A uniform systematic psycho-analytical theory of thinking does not as yet exist. It is possible, however, to indicate the position occupied by thinking within the framework of psychoanalytic theory. In the first part of the paper it is shown that thinking occupies, in the drive-theoretical phase of psycho-analysis, a different position from that which it holds in the present structural phase. At present, thinking is conceptualized as a function of the ego.

The process, the means (or instruments), and the product of thinking are distinguished. On the basis of clinical material two instruments of thought are described: first, the controlled temporary regression, while retaining reality testing and the synthetic function of the ego, and also the disturbances of this mechanism of thinking; second, the selective style of thought which is frequently used in, for example, mathematical thinking. An instance is given where it is used incorrectly, and the relation between the style of thought of the patient and the technique of interpretation is touched upon.