Summa contra Gentiles3.4 Chapter IV. That evil is unintentional in things

It follows from the above that evil is incidental to things beside the intention of an agent.

For when the result of an action differs from the intention of the agent, it is clear that such result occurs unintentionally. Now evil differs from good which every agent intends. Therefore evil happens beside the intention.

Also. Defect in effect and action results from defect in the principle of action: thus a monstrosity results from a defect in the seed, and limping results from a curvature of the leg. Now an agent acts according as it is possessed of active force, and not according as it suffers from defective power. Andaccording asit acts,itintendstheend. Where- fore it intends an end corresponding to its power. Hence whatever follows corresponding to the defective power, will be beside the agent’s intention. And this is evil. Therefore evil occurs beside the intention.

Again. The movement of the thing moved has the same tendency as the motion of the mover. Now the thing moved tends per se to good, but to evil it tends accidentally and unintentionally. This is most evident in generation and corruption. For matter, while it underlies one form, is in potentiality to another form, and to the privation of the form which it has already: thus when it is under the form of air, it is in potentiality to the form of fire and the privation of the form of air. And the transformation of matter terminates in both at the same time: in the form of fire by reason of fire being generated, and in the privation of the form of air, by reason of the air being corrupted. But the intention and appetite of matter is not towards the privation, but towards the form: for it does not tend towards the impossible; and it is impossible for matter to be alone under a privation, whereas it is possible for it to be under a form. Therefore it is unintentional that it terminate in privation: and it terminates therein in so far as it attains the form which it intends, the necessary result whereof is the privation of the other form. Therefore in generation and corruption the transformation of matter is directed per se to the form, and privation results unintentionally. And the same must needs apply to all manner of movement: so that inevery—movement there is generation and corruption in some respect: for instance, when a thing is changed from white to black, a white thing is corrupted and a black one is made. Now the good is according as matter is perfected by the form, and potentiality by its proper act: while evil is according as it is deprived of its proper act. Consequently, whatever is moved intends in its movement, to attain some good; and it attains evil beside itsintention. Hence, since every agent and mover tends to the good, evil occurs beside the intention of the agent.

Moreover. In those things that act by intelligence or any kind of instinct, intention follows apprehension; because the intention is towards that which is apprehended as an end. Accordingly if something is attained that has no species in the apprehension, it will be beside the intention: for instance, if one were to intend to eat honey, and were to eat gall thinking that it was honey, this will be beside the intention. But every intellectual agent tends to something in so far as he considers it under the aspect of good, as we have “shown above.! Wherefore if this be not a good but an evil, it will be beside the intention. Therefore that which acts by intelligence does not work evil except unintentionally. Therefore, since to tend to a good is common to intellectual and natural agents, evil does not ensue from the intention of an agent except beside that intention. In this sense