During the past few years there has been a rapid growth of interest in the sociological history of psychiatry. Prior to this, the history of psychiatry had been left largely to the psychiatric historian, who tended to proceed, as Thomas Szasz claimed, ‘as a socially neutral person, discovering the historical “facts” when in truth, he is a psychiatric propagandist, actively shaping the image of his discipline’ (1). Writers such as Michel Foucault, Vieda Skultans, Andrew Scull, David Rothman, Klaus Doerner, and Szasz himself have attempted to underline, as Skultans says, ‘the specific uses to which psychiatry has been put in the past, in order to make a more general claim about the nature of psychiatry as such’ (2). This aim, however, is not always made fully explicit (3). In this paper it will be argued that psychiatry, viewed as a historically constituted social activity, was characterised by a dualism. It was constituted by a medical or curative model of practice, in that psychiatry developed as a branch of medicine. Yet the ‘diseases’ which psychiatrists have historically come to regard as part of their field competence are distinguished by at least two criteria: first, their symptoms consist primarily of actions that are highly inappropriate to their social context; secondly, that their etiology is ambiguous. It will be argued here that an ambiguity regarding the etiology of mental disorder, which is often seen as both physically and psychologically caused, was central to psychiatric discourse.