"The good of the grace of one soul is greater than the good of the nature of the whole universe"
- St Thomas Aquinas Ia IIa, q.24, a. 3, ad 2

— A Commentary on the First Part of St Thomas' Theological Summa

by Reginald Garrigou-Lagrange, O. P.


Question 11: The Unity of God

Why does St. Thomas now treat of God's unity? It seems that he should have discussed it before God's goodness, because unity is the first property of being considered in itself, and it precedes truth and goodness. Moreover, it seems that St. Thomas had already discussed God's unity in the third question in connection with God's simplicity, because unity is the undividedness of being, and it was already shown in that question that God is the absolutely undivided and indivisible being, because He is not composed of matter and form, of essence and existence, of substance and accident, or of other parts.

In reply to this it must be said that in this eleventh question, as appears particularly from the third article, in which St. Thomas inquires whether there are one or several gods, he is concerned especially with God's unicity; but God's unicity has its foundation in the absolute indivisibility of the divine nature(1) that is, in the unity and absolute simplicity of the divine nature. Therefore, in order properly to discuss God's unicity, St. Thomas speaks also of His indivisibility or of unity in the strict sense.

St. Thomas first treated of the divine nature, having considered it quasi-metaphysically as it is in itself.(2) He now inquires whether this divine nature can be in several gods, just as one would ask whether Michaelness can be in several angels, as humanity is found in several numerically distinct human beings. It is therefore more a discussion of God's unicity, as is evident from the third article of this question; but the two preceding articles treat of unity in general, in that it is along with simplicity the foundation of unicity.

Thus there are four articles. (I) Whether one adds anything to being. (2) Whether one and many are opposed to each other (this article confirming, as it were from on high, the fourth proof for God's existence). (3) Whether there is only one God. (4) Whether God is supremely one.

To some this seems a repetition of the preceding; yet it is not, properly speaking, a repetition, but rather a case of circular contemplation,(3) which always returns to the same supreme truth (God is the self-subsisting Being), to behold the new rays emanating from it.



State of the question. The discussion is not about numerical unity, which is the principle of number and which belongs to the category of quantity, but it concerns transcendental unity, which is a property of being and which is found in every category of being, inasmuch as we speak of the unity of substance, of the unity and simplicity of quality, of the unity of action, and similarly of the other predicaments. This distinction is implied in the first objection of this article.

It must be noted that in ancient times Parmenides and Heraclitus seriously disputed this point. Parmenides affirmed the unity and unicity of being, even denying the multiplicity of beings. He proceeded along the lines of absolute realism, conceiving the universal as existing formally in the concrete, and thus he confused universal being with the divine being and said: Being cannot be diversified by itself (because being is being and nothing else); nor can it be diversified by something other than itself (because what would be other than being would be non-being, and non-being is nothing). Hence he concluded: "Being is being, non-being is non-being, and it is impossible to think of anything else." In other words, multiplicity of beings is absolutely impossible. This argument was revived by Spinoza to prove the unicity of being.(4)

St. Thomas, following the lead of Aristotle, examined this argument of Parmenides, and says of it: "In this Parmenides and his disciples were deceived, since they always referred to being as if it had one meaning and one nature, as is the case with any genus (which is diversified by extrinsic differences). But this is impossible. For being is not a genus, but is predicated (analogically) of various things and in many different senses." (5) For the modes of being are not extrinsic to being, but being is included in them. Thus quantity still is being.

But on the other hand, of ancient philosophers it was Heraclitus who denied the unity or indivisibility and identity of being; for he said that experience tells us that everything is becoming, and nothing is, and so to some extent Heraclitus identified being and non-being with becoming, which thus would be its own reason for such, as the absolute realists maintain. Thus, contrary to Parmenides, he ends in denying the real validity of the principle of contradiction or of identity, namely, "being is being, non-being is non-being," or "being is not non-being."

