Since it is simple and spiritual, it is by nature also immortal. The same conclusion is reached through an analysis of the will, which, as we have said, is free, i.e., not determined by any cause outside itself. In the physical world everything is determined by causal necessity, and hence there is no liberty. The faculty which is not determined by causal motives declares its independence of these causes and hence is an immaterial faculty. In opposition to the voluntarism of Augustinian thought, Aquinas holds the primacy of the intellect over the will.
Reason precedes volition.
Aquinas extends this law even to God. Creation is founded upon the essence of God in so far as this essence is known by God's intellect and can be produced through the creative act. The divine will freely selects from among the possibilities in the divine essence. Thus even in God this present order of creation has been willed because it was reasonable, and not vice versa, reasonable because willed. Analogously, in man the act of understanding precedes the movement of the will.