Adam Phillips writes:
Descriptions of mental illness depend on what a society regards as a desirable form of exchange. Behaviour is seen as a symptom (or a crime) rather than a foible or a talent when things deemed to be essential – sex, words, money – are being exchanged in a particularly disturbing way, or not being exchanged at all. Sex with children is unequivocally wrong, and possibly an illness, while exchanging sex for money is merely controversial. In the relatively recent past there was something wrong with men exchanging semen with each other, but nothing wrong with men and women exchanging words with God. Now, for some of the authorities, exchanging words with people who are not there, or using words in a way that makes exchange extremely difficult, or not using words at all, as in psychosis, is an illness or at least a problem. Because these are simply agreements between people and not divine fiats or laws of nature – because diagnoses are now understood to be more or less authoritative forms of consensus – our beliefs about these things are up for grabs in a way that they haven’t been before.