nothing more than "thinking things" along the lines of other "things" in nature. Any grounds of knowledge outside that understanding was, therefore, subject to doubt. In his search for a foundation of all possible knowledge, Descartes deliberately decided to throw into doubt ''all'' knowledge – ''except'' that of the mind itself in the process of thinking:
At this time I admit nothing that is not necessarily true. I am therefore precisely nothing but a thinking thing; that is a mind, or intellect, or understanding, or reason – words of whose meanings I was previously ignorant.
This eventually became known as epistemological or "subject-centred" reason, because it is based on the ''knowing subject'', who perceives the rest of the world and itself as a set of objects to be studied, and successfully mastered by applying the knowledge accumulated through such study. Breaking with tradition and many thinkers after him, Descartes explicitly did not divide the incorporeal soul into parts, such as reason and intellect, describing them as one indivisible incorporeal entity. A contemporary of Descartes,
Thomas Hobbes Thomas Hobbes ( ; 5/15 April 1588 – 4/14 December 1679) was an English philosopher, considered to be one of the founders of modern political philosophy. Hobbes is best known for his 1651 book ''Leviathan'', in which he expounds an influ ...
described reason as a broader version of "addition and subtraction" which is not limited to numbers. This understanding of reason is sometimes termed "calculative" reason. Similar to Descartes, Hobbes asserted that "No discourse whatsoever, can end in absolute knowledge of fact, past, or to come" but that "sense and memory" is absolute knowledge. In the late 17th century, through the 18th century,
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 Enlightenment, Enlightenment thinkers and commonly known as the "father of liberalism ...
and
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 999br>David Hume" ''Encyclopædia Britannica''. Retrieved 18 May 2020. was a Scottish Enlightenment phil ...
developed Descartes's line of thought still further. Hume took it in an especially
skeptical Skepticism, also spelled scepticism, is a questioning attitude or doubt toward knowledge claims that are seen as mere belief or dogma. For example, if a person is skeptical about claims made by their government about an ongoing war then the p ...
direction, proposing that there could be no possibility of deducing relationships of cause and effect, and therefore no knowledge is based on reasoning alone, even if it seems otherwise. Hume famously remarked that, "We speak not strictly and philosophically when we talk of the combat of passion and of reason. Reason is, and ought only to be the slave of the passions, and can never pretend to any other office than to serve and obey them." Hume also took his definition of reason to unorthodox extremes by arguing, unlike his predecessors, that human reason is not qualitatively different from either simply conceiving individual ideas, or from judgments associating two ideas, and that "reason is nothing but a wonderful and unintelligible instinct in our souls, which carries us along a certain train of ideas, and endows them with particular qualities, according to their particular situations and relations." It followed from this that animals have reason, only much less complex than human reason. In the 18th century,
Immanuel Kant Immanuel Kant (, , ; 22 April 1724 – 12 February 1804) was a German philosopher and one of the central Enlightenment thinkers. Born in Königsberg, Kant's comprehensive and systematic works in epistemology, metaphysics, ethics, and ...
attempted to show that Hume was wrong by demonstrating that a " transcendental" self, or "I", was a necessary condition of all experience. Therefore, suggested Kant, on the basis of such a self, it is in fact possible to reason both about the conditions and limits of human knowledge. And so long as these limits are respected, reason can be the vehicle of morality, justice, aesthetics, theories of knowledge (
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. Episte ...
), and understanding.


Substantive and formal reason

In the formulation of Kant, who wrote some of the most influential modern treatises on the subject, the great achievement of reason (german: Vernunft) is that it is able to exercise a kind of universal law-making. Kant was able therefore to reformulate the basis of moral-practical, theoretical and aesthetic reasoning, on "universal" laws. Here
practical reason In philosophy, practical reason is the use of reason to decide how to act. It contrasts with theoretical reason, often called speculative reason, the use of reason to decide what to follow. For example, agents use practical reason to decide whethe ...
ing is the self-legislating or self-governing formulation of universal norms, and
theoretical A theory is a rational type of abstract thinking about a phenomenon, or the results of such thinking. The process of contemplative and rational thinking is often associated with such processes as observational study or research. Theories may be ...
reasoning the way humans posit universal laws of nature. Under practical reason, the moral autonomy or freedom of human beings depends on their ability to behave according to laws that are given to them by the proper exercise of that reason. This contrasted with earlier forms of morality, which depended on religious understanding and interpretation, or
nature Nature, in the broadest sense, is the physics, physical world or universe. "Nature" can refer to the phenomenon, phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. ...
for their substance. According to Kant, in a free society each individual must be able to pursue their goals however they see fit, so long as their actions conform to principles given by reason. He formulated such a principle, called the "
categorical imperative The categorical imperative (german: kategorischer Imperativ) is the central philosophical concept in the deontological moral philosophy of Immanuel Kant. Introduced in Kant's 1785 '' Groundwork of the Metaphysic of Morals'', it is a way of eva ...
", which would justify an action only if it could be universalized:
Act only according to that maxim whereby you can, at the same time, will that it should become a universal law.
In contrast to Hume then, Kant insists that reason itself (German '' Vernunft'') has natural ends, the solution to the metaphysical problems, especially the discovery of the foundations of morality. Kant claimed that this problem could be solved with his " transcendental logic" which unlike normal logic is not just an instrument, which can be used indifferently, as it was for Aristotle, but a theoretical science in its own right and the basis of all the others. According to Jürgen Habermas, the "substantive unity" of reason has dissolved in modern times, such that it can no longer answer the question "How should I live?" Instead, the unity of reason has to be strictly formal, or "procedural". He thus described reason as a group of three autonomous spheres (on the model of Kant's three critiques): # ''Cognitive–instrumental reason'' is the kind of reason employed by the sciences. It is used to observe events, to predict and control outcomes, and to intervene in the world on the basis of its hypotheses; # ''Moral–practical reason'' is what we use to deliberate and discuss issues in the moral and political realm, according to universalizable procedures (similar to Kant's categorical imperative); and # ''Aesthetic reason'' is typically found in works of art and literature, and encompasses the novel ways of seeing the world and interpreting things that those practices embody. For Habermas, these three spheres are the domain of experts, and therefore need to be mediated with the "
lifeworld Lifeworld (or life-world) (german: Lebenswelt) may be conceived as a universe of what is self-evident or given, a world that subjects may experience together. The concept was popularized by Edmund Husserl, who emphasized its role as the ground o ...
" by philosophers. In drawing such a picture of reason, Habermas hoped to demonstrate that the substantive unity of reason, which in pre-modern societies had been able to answer questions about the good life, could be made up for by the unity of reason's formalizable procedures.


