But the repressed flows together with the id, and it is only one piece of it. The repressed is strictly separated from the ego through its resistances but can communicate with the ego through the id. We immediately recognize that all the specific situations we have described so far, driven by pathology, are only related to the superficial level - the only one we know - of the mental apparatus.

From these relationships, we could form a diagram, the lines of which serve merely as a representation and do not claim any specific interpretation. It is easy to see that the ego is a piece of the id that has been altered by the direct influence of the external world through the mediation of the system of Perception - Consciousness; in a sense, it is an extension of the differentiation of the surface.

It also ensures the enforcement of the influence of the external world on the id and its drives and attempts to replace the pleasure principle, which controls the id without any restrictions, with the reality principle. Perception plays for the ego the role that drive plays for the id. The ego represents what can be called logic and prudence, in contrast to the id, which contains the passions. All the above align with well-known and accepted distinctions, but to understand it correctly, we must see it as an average or as an ideal image.

[Excerpt from the text on the back cover of the edition]