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Friday, November 22, 2013


Saint Thomas’s Aristotle and Actus Essendi

by Orestes J. Gonzalez





Orestes J. Gonzalez, “Saint Thomas’s Aristotle and Actus Essendi” (paper, Annual Meeting of the American Catholic Philosophical Association, Indianapolis, IN, November 1, 2013).




This paper explores how Aquinas was able to attribute to Aristotle a doctrine of creation in terms of a causa essendi of all things without attributing to him the notion of actus essendi.

It is well known that Aquinas attributed to “his Aristotle” a number of views and principles not found in the real, historical Aristotle. One important example of this “expansion” would be the notion of causa essendi.

There is also no question that Aquinas employs all the conceptual resources of his own thought when he explains the connection between the concepts of creation and actus essendi. That Aquinas attributed to his Aristotle a doctrine of creation is commonly accepted, and it is not the purpose of this article to discuss this point. In this paper I wish to focus rather on a closely related question that has remained largely unaddressed, certainly in the form in which it is presented here.

The question is this: How could Aquinas describe Aristotle’s doctrine of creation in terms of a causa essendi of all things without any reference to the actus essendi which figures so prominently in his own doctrine of creation? Aquinas directed attention towards the actus essendi of extramental subsisting things as the ultimate ground of metaphysical inquiry. 

I develop my argument in three points.

First point: Generation, corruption and creation

A first piece of the puzzle is found in Aristotle’s doctrine of the eternity of the world, which is distinct from the scriptural concept of a creation in time.

Creation—the activity of bringing something into existence out of nothing in the beginning—is radically distinct from the production of a thing by way of generation and corruption. When a thing comes into existence by way of generation and corruption the thing generated is preceded by pre-existing materials. On the other hand, the phenomenon of passing from non-being into being, with no intervention of intermediary pre-existing materials, is what most properly defines the revealed concept of creation.

Philosophers have postulated a broader notion of creation. Aquinas himself distinguishes clearly between  creation ex nihilo secundum ordinem durationis (to refer to the causation of being with a beginning in time) and creation ex nihilo secundum ordinem naturae (to refer to the causation of being ab alio, from another, regardless of whether the created reality has existed from all eternity, or not).

Now, for the Aristotle-of-Aquinas the world was eternal and generation and corruption were perpetual. In that way, for the Aristotle-of-Aquinas the world always existed with a constant uninterrupted flow of generation and corruption of things. It is through this beginningless and endless chain of accidental and substantial changes involving perishable pre-existing materials that the Aristotle-of-Aquinas explains how things come into existence in the visible world. The world of the Aristotle-of-Aquinas is presented as a beginningless eternal world.

Revelation, on the other hand, teaches that the world is not eternal. In the Christian conception of creation the world had a definite beginning. In its Christian sense, the term “creation” is used to mean both the causation of being and the definite origin in time of what is caused.

There are then two positions regarding the origin of things: one holding that things have been brought into being by God at the beginning of time; and second, the position that things have emanated from God eternally.

What the two positions essentially describe is two types of causation of being. The first type of causation of being involves the passing from non-being into being—de non esse ad esse. This is a causation which is preservative of being with a beginning in time. This means that there was nothing before the material world was brought into existence by the cause of being in the beginning.

The second type of causation involves only conservation of being. It is a causation which is preservative of being without a beginning in time. And this means that there never was a time when there was nothing in existence because the world is a beginninglessly eternal world.

In the first type of causation there are two activities: (a) the passing from non-being into being, and (b) preservation. In the second type of causation there is only one activity, preservation. It is this second type of causation that Aquinas finds suitable to explain Aristotle’s conception of the world.

Second point: The proof from motion establishes a first causa essendi

Let us now return to our discussion of Aristotle’s causa essendi.

A well-defined demarcation between the phenomenon of motion and the activity of passing from non-being into being secundum ordinem durationis makes evident that in his exposition of the proof for the existence of God based on the observation of motion, Aquinas does not intend to provide support for his doctrine of the actus essendi. In this exposition, Aquinas defines motion as the passage from potency to act. However, by way of contrast with this definition, Aquinas explains at length what his own understanding of creation ex nihilo secundum ordinem durationis is: The passage from non-being into being is not a passage from potency to act. The non-being of the thing to be produced is not potency.

