Joshua C. Thurow

In his recent book Albert Casullo rejects the claim that if a belief is defeasible by non-experiential evidence then it is defeasible by experiential evidence. This claim is a crucial premise in a simple argument for the experiential defeasibility of a priori justification. I defend the premise against Casullo's objection, the main problem with which is that he does not take into account the evidential role of multiple corroborating sources of testimony. I conclude that the crucial premise is true and that the simple argument is sound; thus many of our a priori justified beliefs are experientially defeasible