No Guarantee: Coherence, Rationality, and Fragmentation

According to anti-structuralists about rationality, such as Errol Lord and Benjamin Kiesewetter, incoherence is irrational because it guarantees a failure to respond to one's possessed reasons. For example, since having sufficient evidence for believing p entails not having sufficient evidence for believing not-p, it must be unreasonable to hold both beliefs. I argue that one of the most compelling explanations of how incoherence is psychologically possible, the fragmentation hypothesis, undermines this account of why it is irrational. When one's beliefs are fragmented, there is no guarantee that being reasonable is sufficient for being coherent.