The binary relationship between ‘intellectual disability’ and ‘mental illness’ is widely regarded as self-evident and long-established. This chapter demonstrates that the historical, and continuing, relationship between intellectual disability and psychiatry is, in fact, ambiguous and inconsistent. Beginning with the nosology of William Cullen in the latter part of the seventeenth century, the chapter explores the dispersal of madness across all the branches of disease and illness. The advent of alienism and Pinel’s nosology of madness, at the beginning of the eighteenth century, produced much flatter conceptual structures, in which idiocy was one of the various forms of madness. As psychiatry developed, the position of idiocy shifted. Maudsley located it in a separate branch, though still not separated in a binary manner from insanity. Lastly, the nosology of the neurologist Spitzka became more nuanced and layered, though still without a binary separation of idiocy. The chapter takes the view that the lack of any consistent underlying paradigm in psychiatry will continue to make the presence and position of intellectual disability impossible to fix. Psychoanalytic and neo-Jasperian psychiatry thoroughly exclude it as an object of investigation

in Intellectual disability