The critique of reason

Hamann, Herder,
Kant Immanuel Kant (, , ; 22 April 1724 – 12 February 1804) was a German philosopher and one of the central Enlightenment thinkers. Born in Königsberg, Kant's comprehensive and systematic works in epistemology, metaphysics, ethics, and aest ...
, Hegel, Kierkegaard,
Nietzsche Friedrich Wilhelm Nietzsche (; or ; 15 October 1844 – 25 August 1900) was a German philosopher, prose poet, cultural critic, philologist, and composer whose work has exerted a profound influence on contemporary philosophy. He began his car ...
,
Heidegger Martin Heidegger (; ; 26 September 188926 May 1976) was a German philosopher who is best known for contributions to phenomenology, hermeneutics, and existentialism. He is among the most important and influential philosophers of the 20th centur ...
, Foucault, Rorty, and many other philosophers have contributed to a debate about what reason means, or ought to mean. Some, like Kierkegaard, Nietzsche, and Rorty, are skeptical about subject-centred, universal, or instrumental reason, and even skeptical toward reason as a whole. Others, including Hegel, believe that it has obscured the importance of
intersubjectivity In philosophy, psychology, sociology, and anthropology, intersubjectivity is the relation or intersection between people's cognitive perspectives. Definition is a term coined by social scientists to refer to a variety of types of human interac ...
, or "spirit" in human life, and attempt to reconstruct a model of what reason should be. Some thinkers, e.g. Foucault, believe there are other ''forms'' of reason, neglected but essential to modern life, and to our understanding of what it means to live a life according to reason. In the last several decades, a number of proposals have been made to "re-orient" this critique of reason, or to recognize the "other voices" or "new departments" of reason: For example, in opposition to subject-centred reason, Habermas has proposed a model of communicative reason that sees it as an essentially cooperative activity, based on the fact of linguistic
intersubjectivity In philosophy, psychology, sociology, and anthropology, intersubjectivity is the relation or intersection between people's cognitive perspectives. Definition is a term coined by social scientists to refer to a variety of types of human interac ...
.
Nikolas Kompridis Nikolas Kompridis (; born 1953) is a Canadian philosopher and political theorist. His major published work addresses the direction and orientation of Frankfurt School critical theory; the legacy of philosophical romanticism; and the aesthetic ...
has proposed a widely encompassing view of reason as "that ensemble of practices that contributes to the opening and preserving of openness" in human affairs, and a focus on reason's possibilities for social change. The philosopher Charles Taylor, influenced by the 20th century German philosopher
Martin Heidegger Martin Heidegger (; ; 26 September 188926 May 1976) was a German philosopher who is best known for contributions to phenomenology, hermeneutics, and existentialism. He is among the most important and influential philosophers of the 20th ce ...
, has proposed that reason ought to include the faculty of
disclosure Disclosure may refer to: Arts and media * ''Disclosure'' (The Gathering album), 2012 *Disclosure (band), a UK-based garage/electronic duo * ''Disclosure'' (novel), 1994 novel written by Michael Crichton ** ''Disclosure'' (1994 film), an American ...
, which is tied to the way we make sense of things in everyday life, as a new "department" of reason. In the essay "What is Enlightenment?", Michel Foucault proposed a concept of critique based on Kant's distinction between "private" and "public" uses of reason. This distinction, as suggested, has two dimensions: * ''Private reason'' is the reason that is used when an individual is "a cog in a machine" or when one "has a role to play in society and jobs to do: to be a soldier, to have taxes to pay, to be in charge of a parish, to be a civil servant". * ''Public reason'' is the reason used "when one is reasoning as a reasonable being (and not as a cog in a machine), when one is reasoning as a member of reasonable humanity". In these circumstances, "the use of reason must be free and public."


Reason compared to related concepts


Compared to logic

The terms ''logic'' or ''logical'' are sometimes used as if they were identical with the term ''reason'' or with the concept of being ''rational'', or sometimes logic is seen as the most pure or the defining form of reason: "Logic is about reasoning—about going from premises to a conclusion. ... When you do logic, you try to clarify reasoning and separate good from bad reasoning." In modern
economics Economics () is the social science that studies the Production (economics), production, distribution (economics), distribution, and Consumption (economics), consumption of goods and services. Economics focuses on the behaviour and intera ...
,
rational choice Rational choice theory refers to a set of guidelines that help understand economic and social behaviour. The theory originated in the eighteenth century and can be traced back to political economist and philosopher, Adam Smith. The theory postula ...
is assumed to equate to logically
consistent In classical deductive logic, a consistent theory is one that does not lead to a logical contradiction. The lack of contradiction can be defined in either semantic or syntactic terms. The semantic definition states that a theory is consistent ...
choice. Reason and logic can however be thought of as distinct, although logic is one important aspect of reason. Author Douglas Hofstadter, in '' Gödel, Escher, Bach'', characterizes the distinction in this way: Logic is done inside a system while reason is done outside the system by such methods as skipping steps, working backward, drawing diagrams, looking at examples, or seeing what happens if you change the rules of the system. Psychologists Mark H. Bickard and Robert L. Campbell argued that "rationality cannot be simply assimilated to logicality"; they noted that "human knowledge of logic and logical systems has developed" over time through reasoning, and logical systems "can't construct new logical systems more powerful than themselves", so reasoning and rationality must involve more than a system of logic. Psychologist David Moshman, citing Bickhard and Campbell, argued for a " metacognitive conception of rationality" in which a person's development of reason "involves increasing consciousness and control of logical and other inferences". Reason is a type of thought, and
logic Logic is the study of correct reasoning. It includes both formal and informal logic. Formal logic is the science of deductively valid inferences or of logical truths. It is a formal science investigating how conclusions follow from premises ...
involves the attempt to describe a system of formal rules or norms of appropriate reasoning. The oldest surviving writing to explicitly consider the rules by which reason operates are the works of the
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
philosopher A philosopher is a person who practices or investigates philosophy. The term ''philosopher'' comes from the grc, φιλόσοφος, , translit=philosophos, meaning 'lover of wisdom'. The coining of the term has been attributed to the Greek th ...
Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of phil ...
, especially ''Prior Analysis'' and ''Posterior Analysis''. Although the Ancient Greeks had no separate word for logic as distinct from language and reason, Aristotle's newly coined word " syllogism" (''syllogismos'') identified logic clearly for the first time as a distinct field of study. When Aristotle referred to "the logical" (''hē logikē''), he was referring more broadly to rational thought.


Reason compared to cause-and-effect thinking, and symbolic thinking

As pointed out by philosophers such as Hobbes, Locke and Hume, some animals are also clearly capable of a type of " associative thinking", even to the extent of associating causes and effects. A dog once kicked, can learn how to recognize the warning signs and avoid being kicked in the future, but this does not mean the dog has reason in any strict sense of the word. It also does not mean that humans acting on the basis of experience or habit are using their reason. Human reason requires more than being able to associate two ideas, even if those two ideas might be described by a reasoning human as a cause and an effect, perceptions of smoke, for example, and memories of fire. For reason to be involved, the association of smoke and the fire would have to be thought through in a way which can be explained, for example as cause and effect. In the explanation of Locke, for example, reason requires the mental use of a third idea in order to make this comparison by use of syllogism. More generally, reason in the strict sense requires the ability to create and manipulate a system of symbols, as well as indices and icons, according to
Charles Sanders Peirce Charles Sanders Peirce ( ; September 10, 1839 – April 19, 1914) was an American philosopher, logician, mathematician and scientist who is sometimes known as "the father of pragmatism". Educated as a chemist and employed as a scientist for t ...
, the symbols having only a nominal, though habitual, connection to either smoke or fire. One example of such a system of artificial symbols and signs is
language Language is a structured system of communication. The structure of a language is its grammar and the free components are its vocabulary. Languages are the primary means by which humans communicate, and may be conveyed through a variety of met ...
. The connection of reason to symbolic thinking has been expressed in different ways by philosophers.
Thomas Hobbes Thomas Hobbes ( ; 5/15 April 1588 – 4/14 December 1679) was an English philosopher, considered to be one of the founders of modern political philosophy. Hobbes is best known for his 1651 book ''Leviathan'', in which he expounds an influ ...
described the creation of "Markes, or Notes of remembrance" (''
Leviathan Leviathan (; he, לִוְיָתָן, ) is a sea serpent noted in theology and mythology. It is referenced in several books of the Hebrew Bible, including Psalms, the Book of Job, the Book of Isaiah, the Book of Amos, and, according to some ...
'' Ch. 4) as ''speech''. He used the word ''speech'' as an English version of the Greek word ''
logos ''Logos'' (, ; grc, λόγος, lógos, lit=word, discourse, or reason) is a term used in Western philosophy, psychology and rhetoric and refers to the appeal to reason that relies on logic or reason, inductive and deductive reasoning. Ari ...
'' so that speech did not need to be communicated. When communicated, such speech becomes language, and the marks or notes or remembrance are called " Signes" by Hobbes. Going further back, although Aristotle is a source of the idea that only humans have reason (''logos''), he does mention that animals with imagination, for whom sense perceptions can persist, come closest to having something like reasoning and '' nous'', and even uses the word "logos" in one place to describe the distinctions which animals can perceive in such cases.


