The development of the meaning attaching to the personal self, the conscious being, is the subject matter of the history of psychology.

The prehistorical and primitive period represents the true infancy of the mind.

Feeling is the consciousness of the resulting conditions - of success, failure, equilibrium, compromise or balance, in this continuous rivalry of ideas.

In the first place, Descartes stands for the most explicit and uncompromising dualism between mind and matter.

Like all science, psychology is knowledge; and like science again, it is knowledge of a definite thing, the mind.

Pythagoras took the next important step by subordinating the mere matter of nature to its essential principle of form and order, identifying the latter with reason or the soul.

The dualism itself becomes a sort of presupposition or datum; its terms condition the further problem.