The Experiential Defeasibility and Overdetermination of A Priori Justification

In a recent and interesting paper “Experientially Defeasible A Priori Justification,” Joshua Thurow argues that many a priori justified beliefs are defeasible by experience. The argument takes the form of an objection against Albert Casullo’s recent book, A Priori Justification, where Casullo, according to Thurow, denies that if a justified belief is non-experientially defeasible, then that belief is also experientially defeasible. This paper critically examines Thurow’s two arguments in the first two sections I–II. In the last section, III, an alternative line of argument for Thurow’s thesis is suggested that employs other parts of the framework that Casullo provides—especially the thesis of overdetermination of justification. It will be argued that the prospects for this suggestion are brighter than for bothof Thurow’s arguments