Reason, imagination, mimesis, and memory

Reason and
imagination Imagination is the production or simulation of novel objects, sensations, and ideas in the mind without any immediate input of the senses. Stefan Szczelkun characterises it as the forming of experiences in one's mind, which can be re-creations ...
rely on similar
mental processes 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, attention, thought, ...
. Imagination is not only found in humans. Aristotle, for example, stated that ''phantasia'' (imagination: that which can hold images or ''phantasmata'') and ''phronein'' (a type of thinking that can judge and understand in some sense) also exist in some animals. According to him, both are related to the primary perceptive ability of animals, which gathers the perceptions of different senses and defines the order of the things that are perceived without distinguishing universals, and without deliberation or ''logos''. But this is not yet reason, because human imagination is different. The recent modern writings of
Terrence Deacon Terrence William Deacon (born 1950) is an American neuroanthropologist (Ph.D. in Biological Anthropology, Harvard University 1984). He taught at Harvard for eight years, relocated to Boston University in 1992, and is currently Professor of Anth ...
and Merlin Donald, writing about the origin of language, also connect reason connected to not only
language Language is a structured system of communication. The structure of a language is its grammar and the free components are its vocabulary. Languages are the primary means by which humans communicate, and may be conveyed through a variety of met ...
, but also mimesis. More specifically they describe the ability to create
language Language is a structured system of communication. The structure of a language is its grammar and the free components are its vocabulary. Languages are the primary means by which humans communicate, and may be conveyed through a variety of met ...
as part of an internal modeling of
reality Reality is the sum or aggregate of all that is real or existent within a system, as opposed to that which is only imaginary. The term is also used to refer to the ontological status of things, indicating their existence. In physical terms, r ...
specific to humankind. Other results are
consciousness Consciousness, at its simplest, is sentience and awareness of internal and external existence. However, the lack of definitions has led to millennia of analyses, explanations and debates by philosophers, theologians, linguisticians, and scien ...
, and
imagination Imagination is the production or simulation of novel objects, sensations, and ideas in the mind without any immediate input of the senses. Stefan Szczelkun characterises it as the forming of experiences in one's mind, which can be re-creations ...
or
fantasy Fantasy is a genre of speculative fiction involving Magic (supernatural), magical elements, typically set in a fictional universe and sometimes inspired by mythology and folklore. Its roots are in oral traditions, which then became fantasy ...
. In contrast, modern proponents of a genetic predisposition to language itself include
Noam Chomsky Avram Noam Chomsky (born December 7, 1928) is an American public intellectual: a linguist, philosopher, cognitive scientist, historian, social critic, and political activist. Sometimes called "the father of modern linguistics", Chomsky is ...
and
Steven Pinker Steven Arthur Pinker (born September 18, 1954) is a Canadian-American cognitive psychologist, psycholinguist, popular science author, and public intellectual. He is an advocate of evolutionary psychology and the computational theory of mind. ...
, to whom Donald and Deacon can be contrasted. As reason is symbolic thinking, and peculiarly human, then this implies that humans have a special ability to maintain a clear consciousness of the distinctness of "icons" or images and the real things they represent. Starting with a modern author, Merlin Donald writes
A dog might perceive the "meaning" of a fight that was realistically play-acted by humans, but it could not reconstruct the message or distinguish the representation from its referent (a real fight). ..Trained apes are able to make this distinction; young children make this distinction early – hence, their effortless distinction between play-acting an event and the event itself
In classical descriptions, an equivalent description of this mental faculty is ''eikasia'', in the philosophy of Plato. This is the ability to perceive whether a perception is an image of something else, related somehow but not the same, and therefore allows humans to perceive that a dream or memory or a reflection in a mirror is not reality as such. What Klein refers to as ''dianoetic eikasia'' is the ''eikasia'' concerned specifically with thinking and mental images, such as those mental symbols, icons, ''signes'', and marks discussed above as definitive of reason. Explaining reason from this direction: human thinking is special in the way that we often understand visible things as if they were themselves images of our intelligible "objects of thought" as "foundations" (''hypothēses'' in Ancient Greek). This thinking (''dianoia'') is "...an activity which consists in making the vast and diffuse jungle of the visible world depend on a plurality of more 'precise' ''noēta''". Both Merlin Donald and the Socratic authors such as Plato and Aristotle emphasize the importance of ''mimesis'', often translated as ''imitation'' or ''representation''. Donald writes
Imitation is found especially in monkeys and apes .. but ...Mimesis is fundamentally different from imitation and mimicry in that it involves the invention of intentional representations. ..Mimesis is not absolutely tied to external communication.
''Mimēsis'' is a concept, now popular again in academic discussion, that was particularly prevalent in Plato's works, and within Aristotle, it is discussed mainly in the ''Poetics''. In Michael Davis's account of the theory of man in this work.
It is the distinctive feature of human action, that whenever we choose what we do, we imagine an action for ourselves as though we were inspecting it from the outside. Intentions are nothing more than imagined actions, internalizings of the external. All action is therefore imitation of action; it is poetic...
Donald like Plato (and Aristotle, especially in ''On Memory and Recollection''), emphasizes the peculiarity in humans of voluntary initiation of a search through one's mental world. The ancient Greek ''anamnēsis'', normally translated as "recollection" was opposed to ''mneme'' or ''memory''. Memory, shared with some animals, requires a consciousness not only of what happened in the past, but also ''that'' something happened in the past, which is in other words a kind of ''eikasia'' "...but nothing except man is able to recollect." Recollection is a deliberate effort to search for and recapture something once known. Klein writes that, "To become aware of our having forgotten something means to begin recollecting." Donald calls the same thing ''autocueing'', which he explains as follows: "Mimetic acts are reproducible on the basis of internal, self-generated cues. This permits voluntary recall of mimetic representations, without the aid of external cues – probably the earliest form of representational ''thinking''." In a celebrated paper in modern times, the fantasy author and philologist J.R.R. Tolkien wrote in his essay "On Fairy Stories" that the terms "fantasy" and "enchantment" are connected to not only "....the satisfaction of certain primordial human desires...." but also "...the origin of language and of the mind".


Logical reasoning methods and argumentation

A subdivision 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 ...
is
logic Logic is the study of correct reasoning. It includes both formal and informal logic. Formal logic is the science of deductively valid inferences or of logical truths. It is a formal science investigating how conclusions follow from premises ...
. Logic is the study of reasoning. Looking at logical categorizations of different types of reasoning, the traditional main division made in philosophy is between deductive reasoning and inductive reasoning.
Formal logic Logic is the study of correct reasoning. It includes both formal and informal logic. Formal logic is the science of deductively valid inferences or of logical truths. It is a formal science investigating how conclusions follow from premis ...
has been described as ''the science of deduction''. The study of inductive reasoning is generally carried out within the field known as informal logic or critical thinking.


Deductive reasoning

Deduction is a form of reasoning in which a conclusion follows necessarily from the stated premises. A deduction is also the conclusion reached by a deductive reasoning process. One classic example of deductive reasoning is that found in syllogisms like the following: * Premise 1: All humans are mortal. * Premise 2: Socrates is a human. * Conclusion: Socrates is mortal. The reasoning in this argument is deductively valid because there is no way in which the premises, 1 and 2, could be true and the conclusion, 3, be false.


