||As paradigmatic symptoms of madness, delusions come in various forms and with diverse contents. The poster child of the current literature is the Capgras delusion: the patient may say with certainty that someone they are familiar with, such as their partner, is replaced by an imposter. Philosophical discussion of delusions tends to revolve around three groups of questions: (1) what are delusions? Are delusions beliefs or some other kinds of mental states? Suppose they are beliefs, what distinguish them from other forms of beliefs?; (2) How can we understand or explain the formation and maintenance of delusions? Where are the contents of delusions from? Why do patients adopt them in the first place? Why do patients not reject their delusions in light of counterevidence?; (3) How should we understand the relationship between patients’ delusions and their other mental states and actions? And what are the implications for our understanding of patients' rationality, agency, moral standing, legal status, and so on?