At the turn of the twentieth century Sigmund Freud's theories about the workings of the unconscious mind began a revolution in the way mental-health workers treated their patients. The concept of the unconscious was not new, but earlier theorists tended to see it as subordinate to conscious mental processes. For example, Freud's slightly older American contemporary William James described the unconscious as a "fringe" around the edges of conscious thought. For Freud, however, the unconscious was like the underwater part of an iceberg while the conscious was like the much smaller tip that extends above water. The unconscious, Freud said, is the realm of powerful, primitive, often sexual impulses that are frequently contrary to the morals and mores of the individual and society. In addition, he said that the unconscious is the place to which the individual banishes painful mental conflicts...