Descartes places great stress on the distinction in defining the soul as thinking being, and matter as extended being. Their fundamental attributes are so different that they must be called two different substances, and moreover in the full sense of the word, since it must be possible for the one to exist without the other. But, in that case, their interaction becomes an impossibility; for Substance, strictly speaking, cannot be acted on from without.
In his special psychology (particularly in his interesting treatise on the emotions, published in his Traité des passions, 1649) he endeavors—in harmony with his dualistic theory—to furnish a separate definition for the mental phenomena which have a psycho-physical basis from those which are purely psychical. Hence he makes a distinction between sensation and judgment, sensory and mental recollection, imagination and intellection, desire and will, affections (passions) and emotions (émotions intéreures). His precision at this point is rarely equalled even by spiritualists.
Descartes’ ethics bears an interesting relation to his world theory. He elaborated the details of this phase of his theory in his correspondence with Princess Elizabeth Christina of Sweden, and Chanut the French ambassador to Sweden.—He emphasizes the cultivation of the subjective emotions, rather than the “passions” which depend on external influences. But improvement in knowledge is likewise of great value: we discover that everything depends on a Perfect Being; we find that we are but infinitesimal parts of an infinite world, which cannot have been created on our account. We finally come to regard ourselves as parts of a human society (Family, State), whose interests take precedence over our private interests. It is important above all else to distinguish between what