The prominence of the a priori within traditional epistemology is largely due to the influence of Immanuel Kant's Critique of Pure Reason (1965), where he introduces a conceptual framework that involves three distinctions: the epistemic distinction between a priori and empirical (or a posteriori) knowledge; the metaphysical distinction between necessary and contingent propositions; and the semantic distinction between analytic and synthetic propositions. Within this framework, Kant poses four questions:

1. What is a priori knowledge?
2. Is there a priori knowledge?
3. What is the relationship between the a priori and the necessary?
4. Is there synthetic a priori knowledge?

These questions remain at the center of the contemporary debate.

Kant maintains that a priori knowledge is "independent of experience," contrasting it with a posteriori knowledge, which has its "sources" in experience (1965, p. 43). He offers two criteria for a priori knowledge, necessity and strict universality, which he claims are...