Hi! Welcome to “Dusty Phrases.” You will find a phrase below, in one ancient language or another, along with its English translation. You may also find the power to inspire your friends or provoke dread among your enemies.
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Latin:
A priori / posteriori
English:
From the earlier / from the later
Now here are two terms that I once struggled to understand and apply as a young student of philosophy. (This was an early warning, given to me by the planet earth, that not only was I not as smart as I had hoped I was, but also that I might understand life a little better if I had at least a loose working knowledge of Latin.)
You need not struggle, as I did in those long ago dark ages. We now live in the era of Wikipedia!
A priori (‘from the earlier’) and a posteriori (‘from the later’) are Latin phrases used in philosophy to distinguish types of knowledge, justification, or argument by their reliance on experience. A priori knowledge is independent from any experience. Examples include mathematics, tautologies and deduction from pure reason. A posteriori knowledge depends on empirical evidence. Examples include most fields of science and aspects of personal knowledge.
The terms originate from the analytic methods found in Organon, a collection of works by Aristotle. Prior analytics (a priori) is about deductive logic, which comes from definitions and first principles. Posterior analytics (a posteriori) is about inductive logic, which comes from observational evidence.
Both terms appear in Euclid‘s Elements and were popularized by Immanuel Kant‘s Critique of Pure Reason, an influential work in the history of philosophy. Both terms are primarily used as modifiers to the noun knowledge (i.e., a priori knowledge). A priori can be used to modify other nouns such as truth. Philosophers may use apriority, apriorist and aprioricity as nouns referring to the quality of being a priori.
Examples
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
Consider the proposition: “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 distinction
Several philosophers, in reaction to Immanuel Kant, sought to explain a priori knowledge without appealing to, as Paul Boghossian explains, “a special faculty [intuition] … 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 considered true by virtue of their meaning alone, while a posteriori propositions by virtue of their meaning and of 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; it is 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.” 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.
Separation
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 diverge in subtle ways from Kant’s. 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 easy to discern. 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.
Ugh. As it turns out, I remain not as smart as I once hoped I was. I’m going to have to work on “epistemological” and what that’s all about…
However, I think it is correct to say that a priori is an adjective describing knowledge which is derived solely from reason or logic (‘from the earlier” roughly meaning “before observation”) where as posteriori is an adjective describing knowledge based on observation (“from the later” roughly meaning “from after observation.”)
Now go read Kant and Kripke and enjoy.
