At the turn of the century Kraepelin brought together the disparate syndromes of hebephrenia, dementia paranoides, and catatonia under the rubric of dementia praecox. At the same time he crystallized the concept of manic-depressive illness as an entity discrete and separate from the former syndrome. In the years since Kraepelin's classification first came to be adopted, the definitions and descriptions of these two major disorders have undergone many changes. In an attempt to comprehend the meaning and the mechanism of the psychoses, Bleuler was drawn by the emergent theories of psychoanalysis to extend Kraepelin's clinical observations into the realm of psychology. He renamed dementia praecox the schizophrenias, thus emphasizing his idea that the splitting of associative processes was a fundamental feature of the syndrome; and he added the subcategory of simple schizophrenia. American psychiatry, dominated until recently by psychoanalytic concepts, has been influenced more by Bleulerian than Kraepelinian contributions. However, it has not restricted itself to Bleulerian notions. As Kety (1980) remarked in his Maudsley Lecture, great liberties have been taken with the syndrome of schizophrenia; the essential features have been altered, primarily by an expansion of its boundaries.