Thomas Aquinas supports and accepts the notion of Augustine that evil is not something positive and God is not the cause of evil, because evil is not a thing. His whole answer on the problem of evil is related to God. St. Thomas Aquinas believes God did not will moral evil in any sense but only permitted it for the greater good that could not be obtained by preventing it. That is why he made man free. He also believes God did .
not will physical evil for its own sake, but he may be said to have willed it indirectly for the perfection of the universe. But why did God create this particular world where evils and suffering are present? In willing this universe, God did not will the evil contained in it, because he cannot love what is opposite to goodness, which is evil. St. Thomas Aquinas tells us that if evil were a positive entity or something created, it would be ascribed to God as a creator, but evil is not a positive thing and therefore not created, but is a privation, and exists as a privation. Therefore evil cannot be willed even by a human will. St. Thomas Aquinas says that the perfection of the universe requires the existence of various kinds of beings, such as corruptible beings, providing the possibility and not the necessity for suffering and defects. So, as evil is a privation of some particular good, it is precisely a hidden reality in things. Evil cannot be known as evil for its core is hollow, and can neither be recognized nor defined, but saved by the surrounding good. But though evil is neither good nor of God, nevertheless to understand it, it should be referred as associated with good and therefore from God.
The meaning of evil, according to St. Thomas Aquinas, depends on the meaning of good, as an opposite is known from the opposed. Thus, evil signifies an absence of good. Even in morality good and evil are different, because good in itself is our goal, while evil is the failure to seek the required goal; everybody acts for some good goal.