Inductive reasoning

Induction is a form of inference producing propositions about unobserved objects or types, either specifically or generally, based on previous observation. It is used to ascribe properties or relations to objects or
types Type may refer to: Science and technology Computing * Typing, producing text via a keyboard, typewriter, etc. * Data type In computer science and computer programming, a data type (or simply type) is a set of possible values and a set of allo ...
based on previous observations or experiences, or to formulate general statements or
laws Law is a set of rules that are created and are enforceable by social or governmental institutions to regulate behavior,Robertson, ''Crimes against humanity'', 90. with its precise definition a matter of longstanding debate. It has been vari ...
based on limited observations of recurring phenomenal patterns. Inductive reasoning contrasts strongly with deductive reasoning in that, even in the best, or strongest, cases of inductive reasoning, the truth of the premises does not guarantee the truth of the conclusion. Instead, the conclusion of an inductive argument follows with some degree of
probability Probability is the branch of mathematics concerning numerical descriptions of how likely an Event (probability theory), event is to occur, or how likely it is that a proposition is true. The probability of an event is a number between 0 and ...
. Relatedly, the conclusion of an inductive argument contains more information than is already contained in the premises. Thus, this method of reasoning is ampliative. A classic example of inductive reasoning comes from the
empiricist In philosophy, empiricism is an epistemological theory that holds that knowledge or justification comes only or primarily from sensory experience. It is one of several views within epistemology, along with rationalism and skepticism. Empir ...
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 999br>David Hume" ''Encyclopædia Britannica''. Retrieved 18 May 2020. was a Scottish Enlightenment phil ...
: * Premise: The sun has risen in the east every morning up until now. * Conclusion: The sun will also rise in the east tomorrow.


Analogical reasoning

Analogical reasoning is a form of inductive reasoning from a particular to a particular. It is often used in
case-based reasoning In artificial intelligence and philosophy, case-based reasoning (CBR), broadly construed, is the process of solving new problems based on the solutions of similar past problems. In everyday life, an auto mechanic who fixes an engine by recallin ...
, especially legal reasoning. An example follows: * Premise 1: Socrates is human and mortal. * Premise 2: Plato is human. * Conclusion: Plato is mortal. Analogical reasoning is a weaker form of inductive reasoning from a single example, because inductive reasoning typically uses a large number of examples to reason from the particular to the general. Analogical reasoning often leads to wrong conclusions. For example: * Premise 1: Socrates is human and male. * Premise 2:
Ada Lovelace Augusta Ada King, Countess of Lovelace (''née'' Byron; 10 December 1815 – 27 November 1852) was an English mathematician and writer, chiefly known for her work on Charles Babbage's proposed mechanical general-purpose computer, the A ...
is human. * Conclusion: Ada Lovelace is male.


Abductive reasoning

Abductive reasoning, or argument to the best explanation, is a form of reasoning that doesn't fit in deductive or inductive, since it starts with incomplete set of observations and proceeds with likely possible explanations so the conclusion in an abductive argument does not follow with certainty from its premises and concerns something unobserved. What distinguishes abduction from the other forms of reasoning is an attempt to favour one conclusion above others, by subjective judgement or attempting to falsify alternative explanations or by demonstrating the likelihood of the favoured conclusion, given a set of more or less disputable assumptions. For example, when a patient displays certain symptoms, there might be various possible causes, but one of these is preferred above others as being more probable.


Fallacious reasoning

Flawed reasoning in arguments is known as fallacious reasoning. Bad reasoning within arguments can be because it commits either a
formal fallacy In philosophy, a formal fallacy, deductive fallacy, logical fallacy or non sequitur (; Latin for " tdoes not follow") is a pattern of reasoning rendered invalid by a flaw in its logical structure that can neatly be expressed in a standard logic syst ...
or an
informal fallacy Informal fallacies are a type of incorrect argument in natural language. The source of the error is not just due to the ''form'' of the argument, as is the case for formal fallacies, but can also be due to their ''content'' and ''context''. Fall ...
. Formal fallacies occur when there is a problem with the form, or structure, of the argument. The word "formal" refers to this link to the ''form'' of the argument. An argument that contains a formal fallacy will always be invalid. An informal fallacy is an error in reasoning that occurs due to a problem with the ''content'', rather than mere ''structure'', of the argument.


Traditional problems raised concerning reason

Philosophy is sometimes described as a life of reason, with normal human reason pursued in a more consistent and dedicated way than usual. Two categories of problem concerning reason have long been discussed by philosophers concerning reason, essentially being reasonings about reasoning itself as a human aim, or philosophizing about philosophizing. The first question is concerning whether we can be confident that reason can achieve
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 ...
of
truth Truth is the property of being in accord with fact or reality.Merriam-Webster's Online Dictionarytruth 2005 In everyday language, truth is typically ascribed to things that aim to represent reality or otherwise correspond to it, such as beliefs ...
better than other ways of trying to achieve such knowledge. The other question is whether a life of reason, a life that aims to be guided by reason, can be expected to achieve a happy life more so than other ways of life (whether such a life of reason results in knowledge or not).


Reason versus truth, and "first principles"

