A priori and a posteriori

"A priori" and "A posteriori" redirect here. For other uses, see A priori (disambiguation) and A posteriori (disambiguation).

A priori and a posteriori ('from the earlier' and 'from the later', respectively) are Latin phrases used in philosophy to identify two types of knowledge, justification, or argument, characterized by the use of empirical evidence found in experience (a posteriori) or the lack thereof (a priori). The terms feature prominently in epistemology, where they are used to distinguish between conclusions reached independently of experience (such as those of logic, mathematics, or metaphysics) and conclusions which depend on experience (such as those of science or perception). Thus, the two kinds of knowledge, justification, or argument, may be glossed:

• A priori: knowledge, justifications, or arguments that exist independently from experience. Examples include mathematics (e.g. 3 + 2 = 5); tautologies (e.g. "all bachelors are unmarried"); and deduction from pure reason (e.g., ontological proofs).
• A posteriori: knowledge, justifications, or arguments that depend on experience or empirical evidence. Examples include most aspects of science and personal knowledge.

Although definitions and use of the terms have varied in the history of philosophy, they have consistently labeled two separate epistemological notions. Both terms are primarily used as modifiers to the noun "knowledge" (i.e. 'a priori knowledge'). However, a priori can also be used to modify other nouns, such as "truth." Philosophers also may use apriority, apriorist, and aprioricity as nouns referring to the quality of being a priori. The terms were first popularized by Immanuel Kant through his Critique of Pure Reason (1781, 1st ed.; 1787, 2nd ed.), one of the most influential works in the history of philosophy. However, in Latin, the two terms appear in translations of Euclid's Elements (c. 300 BC), a work widely considered to be the model for precise thinking during the early European modern period.

There are several related distinctions which are frequently used along with epistemology's distinction between a priori and a posteriori: analytic/synthetic, which is a distinction in the philosophy of language; necessary/contingent, which is a distinction in metaphysics; and deductive/inductive, which is a distinction in logic.

Examples

The intuitive distinction between a priori and a posteriori knowledge (or justification) is best seen via examples, as below:

A priori

Consider the proposition: "If George V reigned at least four days, then he reigned more than three days." This is something that one knows a priori, because it expresses a statement that one can derive by reason alone.

A posteriori

Compare the above with the proposition expressed by the sentence: "George V reigned from 1910 to 1936." This is something that (if true) one must come to know a posteriori, because it expresses an empirical fact unknowable by reason alone.

Aprioricity, analyticity, and necessity

Relation to the analytic-synthetic

Further information: Analytic-synthetic distinction

Several philosophers, in reaction to Immanuel Kant, sought to explain a priori knowledge without appealing to, as Paul Boghossian explains, "a special faculty…that has never been described in satisfactory terms." One theory, popular among the logical positivists of the early 20th 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 his original distinction was primarily drawn in terms of conceptual containment, the contemporary version of such distinction primarily involves, as American philosopher W. V. O. Quine 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 posteriori 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. More simply, proponents of this explanation claimed to have reduced a dubious metaphysical faculty of pure reason to a legitimate linguistic notion of analyticity.

The analytic explanation of a priori knowledge has undergone several criticisms. Most notably, Quine argues that the analytic–synthetic distinction is illegitimate:

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 truths and contingent truths

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 is one in which its negation is self-contradictory. Thus, it is said to be true in every possible world. For example, considering the proposition "all bachelors are unmarried:" its negation (i.e. the proposition that some bachelors are married) is incoherent due to the concept of being unmarried (or the meaning of the word "unmarried") being tied to 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 as it is impossible for them to be true. The negation of a self-contradictory proposition is, therefore, supposed to be necessarily true.

By contrast, a proposition that is contingently true is one in which its negation is not self-contradictory. Thus, it is said not to be true in every possible world. As Jason Baehr suggests, 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, in particular, took it for granted that a priori truths must be necessary." However, since Kant, the distinction between analytic and synthetic propositions has 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

Aprioricity, analyticity, and necessity have since been more clearly separated from each other. American philosopher Saul Kripke (1972), for example, provides strong arguments against this position, whereby he contends that there are necessary a posteriori truths. For example, the proposition that water is H₂O (if it is true): According to Kripke, this statement is both necessarily true, because water and H₂O are the same thing, they are identical in every possible world, and truths of identity are logically necessary; and a posteriori, because it is known only through empirical investigation. Following such considerations of Kripke and others (see Hilary Putnam), philosophers tend to distinguish the notion of aprioricity more clearly 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, according to Stephen Palmquist, best fit into Kant's epistemological framework by calling it "analytic a posteriori." Aaron Sloman presented a brief defence of Kant's three distinctions (analytic/synthetic, apriori/empirical, and necessary/contingent), in that it did not assume "possible world semantics" for the third distinction, merely that some part of this world might have been different.

