Error, Closure, and Epistemic Justification

Franz-Peter Griesmaier

The recent debate over the status of epistemic closure (the idea that knowledge is closed under known logical implication) is mainly driven by a shared desire to avoid skepticism, paired with radically different views on what the best way to do so is (for example, Dretske vs. Hawthorne, both 2005). However, closure is not only an issue in the fight against skepticism, but also in light of human epistemic fallibility. To see what’s at stake, I will raise the question whether justification is closed under justifiably believed logical implication. For actual human reasoners, the answer to this question will turn on the presence or absence of potential sources of inferential errors. Briefly, whether an agent is justified in believing p, which she believes to be a logical consequence of some subset B of her beliefs that she is justified in holding depends, among other things, on how likely it is that her belief that p is entailed by B is erroneous or not. I will end by applying my analysis to two cases in which error-related problems for closure turn out to play an important role: using simplicity considerations in theory choice, and using zombie-intuitions in arguments against physicalism.