This point where the soul has its seat, is, according to Descartes, not the whole brain but the pineal gland, a little kernel in the middle of the brain. The proof for this claim, that the pineal gland is the only place where the soul immediately exhibits its energy, is found in the circumstance that all other parts of the brain are twofold, which should not be in an organ where the soul has its seat, else objects would appear double. There is, therefore, no other place in the body where impressions can be so well united as in this gland. The pineal gland is, therefore, the chief seat of the soul, and the place where all our thoughts are formed. We have thus developed the fundamental thoughts of the Cartesian system, and will now recapitulate in a few words the features characteristic of its standpoint and historic position. Descartes was the founder of a new epoch in philosophy, _first_, from his postulate of universal freedom from all preconceptions. His protesting against every thing which is not posited by the thought, against taking any thing for granted in respect of the truth, has remained from that time onward the fundamental principle of the new age. _Secondly._ Descartes has brought out the principle of self-consciousness (the mind or the thinking substance is regarded by him as an individual self, a particular Ego)—a new principle, unknown in this view to the ancients. _Thirdly._ Descartes has shown the opposition between being and thought, existence and consciousness, and the mediation of this opposition, which has been the problem of the whole modern philosophy, he first affirmed as the true philosophical problem. But with these ideas, which make an epoch in the history of philosophy, there are at the same time connected the defects of the Cartesian philosophizing. _First._ Descartes gained the content of his system, namely his three substances, empirically. True, the system which begins with a protestation against all existence would seem to take nothing for granted, but to derive every thing from the thinking. But in fact this protesting is not thoroughly carried out. That which seems to be cast aside is afterwards, when the principle of certainty is gained, taken up again unchanged. And so it happens that Descartes finds at hand not only the idea of God, but his two substances as something _immediately given_. True, in order to reach them, he abstracts every thing which lies immediately before him, but in the end the two substances are seen as that which remains when all else is abstracted. They are received _empirically_. The _second_ defect is, that Descartes separates so wholly from each other the two sides of the opposition between thought and being. He posits both as “substances,” _i. e._ as powers, which reciprocally exclude and negate each other. The essence of matter according to him consists _only_ in extension, _i. e._ in the pure being _extra se_ (_Aussersichsein_), and that of mind _only_ in thought, _i.