Summa contra Gentiles1.42 Chapter XLII. That God is one

Having proved the foregoing, it is manifest that there is only one God.

For it is impossible that there be two sovereign goods: since that which is ascribed to a thing by way of superabundance is to be found in one alone. Now God is the sovereign good, as we have shown. Therefore God is one.

Further. We have shown that God is absolutely perfect, and that He lacks no perfection. If, then, there be several gods, it follows that there are several suchlike perfect things. But that is impossible: for if none of them lacks any perfection, nor has any admixture of imperfection, which is required for anything to be simply perfect, there will be nothing by which they can be distinguished. Therefore it is impossible that there be several gods.

Again. That which is sufficiently done if it be supposed to be done by one, is better done by one than by many. Now the order of things is the best possible: since the potency of the first agent does not fail the potentiality of things for perfection. And all things are sufficiently perfected by referring them to one first principle. Therefore a plurality of principles is inadmissible.

Moreover. It is impossible for one continual and regular movement to proceed from several movers. For if they move together, none of them is a perfect mover, but all together take the place of one perfect mover: which does not apply to the first mover, since the perfect precedes the imperfect. If, however, they move not together, each of them is at one time moving, and at another time not; whence it follows that the movement is neither continuous nor regular: because movement that is continuous and one is from one mover. Moreover a mover that is not always 1 Ch. xli. 2 Ch. xxviii. 3 8 Phys. vi. 4.

moving is found to move irregularly: as evidenced by movers of lower degree, wherein violent movement is intense at first and slackens at the end, while natural movement is the reverse. On the other hand, the first movement is one and continuous, as was proved by the philosophers. Therefore its first mover must needs be one.

Again. Corporeal substance is directed to spiritual substance as its good: for there is in the latter a fuller goodness to which corporeal substance seeks to be likened, since whatever exists desires to attain the greatest good as far as possible. Now all movements of the corporeal creature are found to be reduced to one first movement, beside which there is no other first movement not reducible to it. Therefore beside the spiritual substance which is the end of the first movement, there is no other that cannot be reduced to it. Now under this name we understand God. Therefore there is only one God.

Moreover. The mutual order of all diverse things that are directed to each other is on account of their order towards some one thing: even as the mutual order of the parts of an army is on account of the order of the whole army to the commander-in-chief. For that certain diverse things be united together in some relationship, cannot result from their own natures as distinct from one another, because from this there would rather result distinction among them. Nor can it result from different causes of order: because these could not possibly of themselves as differing from one another have one order in view. Accordingly either the mutual order of many is accidental, or it must be reduced to one first cause of that order, who sets all in order towards the end which he intends. Now, all the parts of this world are observed to be ordered to one another, in so far as certain things are aided by certain others: thus the lower bodies are moved by the higher, and the latter by incorporeal substances, as shown above. Nor is this accidental, since it happens always or for the 1 8 Phys. vii. seqq. 2 Chs. xiii., xx.

most part. Wherefore this world has but one director and governor. But there is no other world besides this. Therefore there is but one governor of the universe, and Him we call God.

Again. If there be two things both of which are of necessity, they must needs agree in the intention of the necessity of being. It follows, therefore, that they must be differentiated by something added either to one or to both of them; and consequently that either one is composite, or both. Now no composite thing exists necessarily per se, as we have proved above. Therefore there cannot possibly be several things each of which exists necessarily: and consequently neither can there be several gods.

Moreover. That in which they differ, on the supposition that they agree in the necessity of being, is either required as a complement in some way to this necessity of being, or is not required. If not, it follows that it is accidental: because whatever is added to a thing, that has nothing to do with its being, is an accident. Therefore this accident has a cause. And this cause is either the essence of that which exists of necessity, or something else. If it is its essence, since the very necessity of being is its essence, as shown above, the necessity of being will be the cause of that accident. But necessity of being is found in both. Therefore both have that accident: and consequently are not differentiated thereby. If, thowever, the cause of this accident be something else, it follows that unless this something else exist, this accident would not exist. And without this accident there would not be the aforesaid distinction. Therefore without that something else, these two things that are supposed to exist of necessity would be not two, but one. Therefore the proper being of both is dependent on a third: and consequently neither of them exists necessarily per se.

