Psychosis is often characterized as 'loss of contact with reality.' Three questions. (1) What is this 'reality' of which they speak? (2) Does anybody (even psychatrists) really know enough about this 'reality' to be able competently to deliver a diagnosis under that characterization? (3) What is this 'contact' of which they speak

Your question engages at least three areas of philosophy: metaphysics, epistemology, and philosophy of mind. The answers are as deep and detailed as those areas, i.e., as deep and detailed as you want to go. But maybe a short answer will do for now. Someone claims, apparently sincerely, that the government is controlling him by means of radio signals sent to his dental fillings. (1) He's "in contact with reality," in that respect, only if the government is in fact doing what he claims. (2) There's no good reason to believe it is, and good reasons to believe it isn't (his relative unimportance, the nature of radio signals, the nature of neurons, etc.). If we're justified in drawing conclusions about any empirical issue, I'd say we're therefore justified in concluding that he isn't in contact with reality in that respect. (3) I'm no psychiatrist, but my sense is that losing "contact" with reality requires being impervious to evidence in a special way; not just any false belief, even if persistently held, makes one psychotic. There's clearly room here for controversy! You can find some of it discussed at this link.

It is a good question. It is possible that a sane personmight believe that the government is controlling him by means of radio signalssent to his dental filling when in fact that is far from the truth, and that apsychotic person might believe such a thing and the belief be true. Someapparently sane thinkers believe that the commonsense world as we normallythink of it, as populated with people, teeth, tables, chairs and governments isnot real. Notions like that of a government are too vague and confused to pickout genuine denizens of reality. Only science tells us what is real. Ifthat or some other skeptical hypothesis turns out to be right, then perhapsmost of us do not have contact with reality in respect of most of our beliefs.But that doesn't mean that we are all psychotic. We might be very badjudges about the justification of beliefs about empirical issues. So perhaps judgementsabout whether someone is psychotic should not require us to make judgements inrelation to other, tangential empirical issues. Similarly it is not clear thatpsychosis is best understood in terms of imperviousness to evidence of acertain kind. Evidence is an epistemic notion bound up with the idea of truth,of a way of cognitive functioning that is likely to arrive at true beliefs andavoid false ones. Questions about ways in which one ought not to be impervious to evidence seem to be questions forscience and philosophy of science, not psychiatry, psychology and philosophy ofpsychology or medicine. So perhaps the kind of cognitive disorder orabnormality associated with psychosis, if there is any such thing, is best notunderstood in terms of loss of contact with reality at all, but rather in somequite different way

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