Summa contra Gentiles2.47 Chapter XLVII. That intellectual substances are capable of willing

Now these intellectual substances must needs be capable of willing.

For there is in all things a desire for good, since the good is what all desire, as philosophers teach. This desire, in things devoid of knowledge, is called natural appetite: thus a stone desires to be below. In those which have sensitive knowledge, it is called animal appetite, which is divided into concupiscible and irascible. In those which understand, it is called intellectual or rational appetite, which is the will. Therefore intellectual substances have a will.

Again. That which is by another is reduced to that which is by itself as preceding it; wherefore according to the Philosopher (8 Phys.), things moved by another are reduced to the first self-movers: also, in syllogisms, the conclusions which are known from other things, are reduced to first principles which are self-evident. Now, in created substances, we find some which do not move themselves to act, but are moved by force of nature, for instance inanimate things, plants and dumb animals, for it is not in them to act or not to act. Therefore there must be a reduction to some first things which move themselves to action. But the first in created things are intellectual substances, as shown above. Therefore these substances move themselves to act. Now this is proper to the will, whereby a substance has the dominion of its action, because it is in it to act and not to act. Therefore created intellectual substances have a will.

Moreover. The principle of every operation is the form whereby a thing is actual, since every agent acts for as much as it is actual. Wherefore the mode of an operation consequent upon a form must be in accordance with that form. Hence a form that does not proceed from that which acts by that form, causes an operation over which the agent has no dominion: whereas if there be a form that proceeds from that which acts thereby, the agent will have dominion over the consequent operation. Now natural forms, consequent upon which are natural movements and operations, do not proceed from those things whose forms they are, but wholly from extrinsic agents, since by a natural form a thing has being in its own nature, and nothing can be cause of its own being. Wherefore things that are moved naturally do not move themselves: for a heavy body does not move itself downwards, but its generator which gave it its form. Again, in dumb animals, the forms, sensed or imagined, which result in movement, are not discovered by the dumb animals themselves, but are received by them from exterior sensibles which act on their senses, and judged of by their natural estimative faculty. Hence, though they are said after a fashion to move themselves, in so far as one part of them moves, and another is moved, yet the actual moving is not from themselves, but partly from external objects sensed, and partly from nature. For in so far as their appetite moves their members, they are said to move themselves, wherein they surpass inanimate beings and plants; and in so far as the act of their appetite is in them a necessary sequel to the forms received through their senses and the judgment of their natural estimative power, they are not the cause of their own movement. Hence they have not dominion over their own action. But the form understood, whereby the intellectual substance acts, proceeds from the intellect itself, being conceived and, after a fashion, thought out by it: as may be seen in the form of art, which the craftsman conceives and thinks out, and whereby he works. Accordingly, intellectual substances move themselves to act, as having dominion over their actions. Therefore they have a will.

Again. The active force should be proportionate to the patient, and motive power to the movable. Now in things possessed of knowledge the apprehensive power is related to the appetitive, as the motive power to the movable: since that which is apprehended by the sense, imagination, or intellect, moves the intellectual or animal appetite. But intellective apprehension is not confined to certain objects, but is of all things: wherefore the Philosopher says of the passive intellect (3 De AnimaY that it is that whereby we become all things. Hence the appetite of an intellectual substance has a habitude to all things. Now it is proper to the will to have a habitude to all things: wherefore the Philosopher says (3 Ethic.y that it is of both the possible and the impossible. Therefore intellectual substances have a will.