The Universe is a Communion of Persons

We continue our exploration of the Summa contra Gentiles, in this post ending Book II.

St. Thomas’s tour of creation—at least as far as intellectual substances go—is nearly complete. The stage is nearly set for the drama of the history of the universe. The plan is as follows:

  1. an overview of the reading, ScG, II.91–101;
  2. the utrum sit question, whether the angels exist; 
  3. the being and activity question: what the angels are, and what they do; 
  4. some concluding thoughts.

8.1. Outline and some Context on Angels in ScG and Beyond

The reading might be outlined as follows:

Recall that ScG, II.90 considered the fittingness of the body to which the human intellectual soul is joined. Now, we might think of these chapters as considering the fittingness of not joining an intellectual substance to a body.

8.2. Do Angels Exist? Can We Know this Philosophically?

As Fr. Serge-Thomas Bonino, O.P. writes in his beautiful book on the angels,

Until the onset of the modern era, the real existence of the angels and demons was naively taken for granted. Angels were regarded neither as a symbolic expression of the human psyche nor as a literary device but simply and unabashedly as personal subjects, autonomous centers of existence capable of acting and routinely intervening in human history. . . . Furthermore, this spontaneous popular belief found rational confirmation in the philosophical and scientific view of the world in which angels played a decisive cosmological role.

Serge-Thomas Bonino, O.P., Angels and Demons: A Catholic Introduction, transl. by M. J. Miller (Washington, DC: The Catholic University of America Press, 2016), 71.

(See also James Collins, The Thomistic Philosophy of the Angels, Philosophical Studies 89 (Washington, D.C.: The Catholic University of America Press, 1947), for a thorough overview of the subject from a Thomistic vantage point. Fr. Bonino’s book treats the subject with greater breadth and attention to the entire swath of Catholic tradition, as well as sources in Sacred Scripture.) Now, Fr. Bonino is very much “on the side of the angels” here. Yet such philosophical innocence in the face of the wonder of the universe, however, does not impress modern scholars: “The general consensus among scholars is that these arguments [of Aquinas’s for the existence of angels] are not in fact demonstrative.” (Gregory T. Doolan, “Aquinas on the Demonstrability of the Angels,” in A Companion to Angels in Medieval Philosophy, ed. by T. Hoffmann, 35:13–44, Brill’s Companions to the Christian Tradition (Leiden/Boston: Brill, 2012), 14.) Nonetheless, some scholars are willing to grant that

inasmuch as they are not strictly demonstrations, one may also inquire what intellectual force or cogency they can be truly said to possess. Some of St. Thomas’s followers have described them as argumenta ad convenientiam—literally, arguments from convenience, whose conclusions are accepted as being in keeping with the divine purpose (or with the divine wisdom and goodness) in creating. For the Thomistic metaphysician they hold a highly persuasive value since they lead to the conclusion that angels should exist. 

First, they should exist if God’s creation is not to be without the highest reflection of himself possible in the universe he creates. 

Second, they should exist if the universe is to be complete or not lacking in any possible grade of finite being. 

Third, they should exist if the perfect in the genus of intellectual substance is to exist, a grade of beings whose actual existence would seem to hold a metaphysical priority over the existence of the human intellectual soul (a spiritual substantial form which is received into matter).

Theodore J. Kondoleon, “The Argument From Motion and the Argument for Angels: A Reply to John F. X. Knasas,” The Thomist 62, no. 2 (1998): 269–90 (, at 288–89.

Kondoleon quotes another Thomistic scholar who contends that 

The most we can say is that such separate intellectual substances are conceivable, and in view of the generally hierarchical order of the immediately experienced beings, it is convenient that angels should exist to complete the known hierarchy. Further, if they did not exist, there would be absent an important grade of being, an absence which occurs nowhere else in the hierarchy. Such a lacuna would seem to be out of harmony with the order one should expect of an infinitely intelligent Creator Who had everywhere else established an unbroken hierarchy. In a word, there should be a grade of angelic beings.

Ibid., 289–90, quoting Charles A. Hart, Thomistic Metaphysics: An Inquiry into the Act of Existing (Englewood Cliffs, NJ: Prentice-Hall, 1959), 164–65.

This is a debate that has been raging for centuries. (This is well documented and in a philosophically nuanced way in Louis-Albert Vachon, “Les Preuves naturelles de l’existence des substances séparées,” Ph.D. Diss., Université Laval, Québec, 1947.) However, other Thomistic philosophers are more sanguine about the demonstrability of the angels (among which group I count myself a student):

The inorganic world and the human species are alone part of the ultimate perfection of our cosmos. But their specific difference is not sufficiently profound to be of the essence of the universe. In corporeity they have a common natural genus. It is this insufficiency of unity of essential order that enables St. Thomas to formulate an argument for the existence of the angels who are specifically different from one another and exist outside any natural genus. Our cosmic universe is only the bottom rung of the whole of creation, of the universe in a full sense, where a pure and essential unity of order reigns. Like an isolated angelic species, our whole cosmos is only a degree, the lowest, of the universal hierarchy. It is only in the ensemble of the created universe, that is, in the ensemble constituted by all the specific universes that are the angels and the cosmos, that we find that pure hierarchy which is of the very essence of the work of God.

