Modern psychiatry had its origins in the Enlightenment in two major phases. From the late 18th century, anthropological understanding, in the sense of understanding human beings as psychophysical entities, saw madness as a “private truth outside the common horizon of reason”. Psychiatry’s role was to detect such delusional thinking. However, by mid-19th century, positivism saw mental illness as a dysfunctional natural mechanistic process. Foucault’s analysis critiques the marginalisation of the anthropological attitude by positivism in psychiatry.
As John says, abnormality in general became the object of psychiatric knowledge, not merely delusion. I’m not sure if I agree with what John seems to imply that the potential this perspective creates to explode “the diagnostic field uncontrollably” merely relates to a positivistic attitude to mental illness. My previous post highlighted how Foucault in the History of madness recognised that mental illness already incorporated neurosis by the end of the 18th century. But in the 19th century, the development of pathological abnormality undermined the concept of functional disorder (see another previous post). In fact, positivism encouraged speculation about the biological basis of neurosis, such as Beard’s neurasthenia (see previous post).
I would also emphasise the importance of anatomoclinical understanding in Foucault’s account more than John seems to do (see eg. previous post). After all, Foucault moved on to the Birth of the clinic after the History of madness. He must have done this because he wanted to understand how the development of the idea of illness as physical pathology was implicated in psychiatry.
As John says, Foucault is actually “sceptical of the anti-psychiatric quest for non-oppressive modes of psychiatric power and the humanist and postmodern efforts to moralise or relativise psychiatric truth”. Instead, his critique highlights the value of the anthropological outlook of alienists in the origins of modern psychiatry. Fundamentally, he did not think mental illness should be reduced to brain disease (see yet another previous post).