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Philosophy

Viv Joseph

Hallucinations and delusions can be symptoms of mental ill health. Visual hallucinations - seeing things that are not really there - pose particular philosophical problems in relation to how we understand normal visual experience. Hallucinations can seem as real as normal visual experience to the person experiencing them, which raises doubts about our ability to determine whether or not our own visual experiences are real.


A simple characterisation of delusions is that they are abnormal ideas that are the result of disturbed judgement. One of the challenges posed by delusions is that typically they cannot be influenced by evidence or reasoning. A delusional person who believes his wife is an imposter will not be influenced by evidence and reasoning to the contrary. This sort of irrationality has made some philosophers question the extent to which we can make sense of someone who is delusional, and poses practical and theoretical problems for medical staff and the wider public.

This session will introduce and explore some of the philosophical issues that hallucinations and delusions give rise to.

All the reading for this week is available for download/access from the Resources page (sign-in necessary).