Abstract

This dissertation is about a priori justification and its relationship to experiential evidence. I begin with the assumption that a priori justification is justification that is independent of experience. It has been argued that putative examples of a priori justification are implausible because they are not, in any significant sense, independent of experience. My two central claims are that (a) a subject is plausibly justified a priori in believing a proposition only if the belief is not revisable on empirical grounds, which I will call the empirical unrevisability thesis; and (b) moderate rationalists can resist four empirical challenges considered by many to be decisive against the empirical unrevisability thesis. I begin by developing an account of experiential evidence that is neutral between rationalists and empiricists in order to make clear the distinction between a priori and a posteriori justification. I then argue that a moderate rationalist account of a priori justification is plausible only if the beliefs justified a priori are empirically unrevisable in a qualified sense. I then argue that four classical objections that putative cases of a priori justification are not independent of experience fail, namely, that they are revisable by some instances of contrary testimony, by mistakes in long proofs and memory, that a paradigm example of a priori knowledge was overturned by new evidence in physics, and that psychological data undermines the reliability of sources of a priori justification. I conclude that there is only one potentially threatening case, derived from neurological malfunction, and I leave the solution to this case to future research.