A priori and a posteriori (philosophy)

A priori and a posteriori (philosophy)

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The terms a priori and a posteriori ("from the later") are used in philosophy
Philosophy is the study of general and fundamental problems, such as those connected with existence, knowledge, values, reason, mind, and language. Philosophy is distinguished from other ways of addressing such problems by its critical, generally systematic approach and its reliance on rational...

 (epistemology) to distinguish two types of knowledge
Knowledge is a familiarity with someone or something unknown, which can include information, facts, descriptions, or skills acquired through experience or education. It can refer to the theoretical or practical understanding of a subject...

, justifications or argument
In philosophy and logic, an argument is an attempt to persuade someone of something, or give evidence or reasons for accepting a particular conclusion.Argument may also refer to:-Mathematics and computer science:...

s. A priori knowledge or justification is independent of experience
Experience as a general concept comprises knowledge of or skill in or observation of some thing or some event gained through involvement in or exposure to that thing or event....

 (for example 'All bachelors are unmarried'); a posteriori knowledge or justification is dependent on experience
Experience as a general concept comprises knowledge of or skill in or observation of some thing or some event gained through involvement in or exposure to that thing or event....

 or empirical
The word empirical denotes information gained by means of observation or experimentation. Empirical data are data produced by an experiment or observation....

Evidence in its broadest sense includes everything that is used to determine or demonstrate the truth of an assertion. Giving or procuring evidence is the process of using those things that are either presumed to be true, or were themselves proven via evidence, to demonstrate an assertion's truth...

 (for example 'Some bachelors are very happy'). A posteriori justification makes reference to experience; but the issue concerns how one knows the proposition or claim in question—what justifies or grounds one's belief in it. Galen Strawson
Galen Strawson
Galen John Strawson is a British philosopher and literary critic who works primarily on philosophy of mind, metaphysics , John Locke, David Hume and Kant. He was educated at the Dragon School, Oxford , from where he won a scholarship to Winchester College...

 wrote that an a priori argument is one in which "you can see that it is true
True may refer to:* Truth, the state of being in accord with fact or reality-Music:* True , 1996* True , 2002* True , 1983** "True"...

 just lying on your couch. You don't have to get up off your couch and go outside and examine the way things are in the physical world. You don't have to do any science." There are many points of view on these two types of assertions, and their relationship is one of the oldest problems in modern philosophy.

See also the related distinctions: deductive
Deductive reasoning
Deductive reasoning, also called deductive logic, is reasoning which constructs or evaluates deductive arguments. Deductive arguments are attempts to show that a conclusion necessarily follows from a set of premises or hypothesis...

Inductive reasoning
Inductive reasoning, also known as induction or inductive logic, is a kind of reasoning that constructs or evaluates propositions that are abstractions of observations. It is commonly construed as a form of reasoning that makes generalizations based on individual instances...

, analytic/synthetic, necessary/contingent
Contingency (philosophy)
In philosophy and logic, contingency is the status of propositions that are neither true under every possible valuation nor false under every possible valuation . A contingent proposition is neither necessarily true nor necessarily false...


Use of the terms

The terms "a priori" and "a posteriori" are used in philosophy to distinguish two different types of knowledge, justification, or argument: 'a priori knowledge' is known independently of experience (conceptual knowledge), and 'a posteriori knowledge' is proven through experience. Thus, they are primarily used as adjective
In grammar, an adjective is a 'describing' word; the main syntactic role of which is to qualify a noun or noun phrase, giving more information about the object signified....

s to modify the noun
In linguistics, a noun is a member of a large, open lexical category whose members can occur as the main word in the subject of a clause, the object of a verb, or the object of a preposition .Lexical categories are defined in terms of how their members combine with other kinds of...

 "knowledge", or taken to be compound nouns that refer to types of knowledge (for example, "a priori knowledge"). However, "a priori" is sometimes used as an adjective to modify other nouns, such as "truth". Additionally, philosophers often modify this use. For example, "apriority" and "aprioricity" are sometimes used as nouns to refer (approximately) to the quality of being a priori."

