Book Three — Providence, Chapter 13 — Summa Contra Gentiles
[1] From what has been said above it can be shown that, though evil has no direct cause of itself, still there must be an accidental cause for every evil.
[2] Whatever exists in another thing as in its subject must have some cause, for it is caused either by the principles of the subject or by some extrinsic cause. Now, evil is in the good as in a subject, as has been indicated, and so it is necessary for evil to have a cause.
[3] Again, that which is in potency to either of two contraries is not advanced to actuality under one of them unless through some cause, for no potency makes itself be in act. Now, evil is a privation of something that is natural to a man, and which he ought to have. This is why anything whatever is called evil. So, evil is present in a subject that is in potency to evil and to its contrary. Therefore, it is necessary for evil to have some cause.
[4] Besides, whatever is present in something and is not due to it from its nature comes to it from some other cause, for all things present in existing beings as natural components remain there unless something else prevents them. Thus, a stone is not moved upward unless by something else that impels it, nor is water heated unless by some heating agent. Now, evil is always present as something foreign to the nature of that in which it is, since it is a privation of what a thing has from its natural origin, and ouaht to have. Therefore evil must alwavs have some cause, either directly of itself, or accidentally.
[5] Moreover, every evil is the consequence of a good, as corruption is the result of an act of generation. But every good has a cause, other than the first good in which there is no evil, as has been shown in Book One [39]. Therefore, every evil has a cause, in regard to which it is an accidental result.
← III.12. That Evil Does not Wholly Destroy Good · Book Three — Providence Contents · III.14. That Evil is an Accidental Cause →