Since classical times a question has remained constant in philosophical debate (which is sometimes seen as a conflict between movements called
Platonism Platonism is the philosophy of Plato and philosophical systems closely derived from it, though contemporary platonists do not necessarily accept all of the doctrines of Plato. Platonism had a profound effect on Western thought. Platonism at le ...
and
Aristotelianism Aristotelianism ( ) is a philosophical tradition inspired by the work of Aristotle, usually characterized by deductive logic and an analytic inductive method in the study of natural philosophy and metaphysics. It covers the treatment of the socia ...
) concerning the role of reason in confirming
truth Truth is the property of being in accord with fact or reality.Merriam-Webster's Online Dictionarytruth 2005 In everyday language, truth is typically ascribed to things that aim to represent reality or otherwise correspond to it, such as beliefs ...
. People use logic, deduction, and
induction Induction, Inducible or Inductive may refer to: Biology and medicine * Labor induction (birth/pregnancy) * Induction chemotherapy, in medicine * Induced stem cells, stem cells derived from somatic, reproductive, pluripotent or other cell t ...
, to reach conclusions they think are true. Conclusions reached in this way are considered, according to Aristotle, more certain than sense perceptions on their own. On the other hand, if such reasoned conclusions are only built originally upon a foundation of sense perceptions, then, our most logical conclusions can never be said to be certain because they are built upon the very same fallible perceptions they seek to better. This leads to the question of what types of
first principles In philosophy and science, a first principle is a basic proposition or assumption that cannot be deduced from any other proposition or assumption. First principles in philosophy are from First Cause attitudes and taught by Aristotelians, and nua ...
, or starting points of reasoning, are available for someone seeking to come to true conclusions. In Greek, "
first principles In philosophy and science, a first principle is a basic proposition or assumption that cannot be deduced from any other proposition or assumption. First principles in philosophy are from First Cause attitudes and taught by Aristotelians, and nua ...
" are '' archai'', "starting points", and the faculty used to perceive them is sometimes referred to in Aristotle and Plato as '' nous'' which was close in meaning to ''awareness'' or ''
consciousness Consciousness, at its simplest, is sentience and awareness of internal and external existence. However, the lack of definitions has led to millennia of analyses, explanations and debates by philosophers, theologians, linguisticians, and scien ...
''. Empiricism (sometimes associated with Aristotle but more correctly associated with
British British may refer to: Peoples, culture, and language * British people, nationals or natives of the United Kingdom, British Overseas Territories, and Crown Dependencies. ** Britishness, the British identity and common culture * British English, ...
philosophers such as
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 Enlightenment, Enlightenment thinkers and commonly known as the "father of liberalism ...
and
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 999br>David Hume" ''Encyclopædia Britannica''. Retrieved 18 May 2020. was a Scottish Enlightenment phil ...
, as well as their ancient equivalents such as
Democritus Democritus (; el, Δημόκριτος, ''Dēmókritos'', meaning "chosen of the people"; – ) was an Ancient Greek pre-Socratic philosopher from Abdera, primarily remembered today for his formulation of an atomic theory of the universe. No ...
) asserts that sensory impressions are the only available starting points for reasoning and attempting to attain truth. This approach always leads to the controversial conclusion that
absolute knowledge In philosophy, universality or absolutism is the idea that universal facts exist and can be progressively discovered, as opposed to relativism, which asserts that all facts are merely relative to one's perspective. Absolutism and relativism have ...
is not attainable.
Idealism In philosophy, the term idealism identifies and describes metaphysical perspectives which assert that reality is indistinguishable and inseparable from perception and understanding; that reality is a mental construct closely connected t ...
, (associated with Plato and his school), claims that there is a "higher" reality, from which certain people can directly arrive at truth without needing to rely only upon the senses, and that this higher reality is therefore the primary source of truth. Philosophers such as
Plato Plato ( ; grc-gre, Πλάτων ; 428/427 or 424/423 – 348/347 BC) was a Greek philosopher born in Athens during the Classical period in Ancient Greece. He founded the Platonist school of thought and the Academy, the first institution ...
,
Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of phil ...
,
Al-Farabi Abu Nasr Muhammad Al-Farabi ( fa, ابونصر محمد فارابی), ( ar, أبو نصر محمد الفارابي), known in the West as Alpharabius; (c. 872 – between 14 December, 950 and 12 January, 951)PDF version was a renowned early Isl ...
, Avicenna,
Averroes Ibn Rushd ( ar, ; full name in ; 14 April 112611 December 1198), often Latinized as Averroes ( ), was an Andalusian polymath and jurist who wrote about many subjects, including philosophy, theology, medicine, astronomy, physics, psy ...
,
Maimonides Musa ibn Maimon (1138–1204), commonly known as Maimonides (); la, Moses Maimonides and also referred to by the acronym Rambam ( he, רמב״ם), was a Sephardic Jewish philosopher who became one of the most prolific and influential Torah ...
,
Aquinas Thomas Aquinas, OP (; it, Tommaso d'Aquino, lit=Thomas of Aquino; 1225 – 7 March 1274) was an Italian Dominican friar and priest who was an influential philosopher, theologian and jurist in the tradition of scholasticism; he is known ...
and Hegel are sometimes said to have argued that reason must be fixed and discoverable—perhaps by dialectic, analysis, or study. In the vision of these thinkers, reason is divine or at least has divine attributes. Such an approach allowed religious philosophers such as
Thomas Aquinas Thomas Aquinas, OP (; it, Tommaso d'Aquino, lit=Thomas of Aquino; 1225 – 7 March 1274) was an Italian Dominican friar and priest who was an influential philosopher, theologian and jurist in the tradition of scholasticism; he is known wi ...
and
Étienne Gilson Étienne Henri Gilson (; 13 June 1884 – 19 September 1978) was a French philosopher and historian of philosophy. A scholar of medieval philosophy, he originally specialised in the thought of Descartes; he also philosophized in the tradition ...
to try to show that reason and
revelation In religion and theology, revelation is the revealing or disclosing of some form of truth or knowledge through communication with a deity or other supernatural entity or entities. Background Inspiration – such as that bestowed by God on the ...
are compatible. According to Hegel, "...the only thought which Philosophy brings with it to the contemplation of
History History (derived ) is the systematic study and the documentation of the human activity. The time period of event before the History of writing#Inventions of writing, invention of writing systems is considered prehistory. "History" is an umbr ...
, is the simple conception of reason; that reason is the Sovereign of the World; that the history of the world, therefore, presents us with a rational process." Since the 17th century rationalists, reason has often been taken to be a subjective faculty, or rather the unaided ability (
pure reason Speculative reason, sometimes called theoretical reason or pure reason, is theoretical (or logical, deductive) thought, as opposed to practical (active, willing) thought. The distinction between the two goes at least as far back as the ancient Gr ...
) to form concepts. For Descartes,
Spinoza Baruch (de) Spinoza (born Bento de 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 Portuguese-Jewish origin, ...
and
Leibniz Gottfried Wilhelm (von) Leibniz . ( – 14 November 1716) was a German polymath active as a mathematician, philosopher, scientist and diplomat. He is one of the most prominent figures in both the history of philosophy and the history of ma ...
, this was associated with
mathematics 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 ...
.
Kant Immanuel Kant (, , ; 22 April 1724 – 12 February 1804) was a German philosopher and one of the central Enlightenment thinkers. Born in Königsberg, Kant's comprehensive and systematic works in epistemology, metaphysics, ethics, and aest ...
attempted to show that pure reason could form concepts (
time Time is the continued sequence of existence and events that occurs in an apparently irreversible succession from the past, through the present, into the future. It is a component quantity of various measurements used to sequence events, to ...
and
space Space is the boundless three-dimensional extent in which objects and events have relative position and direction. In classical physics, physical space is often conceived in three linear dimensions, although modern physicists usually cons ...
) that are the conditions of experience. Kant made his argument in opposition to Hume, who denied that reason had any role to play in experience.


Reason versus emotion or passion

After Plato and Aristotle,
western literature Western literature, also known as European literature, is the literature written in the context of Western culture in the languages of Europe, as well as several geographically or historically related languages such as Basque and Hungarian, an ...
often treated reason as being the faculty that trained the passions and appetites.
Stoic philosophy Stoicism is a school of Hellenistic philosophy founded by Zeno of Citium in Athens in the early 3rd century BCE. It is a philosophy of personal virtue ethics informed by its system of logic and its views on the natural world, asserting that t ...
, by contrast, claimed most emotions were merely false judgements. According to the stoics the only good is virtue, and the only evil is vice, therefore emotions that judged things other than vice to be bad (such as fear or distress), or things other than virtue to be good (such as greed) were simply false judgements and should be discarded (though positive emotions based on true judgements, such as kindness, were acceptable). After the critiques of reason in the early Enlightenment the appetites were rarely discussed or conflated with the passions. Some Enlightenment camps took after the Stoics to say Reason should oppose Passion rather than order it, while others like the Romantics believed that Passion displaces Reason, as in the maxim "follow your heart". Reason has been seen as cold, an "enemy of mystery and ambiguity", a slave, or judge, of the passions, notably in the work of
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 999br>David Hume" ''Encyclopædia Britannica''. Retrieved 18 May 2020. was a Scottish Enlightenment phil ...
, and more recently of Freud. Reasoning which claims that the object of a desire is demanded by logic alone is called '' rationalization''.
Rousseau Jean-Jacques Rousseau (, ; 28 June 1712 – 2 July 1778) was a Genevan philosopher, writer, and composer. His political philosophy influenced the progress of the Age of Enlightenment throughout Europe, as well as aspects of the French Revolu ...
first proposed, in his second '' Discourse'', that reason and political life is not natural and possibly harmful to mankind. He asked what really can be said about what is natural to mankind. What, other than reason and civil society, "best suits his constitution"? Rousseau saw "two principles prior to reason" in human nature. First we hold an intense interest in our own well-being. Secondly we object to the suffering or death of any sentient being, especially one like ourselves. These two passions lead us to desire more than we could achieve. We become dependent upon each other, and on relationships of authority and obedience. This effectively puts the human race into slavery. Rousseau says that he almost dares to assert that nature does not destine men to be healthy. According to
Richard Velkley Richard L. Velkley (born March 17, 1949) is an American philosopher and Celia Scott Weatherhead Distinguished Professor of Philosophy at Tulane University. Velkley is known for his expertise on Kant, Rousseau, and post-Kantian philosophy. He is a ...
, "Rousseau outlines certain programs of rational self-correction, most notably the political legislation of the '' Contrat Social'' and the moral education in '' Émile''. All the same, Rousseau understands such corrections to be only ameliorations of an essentially unsatisfactory condition, that of socially and intellectually corrupted humanity." This quandary presented by Rousseau led to
Kant Immanuel Kant (, , ; 22 April 1724 – 12 February 1804) was a German philosopher and one of the central Enlightenment thinkers. Born in Königsberg, Kant's comprehensive and systematic works in epistemology, metaphysics, ethics, and aest ...
's new way of justifying reason as freedom to create good and evil. These therefore are not to be blamed on nature or God. In various ways,
German Idealism German idealism was a philosophical movement that emerged in Germany in the late 18th and early 19th centuries. It developed out of the work of Immanuel Kant in the 1780s and 1790s, and was closely linked both with Romanticism and the revolutionary ...
after Kant, and major later figures such
Nietzsche Friedrich Wilhelm Nietzsche (; or ; 15 October 1844 – 25 August 1900) was a German philosopher, prose poet, cultural critic, philologist, and composer whose work has exerted a profound influence on contemporary philosophy. He began his car ...
,
Bergson Henri-Louis Bergson (; 18 October 1859 – 4 January 1941) was a French philosopherHenri Bergson. 2014. Encyclopædia Britannica Online. Retrieved 13 August 2014, from https://www.britannica.com/EBchecked/topic/61856/Henri-Bergson
,
Husserl , thesis1_title = Beiträge zur Variationsrechnung (Contributions to the Calculus of Variations) , thesis1_url = https://fedora.phaidra.univie.ac.at/fedora/get/o:58535/bdef:Book/view , thesis1_year = 1883 , thesis2_title ...
, Scheler, and
Heidegger Martin Heidegger (; ; 26 September 188926 May 1976) was a German philosopher who is best known for contributions to phenomenology, hermeneutics, and existentialism. He is among the most important and influential philosophers of the 20th centur ...
, remain preoccupied with problems coming from the metaphysical demands or ''urges'' of ''reason''. The influence of Rousseau and these later writers is also large upon art and politics. Many writers (such as
Nikos Kazantzakis Nikos Kazantzakis ( el, ; 2 March (Old Style and New Style dates, OS 18 February) 188326 October 1957) was a Greeks, Greek writer. Widely considered a giant of modern Greek literature, he was nominated for the Nobel Prize in Literature in ni ...
) extol passion and disparage reason. In politics modern
nationalism Nationalism is an idea and movement that holds that the nation should be congruent with the State (polity), state. As a movement, nationalism tends to promote the interests of a particular nation (as in a in-group and out-group, group of peo ...
comes from Rousseau's argument that rationalist cosmopolitanism brings man ever further from his natural state. Another view on reason and emotion was proposed in the 1994 book titled '' Descartes' Error'' by
Antonio Damasio Antonio Damasio ( pt, António Damásio) is a Portuguese-American neuroscientist. He is currently the David Dornsife Chair in Neuroscience, as well as Professor of Psychology, Philosophy, and Neurology, at the University of Southern California, ...
. In it, Damasio presents the "
Somatic Marker Hypothesis The somatic marker hypothesis, formulated by Antonio Damasio and associated researchers, proposes that emotional processes guide (or bias) behavior, particularly decision-making. ''Descartes' Error'' "Somatic markers" are feelings in the body th ...
" which states that emotions guide behavior and decision-making. Damasio argues that these somatic markers (known collectively as "gut feelings") are "intuitive signals" that direct our decision making processes in a certain way that cannot be solved with rationality alone. Damasio further argues that rationality requires emotional input in order to function.