The intuitive distinction

Although definitions and use of the terms have varied in the history of philosophy, they have consistently labelled two separate epistemological notions. The intuitive distinction between a priori and a posteriori knowledge is best seen in examples. To borrow from Jerry Fodor
Jerry Fodor
Jerry Alan Fodor is an American philosopher and cognitive scientist. He holds the position of State of New Jersey Professor of Philosophy at Rutgers University and is the author of many works in the fields of philosophy of mind and cognitive science, in which he has laid the groundwork for the...

 (2004), take, for example, the proposition expressed by the sentence, "George V reigned from 1910 to 1936." This is something (if true) that one must come to know a posteriori, because it expresses an empirical fact unknowable by reason alone. By contrast, consider the proposition, "If George V reigned at all, then he reigned for a finite period of time." This is something that one knows a priori, because it expresses a statement that one can derive by reason alone. As another example, that the equations of physics model our world is a posteriori knowledge, but the purely mathematical manipulation of those same equations is justified a priori.

Early uses

The phrases "a priori" and "a posteriori" are Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

 for "from what comes before" and "from what comes later" (or, less literally, "[from first principles, but] before experience" and "after experience"). They appear in Latin translations of Euclid
Euclid , fl. 300 BC, also known as Euclid of Alexandria, was a Greek mathematician, often referred to as the "Father of Geometry". He was active in Alexandria during the reign of Ptolemy I...

's Geometry, a work widely considered during the early modern period the model for precise thinking.

An early philosophical use of what might be considered a notion of a priori knowledge (though not called by that name) is Plato
Plato , was a Classical Greek philosopher, mathematician, student of Socrates, writer of philosophical dialogues, and founder of the Academy in Athens, the first institution of higher learning in the Western world. Along with his mentor, Socrates, and his student, Aristotle, Plato helped to lay the...

's theory of recollection
Innatism is a philosophical doctrine that holds that the mind is born with ideas/knowledge, and that therefore the mind is not a 'blank slate' at birth, as early empiricists such as John Locke claimed...

, related in the dialogue Meno
Meno is a Socratic dialogue written by Plato. It attempts to determine the definition of virtue, or arete, meaning virtue in general, rather than particular virtues, such as justice or temperance. The first part of the work is written in the Socratic dialectical style and Meno is reduced to...

(380 B.C.), according to which something like a priori knowledge is knowledge inherent, intrinsic
Intrinsic and extrinsic properties (philosophy)
An intrinsic property is a property that an object or a thing has of itself, independently of other things, including its context. An extrinsic property is a property that depends on a thing's relationship with other things...

 in the human mind.

George Berkeley
George Berkeley
George Berkeley , also known as Bishop Berkeley , was an Irish philosopher whose primary achievement was the advancement of a theory he called "immaterialism"...

, the Irish divine and philosopher outlined the distinction in A Treatise Concerning the Principles of Human Knowledge of 1710, though the terms were already well known by that time.

Immanuel Kant

Eighteenth-century German philosopher Immanuel Kant
Immanuel Kant
Immanuel Kant was a German philosopher from Königsberg , researching, lecturing and writing on philosophy and anthropology at the end of the 18th Century Enlightenment....

 (1781) advocated a blend of rationalist
In epistemology and in its modern sense, rationalism is "any view appealing to reason as a source of knowledge or justification" . In more technical terms, it is a method or a theory "in which the criterion of the truth is not sensory but intellectual and deductive"...

 and empiricist
Empiricism is a theory of knowledge that asserts that knowledge comes only or primarily via sensory experience. One of several views of epistemology, the study of human knowledge, along with rationalism, idealism and historicism, empiricism emphasizes the role of experience and evidence,...

 theories. Kant states, "although all our knowledge begins with experience, it does not follow that it arises from experience" According to Kant, a priori knowledge is transcendental
Transcendence (philosophy)
In philosophy, the adjective transcendental and the noun transcendence convey the basic ground concept from the word's literal meaning , of climbing or going beyond, albeit with varying connotations in its different historical and cultural stages...

