Summa contra Gentiles2.22 Chapter XXII. That God can do all things

Hence it is clear that the divine power is not determined to one particular effect.

For if it belongs to God alone to create, it follows that what things soever cannot be produced by their cause save by way of creation, must be immediately produced by Him. Now the like are all separate substances, which are not composed of matter and form, and the existence of which we will suppose for the present: and likewise all corporeal matter. These things then, being distinct from one another, are the immediate effect of the aforesaid power. Now no power that produces immediately a number of effects, otherwise than from matter, is determined to one effect. I say immediately: for, if it produced them through intermediaries, the diversity might be owing to the intermediary causes. And I say otherwise than from matter: because the same agent by the same action causes different effects according to the diversity of matter; thus the heat of fire hardens clay and melts wax. Therefore God’s power is not determined to one effect.

Again. Every perfect power extends to all those things to which its per se and proper effect can extend: thus the art of building, if perfect, extends to whatever can have the nature of a house. Now God’s power is the per se cause of being, and being is its proper effect, as stated above. Therefore it extends to all that is not incompatible with the notion of being: for if His power were confined to one effect alone, it would be the cause of a being, not as such, but as this particular being. Now the opposite of being, which is non-being, is incompatible with the notion of being. Wherefore God can do all things but those which include the notion of non-being: and such are those that imply a contradiction. It follows, therefore, that God can do whatever does not imply a contradiction.

Again. Every agent acts in so far as it is actual. Wherefore the mode of an agent’s power in acting follows its mode of actuality: for man begets man, and fire begets fire. Now God is perfect act, possessing in Himself the perfections of all things, as was proved above. Therefore His active power is perfect, and extends to all things whatsoever that are not incompatible with the notion of actuality. But these are only those which imply a contradiction. Therefore God can do all except these things.

Moreover. To every passive potentiality there corresponds an active potentiality: since potentiality is for the sake of act, as matter for the sake of form. Now a being in potentiality cannot come to be in act save by the power of something in act. Wherefore potentiality would be without purpose were there no active power of an agent that could reduce it to act: and yet nothing in the things of nature is void of purpose. Thus we find that all things that are in the potentiality of matter in things subject to generation and corruption, can be reduced to act by the active power which is in the heavenly body which is the first active force in nature. Now just as the heavenly body is the first agent in regard to lower bodies, so God is the first agent in respect of all created being. Wherefore God can do by His active power all whatsoever is in the potentiality of created being. And all that is not incompatible with created being is in the potentiality of created being, just as whatever destroys not human nature is in the potentiality of human nature. Therefore God can do all things.

Further. That some particular effect is not subject to the power of some particular agent, may be due to three things. First, because it has no affinity or likeness to the agent: for every agent produces its like in some way.

Hence the power in human seed cannot produce a brute animal or a plant, and yet it can produce a man who surpasses the things mentioned. Secondly, on account of the excellence of the effect, which surpasses the capacity of the active power: thus the active power of a body cannot produce a separate substance. Thirdly, because the effect requires a particular matter on which the agent cannot act: thus a carpenter cannot make a saw, because his art does not enable him to act on iron of which a saw is made. Now in none of these ways can any effect be withheld from the divine power. For neither on account of unlikeness in the effect can anything be impossible to Him: since everything, in so far as it has being, is like Him, as we have proved above:—nor again on account of the excellence of the effect: since it has been proved that God is above all beings in goodness and perfection:—nor again on account of a defect in matter, since He is the cause of matter, which cannot be caused except by creation. Moreover in acting He needs no matter: since He brings a thing into being without anything pre-existent. Wherefore lack of matter cannot hinder His action from producing its effect.

It remains therefore that God’s power is not confined to any particular effect, but is able to do simply all things: and this means that He is almighty.

Hence also divine Scripture teaches this as a matter of faith. For it is said (Gen. xvii. i) in the person of God: I am the Almighty God: walk before Me and he perfect: and (Job xlii. 2): I know that Thou canst do all things: and (Luke i. 37) in the person of the angel: No word shall he impossible with God.

Hereby is refuted the error of certain philosophers who asserted that only one effect was immediately produced by God, as though His power were confined to the production thereof; and that God cannot do otherwise than act according to the course of natural things, of which it is said (Job xxii. 17): {Who)... looked upon the Almighty as if He could do nothing.