Reason versus faith or tradition

There are many religious traditions, some of which are explicitly fideist and others of which claim varying degrees of
rationalism In philosophy, rationalism is the epistemological view that "regards reason as the chief source and test of knowledge" or "any view appealing to reason as a source of knowledge or justification".Lacey, A.R. (1996), ''A Dictionary of Philosophy ...
. Secular critics sometimes accuse all religious adherents of irrationality, since they claim such adherents are guilty of ignoring, suppressing, or forbidding some kinds of reasoning concerning some subjects (such as religious dogmas, moral taboos, etc.). Though the theologies and
religion Religion is usually defined as a social- cultural system of designated behaviors and practices, morals, beliefs, worldviews, texts, sanctified places, prophecies, ethics, or organizations, that generally relates humanity to supernatural, ...
s such as classical monotheism typically do not admit to be
irrational Irrationality is cognition, thinking, talking, or acting without inclusion of rationality. It is more specifically described as an action or opinion given through inadequate use of reason, or through emotional distress or cognitive deficiency. T ...
, there is often a perceived conflict or tension between
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 ofte ...
and
tradition A tradition is a belief or behavior (folk custom) passed down within a group or society with symbolic meaning or special significance with origins in the past. A component of cultural expressions and folklore, common examples include holidays or ...
on the one hand, and reason on the other, as potentially competing sources of
wisdom Wisdom, sapience, or sagacity is the ability to contemplate and act using knowledge, experience, understanding, common sense and insight. Wisdom is associated with attributes such as unbiased judgment, compassion, experiential self-knowle ...
,
law Law is a set of rules that are created and are enforceable by social or governmental institutions to regulate behavior,Robertson, ''Crimes against humanity'', 90. with its precise definition a matter of longstanding debate. It has been vario ...
and
truth Truth is the property of being in accord with fact or reality.Merriam-Webster's Online Dictionarytruth 2005 In everyday language, truth is typically ascribed to things that aim to represent reality or otherwise correspond to it, such as beliefs ...
. Religious adherents sometimes respond by arguing that faith and reason can be reconciled, or have different non-overlapping domains, or that critics engage in a similar kind of irrationalism: * ''Reconciliation'': Philosopher
Alvin Plantinga Alvin Carl Plantinga (born November 15, 1932) is an American analytic philosopher who works primarily in the fields of philosophy of religion, epistemology (particularly on issues involving epistemic justification), and logic. From 1963 to 198 ...
argues that there is no real conflict between reason and classical theism because classical theism explains (among other things) why the universe is intelligible and why reason can successfully grasp it. * ''Non-overlapping magisteria'': Evolutionary biologist Stephen Jay Gould argues that there need not be conflict between reason and religious belief because they are each authoritative in their own domain (or "magisterium"). If so, reason can work on those problems over which it has authority while other sources of knowledge or opinion can have authority on the big questions. * ''
Tu quoque (; Latin , for "you also") is a discussion technique that intends to discredit the opponent's argument by attacking the opponent's own personal behavior and actions as being inconsistent with their argument, therefore accusing hypocrisy. This ...
'': Philosophers Alasdair MacIntyre and Charles Taylor argue that those critics of traditional religion who are adherents of
secular Secularity, also the secular or secularness (from Latin ''saeculum'', "worldly" or "of a generation"), is the state of being unrelated or neutral in regards to religion. Anything that does not have an explicit reference to religion, either negativ ...
liberalism Liberalism is a political and moral philosophy based on the rights of the individual, liberty, consent of the governed, political equality and equality before the law."political rationalism, hostility to autocracy, cultural distaste for c ...
are also sometimes guilty of ignoring, suppressing, and forbidding some kinds of reasoning about subjects. Similarly, philosophers of science such as Paul Feyarabend argue that scientists sometimes ignore or suppress evidence contrary to the dominant paradigm. * ''Unification'': Theologian Joseph Ratzinger, later
Benedict XVI Pope Benedict XVI ( la, Benedictus XVI; it, Benedetto XVI; german: link=no, Benedikt XVI.; born Joseph Aloisius Ratzinger, , on 16 April 1927) is a retired prelate of the Catholic church who served as the head of the Church and the sovereign ...
, asserted that "Christianity has understood itself as the religion of the Logos, as the religion according to reason," referring to John 1:Ἐν ἀρχῇ ἦν ὁ λόγος, usually translated as "In the beginning was the Word (Logos)." Thus, he said that the Christian faith is "open to all that is truly rational", and that the rationality of Western Enlightenment "is of Christian origin". Some commentators have claimed that
Western civilization Leonardo da Vinci's ''Vitruvian Man''. Based on the correlations of ideal Body proportions">human proportions with geometry described by the ancient Roman architect Vitruvius in Book III of his treatise ''De architectura''. image:Plato Pio-Cle ...
can be almost defined by its serious testing of the limits of tension between "unaided" reason and
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 ofte ...
in "
revealed Reveal or Revealed may refer to: People * Reveal (rapper) (born 1983), member of the British hip hop group Poisonous Poets * James L. Reveal (1941–2015), American botanist Arts, entertainment, and media Literature * ''Revealed'', a 2013 novel ...
" truths—figuratively summarized as
Athens Athens ( ; el, Αθήνα, Athína ; grc, Ἀθῆναι, Athênai (pl.) ) is both the capital and largest city of Greece. With a population close to four million, it is also the seventh largest city in the European Union. Athens dominates ...
and
Jerusalem Jerusalem (; he, יְרוּשָׁלַיִם ; ar, القُدس ) (combining the Biblical and common usage Arabic names); grc, Ἱερουσαλήμ/Ἰεροσόλυμα, Hierousalḗm/Hierosóluma; hy, Երուսաղեմ, Erusałēm. i ...
, respectively. Leo Strauss spoke of a "Greater
West West or Occident is one of the four cardinal directions or points of the compass. It is the opposite direction from east and is the direction in which the Sunset, Sun sets on the Earth. Etymology The word "west" is a Germanic languages, German ...
" that included all areas under the influence of the tension between Greek rationalism and
Abrahamic The Abrahamic religions are a group of religions centered around worship of the God of Abraham. Abraham, a Hebrew patriarch, is extensively mentioned throughout Abrahamic religious scriptures such as the Bible and the Quran. Jewish tradition ...
revelation, including the
Muslim Muslims ( ar, المسلمون, , ) are people who adhere to Islam, a monotheistic religion belonging to the Abrahamic tradition. They consider the Quran, the foundational religious text of Islam, to be the verbatim word of the God of Abrah ...
lands. He was particularly influenced by the great Muslim philosopher
Al-Farabi Abu Nasr Muhammad Al-Farabi ( fa, ابونصر محمد فارابی), ( ar, أبو نصر محمد الفارابي), known in the West as Alpharabius; (c. 872 – between 14 December, 950 and 12 January, 951)PDF version was a renowned early Isl ...
. To consider to what extent Eastern philosophy might have partaken of these important tensions, Strauss thought it best to consider whether dharma or
tao ''Tao'' or ''Dao'' is the natural order of the universe, whose character one's intuition must discern to realize the potential for individual wisdom, as conceived in the context of East Asian philosophy, East Asian religions, or any other phil ...
may be equivalent to
Nature Nature, in the broadest sense, is the physics, physical world or universe. "Nature" can refer to the phenomenon, phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. ...
(by which we mean ''
physis Fusis, Phusis or Physis (; grc, φύσις ) is a Greek philosophical, theological, and scientific term, usually translated into English—according to its Latin translation "natura"—as "nature". The term originated in ancient Greek philosophy ...
'' in Greek). According to Strauss the beginning of philosophy involved the "discovery or invention of nature" and the "pre-philosophical equivalent of nature" was supplied by "such notions as 'custom' or 'ways, which appear to be ''really universal in all times and places''. The philosophical concept of nature or natures as a way of understanding ''archai'' (first principles of knowledge) brought about a peculiar tension between reasoning on the one hand, and tradition or faith on the other. Although there is this special history of debate concerning reason and faith in the Islamic, Christian and Jewish traditions, the pursuit of reason is sometimes argued to be compatible with the other practice of other religions of a different nature, such as
Hinduism Hinduism () is an Indian religion or '' dharma'', a religious and universal order or way of life by which followers abide. As a religion, it is the world's third-largest, with over 1.2–1.35 billion followers, or 15–16% of the global p ...
, because they do not define their tenets in such an absolute way.