, or based on the form of all possible experience, while a posteriori knowledge is empirical, based on the content of experience. Kant states, "... it is quite possible that our empirical knowledge is a compound of that which we receive through impressions, and that which the faculty of cognition supplies from itself (sensuous impressions giving merely the occasion)." Thus, unlike the empiricists, Kant thinks that a priori knowledge is independent of the content of experience; moreover, unlike the rationalists, Kant thinks that a priori knowledge, in its pure form, that is without the admixture of any empirical content, is knowledge limited to the deduction of the conditions of possible experience. These a priori, or transcendental conditions, are seated in one's cognitive faculties, and are not provided by experience in general or any experience in particular. Kant nominated and explored the possibility of a transcendental logic with which to consider the deduction of the a priori in its pure form. Concepts such as time
Time is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....

 and cause are counted among the list of pure a priori forms. Kant reasoned that the pure a priori forms are established via his transcendental aesthetic and transcendental logic. He claimed that the human subject would not have the kind of experience that it has were these a priori forms not in some way constitutive of him as a human subject. For instance, he would not experience the world as an orderly, rule-governed place unless time and cause were operative in his cognitive faculties. The claim is more formally known as Kant's transcendental deduction and it is the central argument of his major work, the Critique of Pure Reason
Critique of Pure Reason
The Critique of Pure Reason by Immanuel Kant, first published in 1781, second edition 1787, is considered one of the most influential works in the history of philosophy. Also referred to as Kant's "first critique," it was followed by the Critique of Practical Reason and the Critique of Judgement...

. The transcendental deduction does not avoid the fact or objectivity
Objectivity (philosophy)
Objectivity is a central philosophical concept which has been variously defined by sources. A proposition is generally considered to be objectively true when its truth conditions are met and are "mind-independent"—that is, not met by the judgment of a conscious entity or subject.- Objectivism...

 of time and cause, but does, in its consideration of a possible logic of the a priori, attempt to make the case for the fact of subjectivity
Subjectivity refers to the subject and his or her perspective, feelings, beliefs, and desires. In philosophy, the term is usually contrasted with objectivity.-Qualia:...

, what constitutes subjectivity and what relation it holds with objectivity and the empirical.

Johann Fichte

After Kant's death, a number of philosophers saw themselves as correcting and expanding his philosophy, leading to the various forms of German Idealism
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 politics of the Enlightenment...

. One of these philosophers was Johann Fichte. His student (and critic), Arthur Schopenhauer
Arthur Schopenhauer
Arthur Schopenhauer was a German philosopher known for his pessimism and philosophical clarity. At age 25, he published his doctoral dissertation, On the Fourfold Root of the Principle of Sufficient Reason, which examined the four separate manifestations of reason in the phenomenal...

, accused him of rejecting the distinction between a priori and a posteriori knowledge:

Relation to the analytic-synthetic

Several philosophers reacting to Kant sought to explain a priori knowledge without appealing to, as Paul Boghossian
Paul Boghossian
Paul Boghossian is professor of philosophy at New York University, where he held the chair for ten years . His research interests include epistemology, the philosophy of mind, and the philosophy of language....