Thereupon Plato sought to solve the problem of unity and multiplicity by admitting the intelligible order of ideas, the highest of which is the Idea of Good, which is one, indivisible, and immutable, and also admitting the sensible order in which all things undergo a change. This was a sort of juxtaposition of the doctrines of Parmenides and Heraclitus.(6)

Finally, Aristotle with greater penetration investigated the problem of unity and multiplicity, showing that unity is a transcendental property of being, and is found in every category of being.(7) In like manner, what makes Aristotle famous is his affirmation of the indivisibility and unicity of God, of the pure Act. But he did not explain how multiplicity of beings proceeds from the one God. For his reasoning did not lead him to admit the idea of a most free creation. The Neoplatonists, however, sought to explain by necessary emanation how plurality of beings proceeds from the One Good, inasmuch as good is essentially self-diffusive. But in doing so they denied the revealed doctrine of an absolutely free creation, and contradicted themselves, because God in operating from a necessity of His nature could not produce anything finite or limited. Now St. Thomas proceeds, however, in accordance with Aristotle's doctrine, very much improving upon it.

Conclusion. One does not add any reality to being, but is only, a negation of division.

This conclusion is proved from the analysis alone of the terms, for "one means undivided being." This is evident from inductive reasoning, by considering the various categories of being: unity of substance is undivided substance, unity of quantity is undivided quantity, and the same applies to unity of quality, action, passion, relation, place, time, position. Nevertheless, one or undivided being is capable of being divided. Thus substance, which is composed of matter and form, man, who is a composite of soul and body, likewise the continuous (magnitude, movement, time), each is undivided, but indefinitely divisible.

Hence from the analysis of the terms it is clear that unity is nothing but undivided being, as Aristotle had already shown. Hence unity does not add any reality to being, but is only a negation of division.

From this we get the following corollary, one is convertible with being, Indeed what is convertible with another is that which is prediated absolutely first of it, or necessarily and immediately whether as specific difference, or as an inseparable property. But every being is one, because it is either simple or composite. But what is simple is perfectly one, because it is undivided and indivisible. But what is composite has not being while its parts are divided. Hence every being is one.

That everything guards its unity as it guards its entity, is a signl in confirmation of this truth. Thus in every living being, whether rational or irrational, in every nation whose country is in dangerl of being attacked, we find this instinct for self-preservation. Thus the Church guards her unity of faith, government, and worship, just as she guards her being.

From this it is clear that one does not add any reality to being, but is only a negation of division. Thus there is only a distinction of the mind between them. And contrary to the teaching of Parmenides, just as being is predicated not univocally but analogically of the different categories of being and of different beings, so also is one. Thus unity can be merely either analogical, or generic, or specific, or numerical. The solution of the objections confirms this doctrine.

Reply to first objection. Transcendental unity, which is found in all the categories of being, differs from unity that is the principle of number, this belonging solely to the category of quantity.Pythagoras, and Plato to some extent, as also Bannez among modern philosophers, erred in not distinguishing between these unities. Yet there is clearly a distinction between them. Thus we say of a doctrine lacking in coherence that it is one among many others, but that it lacks unity.

Does unity that is the principle of number add any reality to being? It does not add anything really distinct from being, because what is not being is nothingness; but it adds a special and limited mode of being, which is actually and implicitly contained in being, so that quantity still is being and not other than being. It is in this sense that St. Thomas says at the end of his reply to the first objection: "The one which is convertible with being does not add a reality to being; but the one which is the principle of number does add a reality to being, which belongs to the genus of quantity." In other words, although quantity is not an extrinsic differentia to being, as rationality is an extrinsic differentia to the genus of animality, yet quantity connotes a special nature which the notion of being does not connote, and which does not apply to every being. On the contrary, one which is convertible with being does not connote any other nature than being, but the transcendental mode of this nature.

Reply to second objection. In this reply several arguments are presented that serve to elucidate the fourth way of proving God's existence.

