Between the nineteenth and twentieth centuries, the subject of psychology went through a revolutionary change. The subject changed from one comprehensive topic to two separate entities. The old style of thinking is called descriptive psychiatry. In the past, descriptive psychiatry was widely used but not very deep or affective. One example of this is a mental patient's evaluation. The examining physicians continued to describe his condition with different combinations of the words stupid, dull, and demented. He was diagnosed with the same three words yearly for twenty years until he died suddenly. .
Interpretative psychiatry was a great breakthrough in the science. George H. Kirby first used this term in the introduction to the English edition of Bleluer's Textbook of Psychiatry. In this important passage, he sets the tone for the time with this quote. "This book marks a notable advance in psychiatry in that it emphasizes sharply the contrast between the older descriptive psychiatry of Krapelin and the new interpretive psychiatry of the present time which utilizes the psychoanalytic principles and general biological viewpoints developed by Freud and his pupils in Europe." This basically shows a changing of the guard in psychological techniques. Freud was now and still is the man of the hour. .
Sigmund Freud (1856-38) was the father of this new movement. His notion of the psyche evolved throughout the course of his career. Freud's three models of the psyche share the general theme that the individual's desires conflict with and are repressed by the need to conform to the expectations of the society. In the dynamic model, Freud focuses on the conflict between dynamic reality, the conscious, and the instinctual drives of the individual, represented in the unconscious. The economic model describes the difference between the pleasure principle and the reality principle. The pleasure principal s the individual bodily drive for pleasure, which must be constrained by the reality principle, which is the practical concerns of society.