The Thomistic proof of the immateriality of human reason consists in the argument from the fact that intellection has as its object not empirical particulars but abstract universals. A standard objection against dualism plays up the problem with the causal influence of the soul on the body (psychophysical problem). The Thomistic solution depends on the hylemorphic conception of the soul as substantial form of body, i.e. on the view that the human soul is (also) that in virtue of which a human body has those essential properties which it has.