Whoever duly considers the subject can know that the body does not think, because it is material, but that the soul, which is spiritual, does. The soul of man, upon the immortality of which many have written, is his spirit, for this as to everything belonging to it is immortal. This also is what thinks in the body, for it is spiritual, and what is spiritual receives what is spiritual and lives spiritually, which is to think and to will. Therefore, all rational life that appears in the body belongs to the soul, and nothing of it to the body; for the body, as said above, is material, and the material, which is the property of the body, is added to and, as it were, almost adjoined to the spirit, in order that the spirit of man may be able to live and perform uses in the natural world, all things of which are material and in themselves devoid of life. And because the material does not live but only the spiritual, it can be established that whatever lives in man is his spirit, and that the body merely serves it, just as what is instrumental serves a moving living force. An instrument is said indeed to act, to move, or to strike; but to believe that these are acts of the instrument, and not of him who acts, moves, or strikes by means of the instrument, is a fallacy.