The purpose of this work has been to examine critically the philosophical foundations on which the edifice of Soviet psychological theory has been built. In Chapter I we investigated the sources of this theory; these were seen to be two in number: the philosophical principles of Marxism-Leninism and the scientific theory of the great Russian physiological psychologists, particularly of I. P. Pavlov. Certainly, Pavlov's theories can scarcely be called philosophical; but as we have tried to show, the insistence on his ideas seems to have been primarily motivated by philosophical considerations; that is to say, it has been considered as a means to the construction of psychological science on the basis of Marxist-Leninist philosophy. To this end Pavlov's teaching on higher nervous activity is supposed to provide a scientific elucidation of the general Marxist-Leninist thesis that psychic phenomena are a function of the brain.