1) What is one or undivided absolutely may be divided accidentally. Thus what is one in essence and subject may have many accidents. Likewise the continuous is one absolutely or is actually undivided, but it can be divided indefinitely into still smaller parts. Thus it is one absolutely and many accidentally.

2) On the other hand, those things that are absolutely divided and many, are one accidentally. Thus those things that are many in number are one in species or in principle. Thus many men are absolutely many.

3) Therefore, since being is one absolutely, "being is divided by one absolutely and by many accidentally." This means that one and many do not refer on equal terms to being; they are not coordinated but subordinated. "For multitude itself would not be contained under being, unless it were in some way contained under one." Thus Dionysius says that "there is no kind of multitude that is not in a way one. But what are many in their parts, are one in their whole; and what are many in accidents, are one in subject; and what are many in number, are one in species; and what are many in species, are one in genus; and what are many in processions, are one in principle." (10) Similarly, what are many in genera, are one in analogous being.

4) The elucidation of the fourth way (11) follows from this, namely, that multitude, which is subordinate to one, cannot be the reason for the unity found by participation in it, the unity of similarity, for instance, either specific, generic, or analogical. Therefore, as St. Thomas says "if one of some kind is found as a common note in several objects, this must be because some one cause has brought it about in them; for it cannot be that the common note of itself belongs to each thing, since each thing is by its very nature distinct from the other, and a diversity of causes produces a diversity of effects. Since, therefore, being is found as a common note in all things, which, in all that they are, differ from one another, it must of necessity be that being is attributed to them not of themselves but from some one cause. And this seems to have been Plato's idea, whose wish was that, prior to any multitude, there should be some unity, not only in numbers, but also in the natures of things." (12) For this reason, too, it was stated in a previous article that "every composite has a cause, for things in themselves different cannot unite unless something causes them to unite." (13) Thus the unity of being is preserved, which was the wish of Parmenides; yet it is neither univocal unity nor unicity of being that is preserved, but analogous unity of beings, which are dependent on the supreme Being.

Reply to third objection. "It is not nugatory to say being is one, because one adds an idea to being." Likewise it is not nugatory or tautological to say every being is one and the same with its phenomena; for this is the principle of identity so determined that it can be called the principle of substance. Nor is it nugatory to say being is being, non-being is non-being, because by such statements it is affirmed that being is not non-being. Likewise if we say: Flesh is flesh, spirit is spirit; good is good, evil is evil. As our Lord says: "Let your speech be yea, yea: no, no." (14) This means that being is necessarily by its nature opposed to non-being, as good is to evil, as spirit to flesh. By this the identity of being is affirmed against the contentions of absolute evolutionism.

Therefore one is undivided being. Hence one and being differ only in idea, and because our first concept is of being, one is related to being as a property to the essence from which it is derived, as, for instance, incorruptibility is related to a spiritual substance.

Index Top


1. Summa theol., Ia, q.11, a.3 (first proof).

2. Cajetan's commentary may be consulted concerning this difficulty about the arrangement of the subject matter of this part of the Summa.

3. Summa theol., IIa IIae, q. 180, a.6.

4. Ethica, def. III, axioma 7, prop. 7.

5. Com. on Metaph., Bk. I, chap. 5, lect. 9.

6. Dialogues, Parmenides (on unity), Sophista (on being).

7. St. Thomas' Com. on Metaph., Bk. V, chap. 6, lect. 7 f.; also Bk. X for a fuller discussion.

8. Summa theol., Ia, q. 19, a. 4.

9. Metaph., Bk. V, chap. 6; also Bk. X.

10. De nom. div., last chapter.

11. Summa theol., Ila, q.2, a.3.

12. De potentia, q.3, a.5. See also Summa theol., la,q.44, a.1.

13. Summa theol., 1a, q.3, a. 7.

14. Matt. 5: 37.




"Let no one wear a mask, otherwise he will do ill; and if he has one, let him burn it."

St Philip Neri

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Thomas á Kempis

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