If, on the other hand, that in which they differ be necessary as a complement to their necessity of being, this will be either because it is included in the notion of the necessity 1 Ch. xviii. 2 Ch. xxii.

of being, as animate is included in the definition of animal, or because necessity of being is specified thereby as animal is completed by rational. In the first case, it follows that wherever there is necessity of being, there is that which is included in its notion; thus to whatever we can apply animal we can apply animate. And thus, since we ascribe necessity of being to both the aforesaid, they cannot be differentiated thereby. In the second case, this is again impossible. For the difference that specifies a genus does not complete the generic idea, but the genus acquires thereby being in act: because the notion of animal is complete before the addition of rational, although animal cannot be in act except it be either rational or irrational. Now, this is impossible for two reasons. First, because the quiddity of that which has being of necessity, is its being, as we have proved above. Secondly, because thus necessary being would acquire being from something else: which is impossible. Therefore it is impossible to have several things each of which has necessary being per se.

Further. If there be two gods, this word god is predicated of both either univocally or equivocally. If equivocally, this is beside the present question: for nothing prevents any thing receiving an equivocal name, if the usual mode of speech allow. If, however, it be predicated univocally, it must be said of both in the same sense: and thus it follows that in both there is the same nature in common. Either, therefore, this nature is in both according to the same being, or else it is according to different beings. If according to one being, it follows that they are not two but only one: for two things have not one being if they differ substantially. If, however, there is a different being in both, the quiddity of neither will be its own being. But we must admit this to be the case in God, as we have proved. Therefore neither of them is what we understand by the name of God, and consequently it is impossible to admit the existence of two gods.

Again. None of the things that belong to a particular 1 Ch. xviii. 2 Ibid.

signate thing as such, can possibly belong to another: because the singularity of a particular thing belongs to no other but the singular thing itself. Now, its necessity of being belongs to that which is of necessity in as much as it is this signate thing. Therefore it cannot possibly belong to any other thing: and thus it is impossible that there be several things each of which exists of necessity. Therefore it is impossible that there be several gods.

Proof of the middle proposition: If that which is of necessity is not this signate thing as being of necessity, it follows that the designation of its being is not necessary in itself, but depends on something else. Now a thing according as it is in act is distinct from all else, and this is to be this signate thing. Therefore that which is of necessity depends on something else for being in act: and this is contrary to the notion of that which is of necessity. Therefore that which is of necessity must be of necessity according as it is this signate thing.

Again. The nature signified by this word God is individualized either by itself in this God or by something else. If by something else there must be composition therein. If by itself, it follows that it cannot be applied to another: for that which is the principle of individualization cannot be common to several. Therefore it is impossible that there be several gods.

Moreover. If there be several gods, it follows that the divine nature is not identically the same in each. Therefore there must be something to distinguish the divine nature is this one and that one. But this is impossible: since the divine nature receives no addition whether of essential or of accidental differences, as proved above nor is the divine nature the form of any matter, so as to be divided as the matter is divided. Therefore there cannot possibly be several gods.

Again. The being proper to each thing is but one. Now God is Himself His very being, as shown above. Therefore there can be but one God.

Further. A thing has being according as it has unity: wherefore every thing shuns division so far as it can, lest it thus tend to not-being. But the divine nature surpasses all in having being. Therefore there is supreme unity therein. Therefore it is nowise divided into several.

Moreover. We observe that in every genus multitude proceeds from some kind of unity: wherefore in every genus we find one first thing, which is the measure of all things found in that genus. Hence whatever things we find agreeing in one point, must proceed from some one principle. Now all things agree in the point of being. Therefore that which is the principle of all things must needs be one only: and this is God.

Again. In every government he who presides desires unity, Wherefore the chief form of government is a monarchy or kingdom. And of our many members there is one head: and this is an evident sign that unity is due to whom headship is becoming. Wherefore we must confess that God, Who is the cause of all, is simply one.

We can moreover infer this confession of the divine unity from the sacred oracles. For it is said (Deut. vi. 4): Hear, O Israel, the Lord thy God is one; and (Exod. xx. 3): Thou shalt not have strange gods before Me; and (Eph. iv. 5): One Lord, one faith, etc.

By this truth the heathens who believe in many gods are refuted. And yet several of them affirmed the existence of one supreme god, by whom they asserted that the others whom they called gods were caused, for they ascribed the godhead to all eternal substances, especially by reason of wisdom, felicity and governance of the universe. This mode of expression is found even in Holy Writ, where holy angels or men or judges are called gods, as in the words of the psalm: There is none among the gods like unto Thee, O Lord, and again: I have said: You are gods: and many like passages are found throughout Scripture. fe, Wherefore the Manichees would seem yet more opposed 1 Vulg., our. 2 ps> bcxxv. 8. 3 Ps. lxxxi. 6.

to this truth, since they assert two first principles, the one of which is not the cause of the other.

The Arians too impugned this truth by their errors, since they asserted that the Father and the Son are not one but distinct gods, and yet were compelled by the authority of Scripture to confess that the Son is true God.