52. Now that we have run through the five proofs of God's existence, we turn to the objections and replies. The first objection is from the existence of evil in the world. It runs as follows:
A. If either of two contraries were infinite, the other would be totally destroyed.
B. The name “God” designates an infinite goodness.
C. Therefore if God existed, it would be impossible to discover evil in the world.
D. Evil is readily discoverable.
E. Therefore, God does not exist.
53. The objection follows from a certain idea of “infinity”. If a principle were actually infinite, then it would by definition have no limitations. But if it had a contrary, then wherever the contrary was, the principle would not be. Thus by the extent of the contrary, we could define the limits of the principle.
54. Because God signifies not just an infinite goodness, but also the supreme principle of all existing things, a defect in any creature would seem to imply a defect in God, since the existence and nature of everything is an extension of the act of God, and a defect in the effect is traceable to a defect in the cause.
55. In his reply to the first objection, Thomas cites St. Augustine, summarizing the basic answer to the problem of evil: God does not will, but only allows evil, and this because he can bring goodness out of it.
56. Thomas’s reply is very brief and only implicitly addresses the main point of the objection. The objector’s argument fails on account of a failure to recognize the kind of infinity present in God. God’s goodness is infinite not by extent but by its perfection in itself. (Saying “There is infinite goodness.” is different from saying “There is an infinite blueberry.”) Thus there is no contradiction between the infinite goodness of God and the existence of evil in things other than God.
57. However, there does seem to be a problem explaining how an infinitely good God can be the creator of a universe in which there is evil. Evil, after all, is the absence of a good due to a thing by nature. If it is God’s act which causes the universe to exist, then a perfect act should yield a perfect effect, and there should not be any evil at all.
58. Here Thomas’s reply enters. God does not will evil directly but allows it in creatures. The difference between “willing” and “allowing” occurs here, and will recur later on when Thomas discusses divine providence (q.22). What is willed proceeds directly from the agent and participates in its own act. What is allowed is known by the agent, but proceeds from the act of another. The acts of creatures are really distinct from the act of God. This point is essential. The acts of creatures participate in God’s act to the extent that they are good. To the extent that they defect from the good, they do not participate in God’s act, and are not willed by God but allowed by him. But also, to the extent that they defect from the good, they lack reality, i.e. simply speaking they are not.
59. This distinction shows how it is possible to say at the same time that there is evil, and that God is perfectly good, and that God does not will evil. But the question remains: why does God allow evil? Here Augustine enters: God allows evil so that he can bring goodness out of it. The answer is vague and inadequate, but because it attempts to search the divine will, which is inscrutable, it must remain that way. The essential thing is that God does not will evil, and that there is no contradiction between the existence of God and the defects observed in creatures.