a priori

A term applied to statements to reflect the status of our knowledge of their truth (or falsehood). It means literally 'from what comes before', where the answer to 'before what?' is understood to be 'experience'. Loosely, one may speak of knowing some truth 'a priori' where it is possible to infer the truth without having to experience the state of affairs in virtue of which it is true, but in strict philosophical usage, an a priori truth must be knowable independently of all experience. Kant held that the criteria of a priori knowledge were

(i) necessity, for 'experience teaches us that a thing is so and so, but not that it cannot be otherwise', and
(ii) universality, for all experience can confer on a judgement is 'assumed and comparative universality through induction'.

Gottlob Frege stressed that the issue was one of justification, and defined an a priori truth as one whose proof rests exclusively on general laws which neither need nor admit of proof, while a truth which cannot be proved without appeal to assertions about particular objects is a posteriori.

Statements such as 'A vixen is a fox', whose truth is analytic, are accorded a priori status without dispute. Kant held that in addition truths of arithmetic and geometry, and such statements about the natural world as 'Every event has a cause', were not analytic but nevertheless had the hallmarks of being a priori. The central question that his philosophy addressed was how such synthetic a priori truths were possible, whereas the strategy of his 20th-century empiricist critics was to argue that there are no a priori truths that are not analytic.

(Published 1987)

— J. E. Tiles

Bibliography
• Frege, G. (1959). The Foundations of Arithmetic. Trans. J. L. Austin, section 3.
• Kant, I. (1929). The Critique of Pure Reason. Trans. N. Kemp-Smith, Preface and Introduction.

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