Commentaria in Summam contra Gentiles, Liber I

From the preceding conclusion there follows corollatively that in God nothing can be violent, and nothing outside nature. For the evidence of this, it must be considered that the violent is said to be that which comes about from an extrinsic principle, with no inclination in the patient toward it existing, indeed with an inclination toward the opposite existing. Beyond nature, however, is when in the nature there is neither inclination toward it nor repugnance. The sense of the conclusion, therefore, is that in God nothing can be that is repugnant to its nature, nor anything that is not according to the inclination of nature.

The first is proved as follows. God can have nothing added to his substance, as is clear from what precedes. Therefore nothing in him can be violent or contrary to nature. — The consequence is proved: because nothing violent or contrary to nature belongs to the substance of a thing, as is evident from the reasons of the terms.

Second. In God there is no necessity from another; rather, He Himself is the cause of necessity for others. Therefore, etc. — The consequence is proved: because necessity of compulsion is from another.

Third. Nothing can be in God except that which befits him in itself. Therefore nothing violent can be in him. — The consequence is proved. Because the violent is contrary to what is according to nature. — The antecedent, however, is evident. Because God is of himself necessary being.

Note that in that which is necessary being of itself, nothing can exist that does not belong to it necessarily, since the necessity is in it from its very substance. Therefore nothing can belong to it that does not belong to it in itself; otherwise there would be something potential in it. — This argument, however, differs from the first one. For in the first it was argued from the fact that nothing is added to its substance; in this one, from the fact that nothing can be in it besides what belongs to it in itself, whether this be substantial or not.

Fourth. God cannot be moved by another. Therefore nothing in him is violent. — The consequence is evident from the definition of the violent.

Note that this definition must be supplemented by the requirement that in the patient there be an inclination to the opposite. For it does not suffice for the account of the violent that the patient lack an inclination toward what occurs in it, for this is only beyond nature; rather an inclination to the opposite is required, because the violent is against nature.