Charles De Koninck, The Cosmos, in The Writings of Charles De Koninck: Volume One, ed. and transl, by R. McInerny (Notre Dame, IN: University of Notre Dame Press, 2008), 320.

See also ibid., 353n120: “Our cosmos and the angels (each angel being unto itself a universe more perfect than the cosmos) constitute together the total creation, the created universe in the full sense. When we speak of the superiority of the angels we put ourselves on a uniquely natural plane. In the supernatural order it is otherwise.”

There seem to be two general strategies for proving the existence of the angels.

The principles of metaphysics and of the philosophy of nature to which this system tried to do justice have not foundered with all passengers and Freight on board, because they were not intrinsically dependent upon it, and we will find them at work again, extracted from their cosmological dross, in the two paths that open up today (perhaps) toward a philosophical affirmation of the existence of the angelic world. 

The first path, analogous to the quinque viae of proving the existence of God, would be the a posteriori way that would prove the existence of the angels starting from certain physical, psychological, or metaphysical effects that are accessible to our knowledge by going back to their cause. 

Another path, an a priori way, would start from what we know philosophically about God and his creative plan so as to deduce from it the necessary existence of a universe of purely spiritual creatures.

See Bonino, Angels and Demons, 74–75.

So, for example, the final argument in ScG, II.91 is the sort of a posteriori proof. But see also ScG, III.23 (later), and how St. Thomas evaluates this argument in II.92, especially in the opening three paragraphs. As for the a priori route, from things established prior to the consideration of angels (not in some rationalist or Kantian sense), St. Thomas’s arguments are usually in this mode; e.g., the fifth argument in ScG, II.91. The argument sketched by De Koninck in the above quote also falls under this strategy. Briefly, here is how one might characterize the proofs in ScG, II.91. (Here, I follow some of the indications by Vachon, “Les Preuves naturelles de l’existence des substances séparées,” 150ff.)

ScG, II.91Brief description, especially regarding the genus of “intellectual substances” as such
1stFrom a comparison to the separated human soul; per accidens to the per se.
2ndFrom the nature of the genus of intellectuality; the other species in this genus could be bodiless.
3rdFrom the connection of the universal hierarchy; our soul is the lowest of the higher.
4thThe imperfect implies the perfect; we are the imperfect ones in the genus, so there are others.
5thFrom the perfection of the universe (see below; also, see ST, Ia, q. 50, a. 1)
6thFrom the possibility of finding one alone w/o the other, in being
7thFrom the possibility of finding one alone w/o the other, in operation
8thFrom the need for angelic movers in the cosmos

Now, from this list, one can perhaps sympathize with those who think such proofs to be ex convenientia. Someone could easily see something of an ex pede Herculem problem here. Just because we can see part of a whole, what can we conclude about the whole with necessity? 

To assist our imaginations, perhaps we might compare Aquinas’s thinking here to an “iceberg argument”—given what we know about frozen water floating, it is physically impossible that there not be more frozen water underneath; so too, Aquinas thinks that intellectual substances are so perfect and fitting for the universe, it is impossible that there are not more above us. With this in mind, let us look more closely at the fifth argument in ScG, II.91.

Text of ScG, II.91Comments
Substance can be without quantity, although there cannot be quantity apart from substance;This begins to establish the real distinction between substance and quantity, that they can exist separately.
because substance precedes the other genera in time, nature [ratione], and knowledge.This gives the reason; note the translation change. We know that some exist prior by their ratio or nature; that is, at the very least, the separated soul.
But no corporeal substance is without quantity.Because its being is posterior to substance.
Therefore, there can be some things in the genus of substance that are altogether without a body.Note how this conclusion, from the above premises, is only to the possibility of such things.
Now all possible natures are found in the order of things: otherwise the universe would be imperfect.This is the operative premise. Were there no angels, the universe would be missing a possible gradation of being.
Moreover, in everlasting things there is no difference between actual and possible being.This is actually a quote from Aristotle, and it is reinforcing the inference from the prior conclusion.
Therefore, there are some substances subsistent apart from a body, below the first substance, which is God …, and above the soul which is united to a body.The second conclusion—the “gap” in the being of things, the hierarchy of the universe, has been filled.

