During the first twenty years that Freud spent creating his theory, he assumed that most of the functions responsible for creating mental-thought structures were organized according to two different forms or principles of thought. He called these forms “primary process” and “secondary process”. The “secondary process” is identified with rational thinking and the ego, and it is easy to follow the changes that this concept underwent in the works of Freud that followed. The concept of “primary process”, on the other hand, disappeared from his later works with no explanation. This article traces the changes that the “primary process” underwent in Freud's thinking and examines the connection between his analytical technique and his research method. A close study of the changes that the “primary process” underwent reveals that Freud's developmental thought process included concepts whose directional changes may be termed “regressive”.