Delusions are often defined as fixed false beliefs. They run contrary to common sense or counter-evidence that would convince any rational person, like the idea that aliens are communicating with me through a radio chip implanted in my brain, or the thought that my father has been replaced by an imposter, albeit an imposter that is identical to my father in every discernible way. But why do people acquire delusions in the first place? Philosophy is often thought to be a rational activity of the highest order. Maybe philosophers can shed some light on what is going wrong with the reasoning of people who have delusions?

Today’s consultation is with philosopher Matthew Parrott, Birmingham Fellow in Philosophy at the University of Birmingham (formerly at King’s College London).

This episode is published jointly with the Canadian Medical Association Journal. Visit the Journal website to read an accompanying article by Dr. Parrott, “Delusional possibilities” (2019, 191: E867-E868).