The relationship between aprioricity, necessity, and analyticity is not found to be 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,; and the necessary/contingent distinction is metaphysical.

History

Early uses

The term a priori is Latin for 'from what comes before' (or, less literally, 'from first principles, before experience'). In contrast, the term a posteriori is Latin for 'from what comes later' (or 'after experience').

They appear in Latin translations of Euclid's Elements, of about 300 BC, a work widely considered during the early European modern period as 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's theory of recollection, related in the dialogue Meno (380 BC), according to which something like a priori knowledge is knowledge inherent, intrinsic in the human mind.

Albert of Saxony, a 14th-century logician, wrote on both a priori and a posteriori.

G. W. Leibniz introduced a distinction between a priori and a posteriori criteria for the possibility of a notion in his (1684) short treatise "Meditations on Knowledge, Truth, and Ideas". A priori and a posteriori arguments for the existence of God appear in his Monadology (1714).

George Berkeley outlined the distinction in his 1710 work A Treatise Concerning the Principles of Human Knowledge (para. XXI).

Immanuel Kant

The 18th-century German philosopher Immanuel Kant (1781) advocated a blend of rationalist and empiricist theories. Kant says, "Although all our cognition begins with experience, it does not follow that it arises [is caused by] from experience." According to Kant, a priori cognition is transcendental, or based on the form of all possible experience, while a posteriori cognition is empirical, based on the content of experience:

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 [sense data] giving merely the occasion [opportunity for a cause to produce its effect].

Contrary to contemporary usages of the term, Kant believes that a priori knowledge is not entirely independent of the content of experience. Unlike the rationalists, Kant thinks that a priori cognition, in its pure form, that is without the admixture of any empirical content, is 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 (although an argument exists that a priori intuitions can be "triggered" by experience).

Kant nominated and explored the possibility of a transcendental logic with which to consider the deduction of the a priori in its pure form. Space, time and causality are considered pure a priori intuitions. Kant reasoned that the pure a priori intuitions 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, a person would not experience the world as an orderly, rule-governed place unless time, space and causality were determinant functions in the form of perceptual faculties, i. e., there can be no experience in general without space, time or causality as particular determinants thereon. 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. The transcendental deduction argues that time, space and causality are ideal as much as real. In consideration of a possible logic of the a priori, this most famous of Kant's deductions has made the successful attempt in the case for the fact of subjectivity, 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. One of these philosophers was Johann Fichte. His student (and critic), Arthur Schopenhauer, accused him of rejecting the distinction between a priori and a posteriori knowledge:

... Fichte who, because the thing-in-itself had just been discredited, at once prepared a system without any thing-in-itself. Consequently, he rejected the assumption of anything that was not through and through merely our representation, and therefore let the knowing subject be all in all or at any rate produce everything from its own resources. For this purpose, he at once did away with the essential and most meritorious part of the Kantian doctrine, the distinction between a priori and a posteriori and thus that between the phenomenon and the thing-in-itself. For he declared everything to be a priori, naturally without any evidence for such a monstrous assertion; instead of these, he gave sophisms and even crazy sham demonstrations whose absurdity was concealed under the mask of profundity and of the incomprehensibility ostensibly arising therefrom. Moreover, he appealed boldly and openly to intellectual intuition, that is, really to inspiration.

— Schopenhauer, Parerga and Paralipomena, Vol. I, §13

See also

• Abductive reasoning
• A priori probability
• Deductive reasoning
• Inductive reasoning
• Relativized a priori
• Tabula rasa
• Transcendental empiricism
• Transcendental hermeneutic phenomenology
• Transcendental nominalism

