Summa contra Gentiles1.88 Chapter LXXXVIII. That in God there is free-will

It is possible to conclude from the foregoing that free-will is to be found in God.

For free-will is applied to those things that one wills not of necessity but of one's own accord: wherefore in us there is free-will in regard to our wishing to run or walk. Now God wills not of necessity things other than Himself, as we have shown above. Therefore it is fitting that God should have free-will.

Again. The divine will, in those things to which it is not determined by its nature, is inclined in a way by the intellect, as we have shown above. Now man to the exclusion of other animals is said to have free-will, because he is inclined to will by the judgment of his reason, and not by natural impulse as brute animals are. Therefore there is free-will in God.

Again. According to the Philosopher (3 Ethic.) will is of the end, but choice is of the means to the end. Wherefore since God wills Himself as end, and other things as means to the end, it follows that in regard to Himself He has will only, but in respect of other things choice. Now Choice is always an act of free-will. Therefore free-will is befitting God.

Further. Through having free-will man is said to be master of his own actions. Now this is most befitting the first agent, whose action depends on no other. Therefore God has free-will.

This may also be gathered from the very signification of the word. For the free is that which is its own cause according to the Philosopher at the beginning of the Metaphysics; and to none is this more befitting than to the first cause which is God.