Delusions and three myths of irrational belief

This chapter addresses the contribution that the delusion literature has made to the philosophy of belief. Three conclusions will be drawn: (1) a belief does not need to be epistemically rational to be used in the interpretation of behaviour; (2) a belief does not need to be epistemically rational to have significant psychological or epistemic benefits; (3) beliefs exhibiting the features of epistemic irrationality exemplified by delusions are not infrequent, and they are not an exception in a largely rational belief system. What we learn from the delusion literature is that there are complex relationships between rationality and interpretation, rationality and success, and rationality and knowledge.