The Experiential Defeasibility and Overdetermination of A Priori Justification

Abstract

The question whether a belief justified a priori is indefeasible in general and experientially indefeasible in particular has received different answers. 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 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 the overdetermination of justification. It will be argued that the prospects for this suggestion are brighter than for both of Thurow’s arguments.