Agonies and ecstasies
William James considered an hallucination to be ‘as good and true a sensation as if there were a real object there’, except that the ‘object happens to be not there, that is all’ — an admirable definition, and a favourite of Oliver Sacks, the eminent neurologist, who has written what he calls ‘a sort of natural history or anthology of hallucinations’, which he thinks are an essential part of the human condition. He excludes schizophrenic hallucinations, on the grounds that they demand separate consideration, but includes every other kind.