THE DIFFERENT KINDS OF A PRIORI (1944)

I am going to distinguish three kinds of a priori: the formal or analytic a priori, the functional a priori, and the material a priori. With these three kinds of a priori there are associated three types of necessity: formal or logical necessity, as characterizing logical truths, whether the latter be called “tautologies,” as by logical positivists, or “truths of reason,” as by Leibniz; functional necessity (Aristotle’s “hypothetical necessity”), predicable of conceptual means in relation to objectives or ends of inquiry; and the kind of necessity that one might call psychological, if it were not the case that the chief proponents of this kind, the kind of necessity that is traditionally defined by self-evidence or the inconceivability of the opposite, are explicitly opposed to “psychologism” in logic (I am referring to the school of phenomenology, or “Gegenstandstheorie,” as founded by Husserl and Meinong).