 (MD) explains, "a special faculty...that has never been described in satisfactory terms." One theory, popular among the logical positivists
Logical positivism
Logical positivism is a philosophy that combines empiricism—the idea that observational evidence is indispensable for knowledge—with a version of rationalism incorporating mathematical and logico-linguistic constructs and deductions of epistemology.It may be considered as a type of analytic...

 of the early twentieth century, is what Boghossian calls the "analytic explanation of the a priori." The distinction between analytic and synthetic propositions was first introduced by Kant. While Kant's original distinction was primarily drawn in terms of conceptual containment, the contemporary version of the distinction primarily involves, as Quine
Willard Van Orman Quine
Willard Van Orman Quine was an American philosopher and logician in the analytic tradition...

 put it, the notions of "true by virtue of meanings and independently of fact." Analytic propositions are thought to be true in virtue of their meaning alone, while a priori synthetic propositions are thought to be true in virtue of their meaning and certain facts about the world. According to the analytic explanation of the a priori, all a priori knowledge is analytic; so a priori knowledge need not require a special faculty of pure intuition, since it can be accounted for simply by one's ability to understand the meaning of the proposition in question. In short, proponents of this explanation claimed to have reduced a dubious metaphysical faculty of pure reason to a legitimate linguistic notion of analyticity.

However, the analytic explanation of a priori knowledge has undergone several criticisms. Most notably, the American philosopher W. V. O. Quine (1951) argued that the analytic-synthetic distinction is illegitimate (see Quine's rejection of the analytic-synthetic distinction). Quine states: "But for all its a priori reasonableness, a boundary between analytic and synthetic statements simply has not been drawn. That there is such a distinction to be drawn at all is an unempirical dogma of empiricists, a metaphysical article of faith." While the soundness of Quine's critique is highly disputed, it had a powerful effect on the project of explaining the a priori in terms of the analytic.

Relation to the necessary/contingent

The metaphysical distinction between necessary and contingent truths has also been related to a priori and a posteriori knowledge. A proposition that is necessarily true
Modal logic
Modal logic is a type of formal logic that extends classical propositional and predicate logic to include operators expressing modality. Modals — words that express modalities — qualify a statement. For example, the statement "John is happy" might be qualified by saying that John is...

is one whose negation is self-contradictory (thus, it is said to be true in every possible world
Possible world
In philosophy and logic, the concept of a possible world is used to express modal claims. The concept of possible worlds is common in contemporary philosophical discourse and has also been disputed.- Possibility, necessity, and contingency :...

). Consider the proposition that all bachelors are unmarried. Theoretically, its negation, the proposition that some bachelors are married, is incoherent, because the concept of being unmarried (or the meaning of the word "unmarried") is part of the concept of being a bachelor (or part of the definition of the word "bachelor"). To the extent that contradictions are impossible, self-contradictory propositions are necessarily false, because it is impossible for them to be true. Thus, the negation of a self-contradictory proposition is supposed to be necessarily true. By contrast, a proposition that is contingently true is one whose negation is not self-contradictory (thus, it is said that it is not true in every possible world). As Jason Baehr states, it seems plausible that all necessary propositions are known a priori, because "[s]ense experience can tell us only about the actual world and hence about what is the case; it can say nothing about what must or must not be the case."

Following Kant, some philosophers have considered the relationship between aprioricity, analyticity, and necessity to be extremely close. According to Jerry Fodor, "Positivism
Logical positivism
Logical positivism is a philosophy that combines empiricism—the idea that observational evidence is indispensable for knowledge—with a version of rationalism incorporating mathematical and logico-linguistic constructs and deductions of epistemology.It may be considered as a type of analytic...

, in particular, took it for granted that a priori truths must be necessary...." However, since Kant, the distinction between analytic and synthetic propositions had slightly changed. Analytic propositions were largely taken to be "true by virtue of meanings and independently of fact", while synthetic propositions were not—one must conduct some sort of empirical investigation, looking to the world, to determine the truth-value of synthetic propositions.

Aprioricity, analyticity, and necessity have since been more clearly separated from each other. The American philosopher Saul Kripke
Saul Kripke
Saul Aaron Kripke is an American philosopher and logician. He is a professor emeritus at Princeton and teaches as a Distinguished Professor of Philosophy at the CUNY Graduate Center...

