A nineteenth-century psychiatric term for madness that was taken up by psychoanalysis to designate severe mental disorders (e.g. schizophrenia), which it contrasted with the less severe disorders of neurosis. In general, psychoanalysis regards psychosis as untreatable because it has as its main symptom the complete breakdown of communication, thereby making the talking cure impossible. Yet, as the work of Lacan, Jacques makes plain, psychoanalysis also regards psychosis as an incredibly important phenomenon from the point of view of studying how the psychical apparatus functions. Lacanâs theory of the genesis of psychosis hinges on the failure of the field process and the foreclosure of Name-of-the-Father, with the result that symbolic order is not properly formed and the subject is locked into a nightmarish world dominated by the imaginary. Unable to distinguish between the real and the unreal, the psychotic subject suffers delusional episodes that can make life extremely difficult for them. Deleuze, Gilles and Guattari, FĂ©lix reject the psychoanalytic explanation of the genesis of psychosis---in their view, its genesis can only be organic, i.e. the result of physiological changes in the brain itself. As a result, their work offers no theory for the treatment of psychosis; rather, it concentrates on adapting the world (and not the âpatientâ) to its symptoms.