Chapter 111 — That the creature can fall away from its goodness

However, we must consider how there can be a lack of goodness in creatures. In two respects goodness is clearly inseparable from the creature: first, from the fact that goodness pertains to the creature’s very essence; second, from the fact that the creature is determined to one thing. As regards the first point of view, the goodness which is the form of simple substances is inseparable from them, since they are forms in essence. As regards the second point of view, such substances cannot lose the good which is existence. For form is not like matter, which is indifferent to existence and nonexistence. Rather, form follows upon existence, even though it is not existence itself.

Therefore, simple substances clearly cannot lose the good of nature wherein they subsist, but are immutably established in that good. But composite substances, which are neither their own forms nor their own existence, possess the good of nature in such a way that they can lose it. This is not true, however, of those things whose matter is not in potency to various forms or to being and non-being, such as is clear in the case of heavenly bodies.