 (1972), for example, provided strong arguments against this position. Kripke argued that there are necessary a posteriori truths, such as the proposition that water is H2O (if it is true). According to Kripke, this statement is necessarily true (since water and H2O are the same thing, they are identical in every possible world, and truths of identity are logically necessary) and a posteriori (since it is known only through empirical investigation). Following such considerations of Kripke and others (such as Hilary Putnam
Hilary Putnam
Hilary Whitehall Putnam is an American philosopher, mathematician and computer scientist, who has been a central figure in analytic philosophy since the 1960s, especially in philosophy of mind, philosophy of language, philosophy of mathematics, and philosophy of science...

), philosophers tend to distinguish more clearly the notion of aprioricity from that of necessity and analyticity.

Kripke's definitions of these terms, however, diverge in subtle ways from those of Kant. Taking these differences into account, Kripke's controversial analysis of naming as contingent and a priori would best fit into Kant's epistemological framework by calling it "analytic a posteriori".

Thus, the relationship between aprioricity, necessity, and analyticity is not easy to discern. However, most philosophers at least seem to agree that while the various distinctions may overlap, the notions are clearly not identical: the a priori/a posteriori distinction is epistemological, the analytic/synthetic distinction is linguistic
Linguistics is the scientific study of human language. Linguistics can be broadly broken into three categories or subfields of study: language form, language meaning, and language in context....

, and the necessary/contingent distinction is metaphysical
Metaphysics is a branch of philosophy concerned with explaining the fundamental nature of being and the world, although the term is not easily defined. Traditionally, metaphysics attempts to answer two basic questions in the broadest possible terms:...


Further reading

  • Boghossian, P. & Peacocke, C., eds. (2000). New Essays on the A Priori, Oxford: Oxford University Press.
  • Descartes, René. (1641). "Meditations on First Philosophy". In Cottingham, et al. (eds.), The Philosophical Writings of Descartes, Cambridge University Press, 1984.
  • Fodor, Jerry. (2004). "Water's water everywhere", London Review of Books, Vol. 26, No. 20, dated 21 October 2004.
  • Greenberg, Robert. "Kant's Theory of A Priori Knowledge", Penn State Press, 2001 ISBN 0-271-02083-0
  • Heisenberg, Werner. (1958). "Physics and Philosophy: The Revolution in Modern Science", pp. 76–92. New York: Harper & Row.
  • Hume, David. (1777). An Enquiry concerning Human Understanding, Nidditch, P. N. (ed.), 3rd. ed., Oxford: Clarendon Press, 1975.
  • Jenkins, C. S. (2008). A Priori Knowledge: Debates and Developments, in Philosophy Compass 3.
  • Kant, Immanuel. (1783). Prolegomena to any Future Metaphysics
    Prolegomena to Any Future Metaphysics
    Prolegomena to Any Future Metaphysics That Will Be Able to Present Itself as a Science is one of the shorter works by the German philosopher Immanuel Kant...

    , Paul Carus (trans.). Online text
  • Kripke, Saul. (1972). "Naming and Necessity", in Semantics of Natural Language, edited by D. Davidson and G. Harman, Boston: Reidel. (Reprinted in 1980 as Naming and Necessity, Cambridge, MA: Harvard University Press.)
  • Leibniz, Gottfried. (1714). Monadology, in Philosophical Essays, edited and translated by Roger Ariew and Daniel Garber, Indianapolis: Hackett, 1989.
  • Locke, John. (1689). An Essay Concerning Human Understanding, Prometheus Books.
  • Palmquist, Stephen. (1987). "Knowledge and Experience - An Examination of the Four Reflective 'Perspectives' in Kant's Critical Philosophy", Kant-Studien 78:2, pp. 170–200; revised and reprinted as Chapter IV in Kant's System of Perspectives: An architectonic interpretation of the Critical philosophy. University Press of America, 1993.
  • Plato. (380 B.C.). Meno, in Plato: Complete Works, Cooper, J. M. (ed.), Indianapolis: Hackett, 1997.

External links