Book Three — Providence, Chapter 129 — Summa Contra Gentiles
[1] From the foregoing it is apparent that things prescribed by divine law are right, not only because they are put forth by law, but also because they are in accord with nature.
[2] Indeed, as a result of the precepts of divine law, man’s mind is subordinated to God, and all other things that are in man’s power are ordered under reason. Now, the natural order requires that lower things be subject to higher things. Therefore, the things prescribed by divine law are naturally right in themselves.
[3] Again, men receive from divine providence a natural capacity for rational judgment, as a principle for their proper operations. Now, natural principles are ordered to natural results. So, there are certain operations that are naturally suitable for man, and they are right in themselves, not merely because they are prescribed by law.
[4] Besides, there must be definite kinds of operations which are appropriate to a definite nature, whenever things have such a definite nature. In fact, the operation appropriate to a given being is a consequent of that nature. Now, it is obvious that there is a determinate kind of nature for man. Therefore, there must be some operations that are in themselves appropriate for man.
[5] Moreover, whenever a certain thing is natural to any being, that without which this certain thing cannot be possessed must also be natural, “for nature is not defective in regard to necessary things.” But it is natural for man to be a social animal, and this is shown by the fact that one man alone does not suffice for all the things necessary to human life. So, the things without which human society cannot be maintained are naturally appropriate to man. Examples of such things are: to preserve for each man what is his own and to refrain from injuries. Therefore, there are some things among human acts that are naturally right.
[6] Furthermore, we showed above that man has this natural endowment, he may use lower things for the needs of his life. Now, there is a definite measure according to which the use of the aforesaid things is proper to human life, and if this measure is set aside the result is harmful to man, as is evident in the immoderate eating of food. Therefore, there are some human acts that are naturally fitting and others that are naturally unfitting.
[7] Again, according to the natural order, the body of man is for the sake of his soul and the lower powers of the soul are for the sake of reason, just as in other things matter is for the sake of form and instruments are for the sake of the principal agent. But, because of one thing being ordered to another, it ought to furnish help to that other, and not offer it any hindrance. So, it is naturally right for the body and the lower powers of the soul to be so managed by man that thereby his activity of reason, and his good, are least hindered and are, instead, helped. But, if it happens otherwise, the result will naturally be sinful. Therefore, drinking bouts and feastings, and inordinate sexual activities through which rational activity is hindered, and domination by the passions which do not permit free judgment of reason—these are naturally evil things.
[8] Besides, those acts by which he inclines toward his natural end are naturally appropriate to an agent, but those that have the contrary effect are naturally inappropriate to the agent. Now, we showed above that man is naturally ordered to God as his end. Therefore, the things by which man is brought to the knowledge and love of God are naturally right, but whatever things have the contrary effect are naturally evil for man.
[9] Therefore, it is clear that good and evil in human activities are based not only on the prescription of law, but also on the natural order.
[10] Hence it is said in the Psalm (18:10): “the judgments of the Lord are true, justified in themselves.”
[11] By this conclusion we set aside the position of those who say that things are just and right only because they are prescribed by law.
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