Reason in particular fields of study


Psychology and cognitive science

Scientific research into reasoning is carried out within the fields of
psychology Psychology is the scientific study of mind and behavior. Psychology includes the study of conscious and unconscious phenomena, including feelings and thoughts. It is an academic discipline of immense scope, crossing the boundaries betwe ...
and cognitive science. Psychologists attempt to determine whether or not people are capable of rational thought in a number of different circumstances. Assessing how well someone engages in reasoning is the project of determining the extent to which the person is
rational Rationality is the quality of being guided by or based on reasons. In this regard, a person acts rationally if they have a good reason for what they do or a belief is rational if it is based on strong evidence. This quality can apply to an abi ...
or acts rationally. It is a key research question in the
psychology of reasoning The psychology of reasoning (also known as the cognitive science of reasoning) is the study of how people reason, often broadly defined as the process of drawing conclusions to inform how people solve problems and make decisions. It overlaps w ...
and cognitive science of reasoning.
Rationality Rationality is the quality of being guided by or based on reasons. In this regard, a person acts rationally if they have a good reason for what they do or a belief is rational if it is based on strong evidence. This quality can apply to an abil ...
is often divided into its respective theoretical and practical counterparts.


Behavioral experiments on human reasoning

Experimental cognitive psychologists carry out research on reasoning behaviour. Such research may focus, for example, on how people perform on tests of reasoning such as
intelligence Intelligence has been defined in many ways: the capacity for abstraction, logic, understanding, self-awareness, learning, emotional knowledge, reasoning, planning, creativity, critical thinking, and problem-solving. More generally, it can b ...
or IQ tests, or on how well people's reasoning matches ideals set by logic (see, for example, the Wason test). Experiments examine how people make inferences from conditionals e.g., ''If A then B'' and how they make inferences about alternatives, e.g., ''A or else B''. They test whether people can make valid deductions about spatial and temporal relations, e.g., ''A is to the left of B'', or ''A happens after B'', and about quantified assertions, e.g., ''All the A are B''. Experiments investigate how people make inferences about factual situations, hypothetical possibilities, probabilities, and
counterfactual Counterfactual conditionals (also ''subjunctive'' or ''X-marked'') are conditional sentences which discuss what would have been true under different circumstances, e.g. "If Peter believed in ghosts, he would be afraid to be here." Counterfactual ...
situations.


Developmental studies of children's reasoning

Developmental psychologists investigate the development of reasoning from birth to adulthood. Piaget's
theory of cognitive development Piaget's theory of cognitive development is a comprehensive theory about the nature and development of human intelligence. It was originated by the Swiss developmental psychologist Jean Piaget (1896–1980). The theory deals with the nature of k ...
was the first complete theory of reasoning development. Subsequently, several alternative theories were proposed, including the neo-Piagetian theories of cognitive development.


Neuroscience of reasoning

The biological functioning of the brain is studied by neurophysiologists, cognitive neuroscientists and
neuropsychologist Neuropsychology is a branch of psychology concerned with how a person's cognition and behavior are related to the brain and the rest of the nervous system. Professionals in this branch of psychology often focus on how injuries or illnesses of t ...
s. Research in this area includes research into the structure and function of normally functioning brains, and of damaged or otherwise unusual brains. In addition to carrying out research into reasoning, some psychologists, for example, clinical psychologists and
psychotherapists Psychotherapy (also psychological therapy, talk therapy, or talking therapy) is the use of psychological methods, particularly when based on regular personal interaction, to help a person change behavior, increase happiness, and overcome prob ...
work to alter people's reasoning habits when they are unhelpful.


Computer science


Automated reasoning

In
artificial intelligence Artificial intelligence (AI) is intelligence—perceiving, synthesizing, and inferring information—demonstrated by machines, as opposed to intelligence displayed by animals and humans. Example tasks in which this is done include speech r ...
and
computer science Computer science is the study of computation, automation, and information. Computer science spans theoretical disciplines (such as algorithms, theory of computation, information theory, and automation) to Applied science, practical discipli ...
, scientists study and use
automated reasoning In computer science, in particular in knowledge representation and reasoning and metalogic, the area of automated reasoning is dedicated to understanding different aspects of reasoning. The study of automated reasoning helps produce computer prog ...
for diverse applications including
automated theorem proving Automated theorem proving (also known as ATP or automated deduction) is a subfield of automated reasoning and mathematical logic dealing with proving mathematical theorems by computer programs. Automated reasoning over mathematical proof was a ma ...
the
formal semantics of programming languages In programming language theory, semantics is the rigorous mathematical study of the meaning of programming languages. Semantics assigns computational meaning to valid strings in a programming language syntax. Semantics describes the processes ...
, and
formal specification In computer science, formal specifications are mathematically based techniques whose purpose are to help with the implementation of systems and software. They are used to describe a system, to analyze its behavior, and to aid in its design by verif ...
in
software engineering Software engineering is a systematic engineering approach to software development. A software engineer is a person who applies the principles of software engineering to design, develop, maintain, test, and evaluate computer software. The term '' ...
.


