Chapter 112 — How creatures may fall away from goodness in their activities

But a creature’s goodness is not only considered inasmuch as it subsists in its nature, but the perfection of its goodness is found in its ordering toward the end. And since creatures are ordered toward their end by their activity, we have still to inquire how creatures may be lacking in goodness from the point of view of their actions, whereby they are oriented toward their end.

In this connection we should first note that a judgment concerning natural operations is equivalent to a judgment concerning the nature which is the principle of these operations. Therefore, in beings whose nature cannot suffer defect, no defect in natural operations can arise; but in beings whose nature can admit of defect, a defect in activity can occur.

Hence in incorruptible substances, whether non-bodily or bodily, no defect in natural activity can take place. Thus angels forever retain their natural power of exercising their proper activity. Likewise, the movements of heavenly bodies are found never to leave their appointed orbits. But in lower bodies many defects in natural activity result from the corruptions and defects incidental to their natures. Thus from a defect in some natural principle come the sterility of plants, monstrosities in the generation of animals, and other such disorders.