A hint of the calculus and a reminder all acts intend a definite good, even when the act results in an evil.
1 It is evident from the foregoing explanation that, no matter how much evil be multiplied, it can never destroy the good wholly.
2 In fact, there must always continue to be a subject for evil, if evil is to endure. Of course, the subject of evil is the good, and so the good will always endure.
3 Yet, because it is possible for evil to increase without limit, and because good is always decreased as evil increases, it appears that the good may be infinitely decreased by evil. Now, the good that can be decreased by evil must be finite, for the infinite good does not admit of evil, as we showed in Book One . So, it seems that eventually the good would be wholly destroyed by evil, for, if something be subtracted an infinite number of times from a finite thing, the latter must be destroyed eventually by the subtraction.
Notes Be careful, here. St Thomas is not espousing some sort of cosmic battle between equals of good and evil. See paragraph . As we noticed a few times before, the next paragraph shows Aquinas understood the mathematics of the continuum! I broke up the paragraph to highlight this.
4 Now, it cannot be answered, as some people say, that if the subsequent subtraction be made in the same proportion as the preceding one, going on to infinity, it is not possible to destroy the good, as happens in the division of a continuum.
For, if you subtract half of a line two cubits long, and then half of the remainder, and if you go on in this way to infinity, something will always remain to be divided.
But, in this process of division, that which is subtracted later must always be quantitatively diminished. In fact, the half of the whole is quantitatively greater than half of the half, though the same proportion continues.
This, however, cannot in any sense happen in the decreasing of good by evil, for the more the good would be decreased by evil the weaker would it become, and so, more open to diminution by subsequent evil. On the contrary, the later evil could be equal to, or greater than, the earlier evil; hence a proportionately smaller quantity of good would not always be subtracted by evil from the good in subsequent cases.
5 So, another sort of answer must be given. It is evident from what has been said that evil does take away completely the good which is its contrary, as blindness does with sight. Yet there must remain the good which is the subject of evil. This, in fact, inasmuch as it is a subject, has the essential character of goodness, in the sense that it is in potency to the act of goodness which is lacking due to the evil. So, the less it is in potency to this good, the less will it be a good.
Now, a subject becomes less potential to a form, not simply by the subtraction of any of its parts, nor by the fact that any part of the potency is subtracted, but by the fact that the potency is impeded by a contrary act from being able to proceed to he actuality of the form.
For example, a subject is less potential in regard to cold to the extent that heat is increased in it. Therefore, the good is diminished by evil more as a result of the addition of its contrary than by the subtraction of some of its goodness. This is also in agreement with the things that have been said about evil.
Indeed, we said that evil occurs apart from the intention of the agent, and that he always intends a definite good, and that it consequently implies the exclusion of another good which is contrary to it. So, the more this intended good (which apart from the agent’s intention results in evil) is multiplied, the more is the potency to the contrary good diminished. And this is rather the way in which the good is said to be diminished by evil.
6 Now, in the natural order, this diminution of the good by evil cannot proceed to infinity. All natural forms and powers are limited, and they reach some limit beyond which they cannot extend. So, it is not possible for any contrary form, or any power of a contrary agent, to be increased to infinity, in such a way that the result would be an infinite diminution of good by evil.
7 However, in the moral order, this diminution can proceed to infinity. For the intellect and the will have no limits to their acts. The intellect is able to go on to infinity in its act of understanding; this is why the mathematical species of numbers and figures are called infinite.
Likewise, the will proceeds to infinity in its act of willing: a man who wills to commit a theft can will again to commit it, and so on to infinity. Indeed, the more the will tends toward unworthy ends, the greater is its difficulty in returning to a proper and worthy end. This is evident in he case of people in whom vicious habits have developed already, as a result of their growing accustomed to sinning. Therefore, the good of natural aptitude can be infinitely decreased by moral evil. Yet, it will never be wholly destroyed; rather, it will always accompany the nature that endures.
Notes Such a rich paragraph! First we have the notion that our knowledge of universals implies an experience of the infinite, and, as such, though Aquinas does not make the argument here, means we can only learn universals with the assistance of God. Then we have the hard truth of how hard it is to escape evil habits. Reflect on both of these.