This highly readable translation of the major works of the 18th- century philosopher Etienne Bonnot, Abbe de Condillac, a disciple of Locke and a contemporary of Rousseau, Voltaire, and Diderot, shows his influence on psychiatric diagnosis as well as on the education of the deaf, the retarded, and the preschool child. Published two hundred years after Condillac's death, this translation contains treatises which were, until now, virtually unavailable in English: A Treatise on Systems, A Treatise of the Sensations, Logic.