References

Sources

• Baehr, Jason S. (2006). "A Priori and A Posteriori". Internet Encyclopedia of Philosophy.
• Boghossian, Paul Artin (2003) [1997]. "14: Analyticity". In Hale, Bob; Wright, Crispin (eds.). A Companion to the Philosophy of Language. Blackwell Companions to Philosophy. Malden, MA: Blackwell Publishing. ISBN 978-0631213260.
• Fodor, Jerry (1998). Concepts: Where Cognitive Science Went Wrong. New York, NY: Oxford University Press. ISBN 978-0198236368.
• Hoiberg, Dale H., ed. (2010). "a priori knowledge". Encyclopædia Britannica. Vol. I: A-Ak - Bayes (15th ed.). Chicago, Illinois: Encyclopædia Britannica, Inc. ISBN 978-1-59339-837-8.
• Kant, Immanuel (1781). Kritik der reinen Vernunft [Critique of Pure Reason]. Im Insel-Verlag.
• Kitcher, Philip (2001). "A Priori Knowledge Revisited". In Boghossian, Paul; Peacocke, Christopher (eds.). New Essays on the A Priori. Oxford, England: Oxford University Press. ISBN 978-0199241279.
• Palmquist, Stephen (December 1987). "A Priori Knowledge in Perspective: (II) Naming, Necessity and the Analytic A Posteriori". The Review of Metaphysics. 41 (2): 255–282.
• Quine, Willard Van Orman (1951). "Two Dogmas of Empiricism". The Philosophical Review. 60 (1): 20–43. doi:10.2307/2181906. JSTOR 2181906.
• Sommers, Tamler (March 2003). Jarman, Casey (ed.). "Galen Strawson (interview)". Believer Magazine. 1 (1). San Francisco, CA: McSweeney's McMullens. Retrieved 10 July 2013.

Further reading

• Descartes, René (1641). In Cottingham; et al. (eds.). Meditationes de prima philosophia, in qua Dei existentia et animæ immortalitas demonstratur [Meditations on First Philosophy]. Archived from the original on 15 July 2013. Retrieved 25 August 2006.
• — (1984). The Philosophical Writings of Descartes. Vol. 2. Cambridge, UK: Cambridge University Press. ISBN 978-0521288088.
• Fodor, Jerry (21 October 2004). "Water's Water Everywhere". London Review of Books. 26 (21)..
• Greenberg, Robert (2001). Kant's Theory of a Priori Knowledge. University Park, PA: Penn State Press. ISBN 978-0271020839. Archived from the original on 1 September 2006. Retrieved 30 May 2007.
• Heisenberg, Werner (2007) [1958]. Physics and Philosophy: The Revolution in Modern Science. New York, NY: Harper Perennial Modern Classics. pp. 76–92. ISBN 978-0061209192.
• Hume, David (2008) [1777]. Millican, Peter (ed.). An Enquiry concerning Human Understanding. Oxford, UK: Oxford university Press. ISBN 978-0199549900. Archived from the original on 7 October 2008. Retrieved 28 August 2006.
• Jenkins, C. S. (May 2008). "A Priori Knowledge: Debates and Developments". Philosophy Compass. 3 (3): 436–450. doi:10.1111/j.1747-9991.2008.00136.x. Archived from the original on 5 January 2013.
• Kant, Immanuel (1783). Prolegomena zu einer jeden künftigen Metaphysik [Prolegomena to any Future Metaphysics]. Archived from the original on 31 August 2000.
• Kripke, Saul (2013) [1972]. "Naming and Necessity". Semantics of Natural Language. Synthese Library (2nd ed.). Springer. ISBN 978-9027703101.
• Leibniz, Gottfried (1976) [1714]. "Monadology". In Loemker, Leroy E. (ed.). Philosophical Papers and Letters: A Selection. Synthese Historical Library. Vol. 2 (2nd ed.). Dordrecht: Kluwer Academic Publishers. ISBN 978-9027706935.
• Locke, John (1689). Nidditch, Peter H. (ed.). An Essay Concerning Human Understanding. Clarendon Edition of the Works of John Locke. Oxford, UK: Oxford University Press. ISBN 978-0198245957. Archived from the original on 29 August 2006. Retrieved 29 August 2006.
• Palmquist, Stephen (September 1987). "A Priori Knowledge in Perspective: (I) Mathematics, Method and Pure Intuition". The Review of Metaphysics. 41 (1): 3–22.
• Plato (1997) [380 B.C.]. "Meno". In Cooper, John M.; Hutchinson, D. S. (eds.). Plato: Complete Works. Indianapolis, IN: Hackett Publishing Co. ISBN 978-0872203495.

External links

• Zalta, Edward N. (ed.). "A Priori Justification and Knowledge". Stanford Encyclopedia of Philosophy.
• A priori and a posteriori at the Indiana Philosophy Ontology Project
• A priori and a posteriori at PhilPapers
• "A priori and a posteriori". Internet Encyclopedia of Philosophy.
• A priori / a posteriori — in the Philosophical Dictionary online.
• "Rationalism vs. Empiricism" — an article by Peter Markie in the Stanford Encyclopedia of Philosophy.