Abstract

Kengo Miyazono’s Delusions and Beliefs: A Philosophical Inquiry is an attempt to provide a unified account of the nature, pathology, and etiology of delusions. The strength of his book resides in the clarity of arguments and its consistent adoption of a biological explanation of delusions, based on teleo-functionalism about mental states. However, there are some weaknesses in each of his arguments regarding the nature, pathology, and etiology of delusions. Regarding the nature of delusions, teleo-functionalism makes it difficult to confirm that delusions are beliefs. Regarding the pathology of delusions, I suggest that the existence of harmful malfunction is a necessary but not a sufficient condition for a belief to be considered pathological, and that additional evidence is needed to justify the separation of the belief and the holder’s personhood. Regarding the etiology, it is not reasonable to incorporate the prediction error theory into a kind of two-factor theory. Therefore, the details of his arguments require further modification.