Delusions and hallucinations present a challenge to traditional epistemology by allowing two people’s experiences of the world to be vastly different to each other. Traditional objective realism assumes that there is a mind-independent objective world of which people gain knowledge through experience. However, each person only has direct access to his or her own subjective experience of the world, and so neither can be certain that his or her experience represents an objective world more accurately than the other’s. This essay (...) proposes an intersubjective account of psychosis, which avoids this sceptical attack on objective certainty by considering reality not at the level of an objective mindindependent world, but at the level of peoples’ shared experiences. This intersubjective hypothesis is developed further, with reference to Husserl’s concept of multiple lifeworlds, into a relativistic account. The implication on the social role of psychiatry is also explored. (shrink)