Under the impact of new developments in science, ideas in all fields are undergoing rapid change. This is especially true of the twentieth-century conception of the unconscious, the term being used here in a general sense for all those mental processes of which the individual is not aware while they occur in him.

The present interest in the unconscious is a result of the advance of science and psychology since the mid-1800s, and to understand this interest requires some knowledge of the history of ideas. But the timing of this outburst of interest, its intensity (which is greatest in the English-speaking countries and least in Russia and China), and the particular conception of the unconscious that is now dominant are mainly due to one man, Sigmund Freud. His high degree of success in creating widespread appreciation of the power of the unconscious makes the improvement of his...