 In the philosophy of mind and the philosophy of psychology, the study of delusions raises conceptual questions about intentionality, rationality, agency, and self-knowledge. Moreover, it invites us to reconsider how perception, cognition, affect, and intentional behavior interact. There have been various attempts to understand the cognitive processes responsible for the formation of delusions, based on the assumption, widely shared in cognitive neuropsychology, that understanding such processes can lead to the formulation of more empirically sound theories of neurotypical cognition (see Marshall and Halligan 1996, pp. 5–6; Langdon and Coltheart 2000, pp. 185–6). Understanding how delusions come about, whether they are responses to unusual experiences, and whether a reasoning deficit is responsible for their development can shed light on standard processes of belief formation. One basic question is what comes first, perceptual experience or belief (see Campbell 2001). Are delusions frames of mind that, once adopted, alter our way of seeing the world? Or do they emerge as explanations for our unusual perceptual experiences? Does having delusions signal a breakdown of rationality, and if so, what makes us irrational when we sincerely report a delusional belief?