Book Two — Creation, Chapter 29 — Summa Contra Gentiles
[15] On the other hand, considering the production of a particular creature, we can see a debt of justice in it by comparing a posterior creature to a prior one; and I say prior, not only in time but also in nature.
[16] Thus, in the effects to be produced first by God, we discover nothing due, whereas in the production of subsequent effects, dueness is found, yet in a different order. For, if things prior in nature are also prior in being, those which follow become due on account of those naturally prior; given the causes, the possession of actions by which to produce their effects is due them. On the other hand, if things prior in nature are posterior in being, then the prior become due on account of the posterior; for medicine to come first in order that health may follow, is something due. Both cases have this in common: the dueness or necessity is taken from that which is naturally prior in relation to that which is naturally posterior.
[17] Now, the necessity arising from that which is posterior in being, although prior in nature, is not absolute, but conditional; if this ought to come to pass, then this must precede. So, in accordance with this kind of necessity, dueness is found in the production of creatures in three ways. First, there is a conditional indebtedness on the part of the whole universe of things in relation to each part of it that is necessary for the perfection of the whole; for, if God willed the production of such an universe, it was due that He should make the sun and moon, and like things without which the universe cannot be. Secondly, something conditionally due is found in one creature in relation to another; if God willed the existence of animals and plants, then it was due that He should make the heavenly bodies by which those things are kept in being; and if He willed the existence of man, then He has to make plants and animals, and the other things which man requires for a complete existence. And yet God made both these and other things of His pure will. Thirdly, there is something conditionally due in each creature as regards its parts, properties, and accidents, upon which the creature depends either for its being or for some perfection proper to it. For example, given that God willed to make man, it was man’s due, on this supposition, that God should unite in him soul and body, and furnish him with senses, and other like aids, both intrinsic and extrinsic. Now, in all these cases, rightly considered, God is said to be a debtor, not to the creature, but to the fulfillment of His own purpose.
[18] But there is also another mode of necessity in the nature of things whereby a thing is said to be necessary absolutely; and this necessity depends on causes which are prior in being-on essential principles, for instance, and on efficient or moving causes. But this kind of necessity can have no place in the first creation of things so far as efficient causes are concerned, since in that creation the sole efficient cause was God, who alone can create, as we have already shown. But, as we have also proved, it is not by any necessity of His nature but by His will, that God works while creating; and things done by the will can have no necessity except only on the supposition of the end; for the existence of those things by which an end is attained is that end’s due. As regards formal or material causes, on the other hand, nothing prevents our finding absolute necessity even in the primal creation of things; for just because certain bodies were composed of the elements it was necessary that they be hot or cold; and from the very fact that a surface was extended in the form of a triangle it was necessary for it to have three angles equal to two right angles. But this kind of necessity results from the relation of an effect to its created material, or formal, cause, so that God cannot be said to be a debtor from the point of view of such necessity; here the debt of necessity falls upon the creature. However, in the propagation of things, where the creature is already active, an absolute necessity can arise from the created efficient cause; the sun’s motion, for example, necessarily gives rise to changes in terrestrial bodies.
[19] According to the foregoing kinds of dueness, then, natural justice is found in things, both as regards the creation of things and as regards their propagation. And so it is that God is said to have formed and to govern all things justly and reasonably.
[20] By what has been said a double error is eliminated: the error of those who, setting limits to God’s power, said that God can do only that which He does because He is bound to this; and the error of those who assert that all things follow from the sheer will of God, there being no other reason either to be sought in things, or to be assigned.
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