8.3. What Are the Angels? What Do Angels Do?

Briefly, let us enumerate other conclusions at which St. Thomas arrives:

  1. We have already established previously that the angels are intellectual beings, and now sketches out some further consequences about what they are like.
  2. There are a great number of angels, and in this Aristotle was wrong to limit their number by some cosmological condition. See especially the argument from the order of the universe in ScG, II.92 (the third argument).
  3. The angels cannot be many in one species, because they lack matter, which is what allows for differences in number. See in particular the fourth argument in ScG, II.93, which again appeals to the principle of the perfection of the universe. (Concerning this principle, the best treatment is Oliva Blanchette, The Perfection of the Universe According to Aquinas: A Teleological Cosmology (University Park, PA: Pennsylvania State University, 1992).)
  4. The angels do not know via sensation (II.96), are always knowing (II.97), and can understand each other (II.98), but only via infused species (ideas) apart from their essences (which they can introspectively know). Such infused species are not universal concepts as we have, but universal in representative power; they permit angels to know lower substances down to the individual level. The angels can also “speak” to each other (see ST, Ia, q. 107). (John N. Deely, “The Semiosis of Angels,” The Thomist 68, no. 2 (2004): 205–58.
  5. St. Thomas treats in many other places of how angels can move to different place (by causal power), their “time” is really aeveternity, consisting of discrete moments of attention to what they know intellectually or will (see ScG, II.101). (See Juan Eduardo Carreño, “‘My Name Is Legion’: The Biblical Episode of Gerasene in the Light of Thomas Aquinas’s Theory of Angelic Location.” The Thomist 84, no. 2 (2020): 233–61 (
  6. The sin of the angels is a topic for higher studies. (See Tobias Hoffmann, “Aquinas and Intellectual Determinism: The Test Case of Angelic Sin.” Archiv Für Geschichte Der Philosophie 89, no. 2 (2007): 122–56 (

8.4 Some Concluding Thoughts

Our study of St. Thomas Aquinas’s Summa contra Gentiles has reached its halfway point. We should renew our focus by

  1. reviewing the purpose of the work and the division and order of its parts;
  2. recall some of the limits of philosophy which we encountered in Book II.

1. The Protreptic of Christian Wisdom

What are the goals of the Summa contra Gentiles?

  • To manifest the truth of the Catholic faith and to refute the opposing errors
  • To accomplish the above in a certain manner, i.e., by using philosophical arguments at the service of theological ends: “With the intention, then, of proceeding in the manner laid down, we shall first endeavor to declare that truth which is the object of faith’s confession and of reason’s researches, by adducing arguments both demonstrative and probable, some of which we have gathered from the writings of the philosophers and of holy men, so as to thereby confirm the truth and convince our opponents.” (ScG, I.9)
  • To consider topics related to such an end: “Seeing, then, that we intend by the way of reason to pursue those things about God which human reason is able to investigate, the first object that offers itself to our consideration consists in those things which pertain to God in himself [Book I]; the second will be the procession of creatures from him [Book II]; and the third the relation of creatures to him as their end [Book III].” (Ibid.)
  • To accomplish this end in such a manner as to serve as a protreptic to and training in Christian wisdom; hence the stylistic approach, providing an array of arguments both demonstrative and probable.

We are entering into Book III, concerning the relation of creatures to God as their end. This is still within the more overtly philosophical portion of the book, but philosophy has its limits when we approach these subjects from the “top-down” perspective. Let us recall some from Book II.

2. Pushing Philosophy to Its Rational Limits

  • The first major topic which we encountered was the dispute of about eternity versus the temporal finitude of the world.
  • Another topic in which we ran up against the limits of the philosophically demonstrable was the moment of the beginning of human life.
  • Again, the nature of the post-mortem soul and especially the resurrection of the body reached the limits of philosophical argument (see below).
  • Lastly, the existence of the angels was demonstrated with (at least) probable certainty. (Perhaps some greater certainty can be gained by the wise.)

Let us consider the last point.

The Philosopher and the Angels

Why might it be the case that arguments ex convenientia, or from fittingness, are of a greater strength in metaphysics than in other subjects? Here we might recall two ideas from Aristotle:

  1. “Our discussion will be adequate if it has as much clearness as the subject-matter admits of; for precision is not to be sought for alike in all discussions, any more than in all the products of the crafts.” (Nicomachean Ethics, I.3, 1094b13–14)
  2. “Perhaps, as difficulties are of two kinds, the cause of the present difficulty is not in the facts but in us. For as the eyes of bats are to the blaze of day, so is the reason in our soul to the things which are by nature most evident of all.” (Metaphysics, II.1, 993b9–12)

If it is true that “he who has not meditated on the angels will never be a perfect metaphysician,” (Jacques Maritain, Degrees of Knowledge, 221, quoted in Deely, “The Semiosis of Angels,” 258n105.) then it is also true that the perfect metaphysician is the one who has attained the acme of human certitude about the separate substances. I hope out hope for our nocturnal minds in this case.

However, for our goals in reading and studying the Summa contra Gentiles, especially as we enter the third book, we should recall that knowing about the angels, along with human beings and our beginnings and endings wrapped in a bit of philosophical mystery and possible supernatural intervention defines the dramatic narrative context of the universe, not just its ontological hierarchical dynamic. Book III will find the philosopher trying to penetrate to the true meaning of world history, the workings of providence, pushing conceptual analysis and causal argumentation to the limit, trying to see in the structure of created being the goal for which it was made.

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