During the late twentieth century, drawing on C. P. Snow’s well-known concept of a “two cultures” divide between scientists and humanists, many psychologists identified polarizing divergences in their discipline. This essay traces how purported professional divides affected the understanding and management of mental retardation in clinical psychology. Previous work in the history of science has compared the differing cultures of disciplines, demonstrating that there is no one, unified science. Through an examination of multiple “two cultures” divides within the discipline of (...) psychology, the essay demonstrates that perceived divergences in the field were animated by considerations of professional identity, ambitions, and goals. It argues that differing views among clinical psychologists about mental retardation, and crucially the localization of its causes—in individual bodies, minds, and genomes or within social institutions—reflected their position among the multiple “cultures” of psychology. References to Snow’s two cultures spanned the late twentieth-century scientific and clinical literature and were often used to encourage a conversation about the nature and goals of research in a field. In considering these purported “two cultures” divides, the essay proposes that historians of science must take care to look beyond constructed polarities, to instead analyze the resulting discussions about professional training and purpose. (shrink)