Meta-reasoning

Meta-reasoning is reasoning about reasoning. In computer science, a system performs meta-reasoning when it is reasoning about its own operation. This requires a programming language capable of
reflection Reflection or reflexion may refer to: Science and technology * Reflection (physics), a common wave phenomenon ** Specular reflection, reflection from a smooth surface *** Mirror image, a reflection in a mirror or in water ** Signal reflection, in ...
, the ability to observe and modify its own structure and behaviour.


Evolution of reason

A species could benefit greatly from better abilities to reason about, predict and understand the world. French social and cognitive scientists
Dan Sperber Dan Sperber (born 20 June 1942 in Cagnes-sur-Mer) is a French social and cognitive scientist and philosopher. His most influential work has been in the fields of cognitive anthropology, linguistic pragmatics, psychology of reasoning, and phil ...
and Hugo Mercier argue that there could have been other forces driving the evolution of reason. They point out that reasoning is very difficult for humans to do effectively, and that it is hard for individuals to doubt their own beliefs (confirmation bias). Reasoning is most effective when it is done as a collective – as demonstrated by the success of projects like
science Science is a systematic endeavor that builds and organizes knowledge in the form of testable explanations and predictions about the universe. Science may be as old as the human species, and some of the earliest archeological evidence for ...
. They suggest that there are not just individual, but group selection pressures at play. Any group that managed to find ways of reasoning effectively would reap benefits for all its members, increasing their fitness (biology), fitness. This could also help explain why humans, according to Sperber, are not optimized to reason effectively alone. Their argumentative theory of reasoning claims that reason may have more to do with winning arguments than with the search for the truth.


Reason in political philosophy and ethics

Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of phil ...
famously described reason (with language) as a part of
human nature Human nature is a concept that denotes the fundamental dispositions and characteristics—including ways of thinking, feeling, and acting—that humans are said to have naturally. The term is often used to denote the essence of humankind, or ...
, which means that it is best for humans to live "politically" meaning in communities of about the size and type of a small city state (''polis'' in Greek). For example...
It is clear, then, that a human being is more of a political [''politikon'' = of the ''polis''] animal [''zōion''] than is any bee or than any of those animals that live in herds. For nature, as we say, makes nothing in vain, and humans are the only animals who possess reasoned speech [''logos'']. Voice, of course, serves to indicate what is painful and pleasant; that is why it is also found in other animals, because their nature has reached the point where they can perceive what is painful and pleasant and express these to each other. But speech [''logos''] serves to make plain what is advantageous and harmful and so also what is just and unjust. For it is a peculiarity of humans, in contrast to the other animals, to have perception of good and bad, just and unjust, and the like; and the community in these things makes a household or city [''polis'']. ..By nature, then, the drive for such a community exists in everyone, but the first to set one up is responsible for things of very great goodness. For as humans are the best of all animals when perfected, so they are the worst when divorced from law and right. The reason is that injustice is most difficult to deal with when furnished with weapons, and the weapons a human being has are meant by nature to go along with prudence and virtue, but it is only too possible to turn them to contrary uses. Consequently, if a human being lacks virtue, he is the most unholy and savage thing, and when it comes to sex and food, the worst. But justice is something political [to do with the ''polis''], for right is the arrangement of the political community, and right is discrimination of what is just. (Aristotle's Politics 1253a 1.2. Peter Simpson's translation, with Greek terms inserted in square brackets.)
The concept of human nature being fixed in this way, implied, in other words, that we can define what type of community is always best for people. This argument has remained a central argument in all political, ethical and moral thinking since then, and has become especially controversial since firstly
Rousseau Jean-Jacques Rousseau (, ; 28 June 1712 – 2 July 1778) was a Genevan philosopher, writer, and composer. His political philosophy influenced the progress of the Age of Enlightenment throughout Europe, as well as aspects of the French Revolu ...
's Second Discourse, and secondly, the Theory of Evolution. Already in Aristotle there was an awareness that the ''polis'' had not always existed and had needed to be invented or developed by humans themselves. The household came first, and the first villages and cities were just extensions of that, with the first cities being run as if they were still families with Kings acting like fathers.Politics I.2.1252b15
Friendship [''philia''] seems to prevail [in] man and woman according to
nature Nature, in the broadest sense, is the physics, physical world or universe. "Nature" can refer to the phenomenon, phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. ...
[''kata phusin'']; for people are by nature [''tēi phusei''] pairing [''sunduastikon''] more than political [''politikon'' = of the ''polis''], in as much as the household [''oikos''] is prior [''proteron'' = earlier] and more necessary than the ''polis'' and making children is more common [''koinoteron''] with the animals. In the other animals, community [''koinōnia''] goes no further than this, but people live together [''sumoikousin''] not only for the sake of making children, but also for the things for life; for from the start the functions [''erga''] are divided, and are different [for] man and woman. Thus they supply each other, putting their own into the common [''eis to koinon'']. It is for these [reasons] that both utility [''chrēsimon''] and pleasure [''hēdu''] seem to be found in this kind of friendship. (Nicomachean Ethics, VIII.12.1162a. Rough literal translation with Greek terms shown in square brackets.)
Rousseau Jean-Jacques Rousseau (, ; 28 June 1712 – 2 July 1778) was a Genevan philosopher, writer, and composer. His political philosophy influenced the progress of the Age of Enlightenment throughout Europe, as well as aspects of the French Revolu ...
in his Second Discourse finally took the shocking step of claiming that this traditional account has things in reverse: with reason, language and rationally organized communities all having developed over a long period of time merely as a result of the fact that some habits of cooperation were found to solve certain types of problems, and that once such cooperation became more important, it forced people to develop increasingly complex cooperation—often only to defend themselves from each other. In other words, according to Rousseau, reason, language and rational community did not arise because of any conscious decision or plan by humans or gods, nor because of any pre-existing human nature. As a result, he claimed, living together in rationally organized communities like modern humans is a development with many negative aspects compared to the original state of man as an ape. If anything is specifically human in this theory, it is the flexibility and adaptability of humans. This view of the animal origins of distinctive human characteristics later received support from Charles Darwin's Theory of Evolution. The two competing theories concerning the origins of reason are relevant to political and ethical thought because, according to the Aristotelian theory, a best way of living together exists independently of historical circumstances. According to Rousseau, we should even doubt that reason, language and politics are a good thing, as opposed to being simply the best option given the particular course of events that lead to today. Rousseau's theory, that human nature is malleable rather than fixed, is often taken to imply, for example by Karl Marx, a wider range of possible ways of living together than traditionally known. However, while Rousseau's initial impact encouraged bloody revolutions against traditional politics, including both the French Revolution and the Russian Revolution (1917), Russian Revolution, his own conclusions about the best forms of community seem to have been remarkably classical, in favor of city-states such as Geneva, and Arcadia (utopia), rural living.


See also

* Argument * Argumentation theory * Confirmation bias * Conformity * Critical thinking * Logic and rationality * Outline of thought – topic tree that identifies many types of thoughts/thinking, types of reasoning, aspects of thought, related fields, and more. * Outline of human intelligence – topic tree presenting the traits, capacities, models, and research fields of human intelligence, and more. * Common sense


References


Further reading

* * Beer, Francis A., "Words of Reason", ''Political Communication'' 11 (Summer, 1994): 185–201. * {{Authority control Reasoning, Age of Enlightenment Cognition Concepts in epistemology Concepts in ethics Concepts in logic Concepts in metaphilosophy Concepts in the philosophy of mind Concepts in the philosophy of science Critical thinking Idealism Knowledge Metaphysics of mind Ontology Philosophical logic Philosophy of logic Problem solving skills Rationalism Truth Virtue