Chapter 119 — Of the two kinds of evil

Since evil is privation and defect, and since defect, as is clear from what we said above, can occur in a thing both as regarded in its nature and as it is ordered to an end by its action, we may speak of evil in both senses: that is, by reason of a defect in the thing itself (as blindness is a certain evil in an animal), and by reason of a defect in a creature’s action (as limping is an action with a defect). Evil in an action that is directed to an end in such a way that it is not rightly related to the end is called fault both in voluntary agents and in natural agents. A physician is faulty in his action when he does not proceed in such a way as to procure health. Nature, too, is faulty in its activity when it fails to generate a thing with its proper disposition and form; this is why monsters occur in nature.