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 regarded in its relation 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 (thus blindness is a certain evil in an animal), and by reason of a defect in a creature's action (thus lameness connotes 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 (peccatum) both in voluntary agents and in natural agents. A physician is faulty (peccat) 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 advance a generated being to its proper disposition and form; this is why monsters occur in nature.