In the activity of causing the being of things according to their entire substance, the starting point is nothingness. But nothingness cannot be considered to be an intermediary which at some point enters into a process of passing from potency to act.

For Aristotle, on the other hand, motion is a beginninglessly eternal activity present in a beginninglessly eternal world. In such a world, an initial activity of passing from non-being into being with no intervention of pre-existing materials is radically excluded.

Aquinas nevertheless pays serious attention to the proof from motion because it provides valid support for the truth of the existence of God as the cause of being of the world. At the same time, however, the difficulties Aquinas encounters in conceptualizing how an Unmoved Mover can be said to be the ultimate cause of being of a beginninglessly eternal world moves him to say with Saint Augustine, “This is understood only with great difficulty.” (See Summa theologiae, part I, question 46, article 2, ad 1; and De aeternitate mundi, Rome: Leonine edition, 1976, vol. 43, p. 88, lines 233-237.)

Here is what Aquinas says in his Commentary on the Eighth Book of Aristotle’s Physics: “Both here [in the Physics] and in the Metaphysics, Aristotle uses the eternity of motion to prove the first principle. This method of proving the existence of a first principle is most efficacious and irresistible. For if on the supposition that both motion and the world existed forever it is necessary to posit one first principle, then if their eternity is rejected it is all the more necessary, for it is clear that every new thing requires a principle bringing it into being. Now the only reason why it could seem that no first principle would be necessary, would be if things were ab aeterno. But if the existence of a first principle follows even on that supposition, i.e., that the world existed ab aeterno, it is clear that the existence of a first principle is absolutely necessary.” (See Commentaria in octo libros Physicorum Aristotelis, Rome: Leonine edition, 1884, vol. 2, p. 364, lines 5b-17b.)

In his effort to make sense of this position, Aquinas goes so far as to say that, although nothingness never occurs in a beginningless eternal world, nothingness is precisely the property which a thing would have of itself in such a world, because by metaphysical priority, if a thing were left to itself, it would be nothing.

Third and final point: Causa essendi need not refer to actus essendi

Aquinas did not restrict the notion of causa essendi to include only the cause of the metaphysical principle of the actus essendi

For an answer to the question "What is actus essendi?" see Chapter One of my Actus Essendi and the Habit of the First Principle in Thomas Aquinas (New York: Einsiedler Press, 2019).

The cause of the actus essendi of an extramental subsisting thing is indeed God, the Creator. The metaphysical principle of actus essendi of an extramental subsisting thing is a proper effect of God. But in a more general context, Aquinas also identified as causa essendi a number of realities which do not cause the metaphysical principle of actus essendi.

The sun, for example, is said to be the causa essendi of illuminated air. Illuminated air, however, has layers of being which do not have the sun as their causa essendi.

It is from the observation of existing things that the question of the causa essendi arises: “There must be some cause of the fact that a thing exists, for something is referred to as causatum—caused—by reason of the fact that that it has a cause of its existing, quia habet causam sui esse.” (See In II Post. analyt., lectio 7, Rome: Leonine edition, 1989, vol. 1, p. 198, lines 33-35.)

Thus, anything that in any way whatsoever exists, has a causa essendi; its existence is a caused existence.

But the attribution of existence to something does not mean that that something is an instantiation of an actus essendi. For it is clear that not everything that has the being (esse) responding to the question whether a thing exists has also the metaphysical principle of actus essendi. And yet a causa essendi is also needed to explain the esse which responds to the question whether a thing exists.

To put it another way, a good enough point of departure to reach the existence of God as the uncaused cause is the being (esse) which responds to the question whether a thing exists.

This is neatly expressed by Aquinas in the following terms: “Philosophers confess and prove that everything that in any way exists cannot exist unless it be caused by Him who supremely and most truly has being” (De aeternitate mundi, Rome: Leonine edition, 1976, vol. 43, p. 85, lines 11-13: Omne quod est quocumque modo, esse non posse, nisi sit causatum ab eo qui maxime et verissime esse habet).

Now, the use of the expression “everything that in any way exists” (omne quod est quocumque modo) gives an unmistakable indication that in this text Aquinas is not referring to actus essendi.

The conclusion is that Aquinas can attribute to Aristotle a first mover—God—who is the cause of the being of all that is, and yet not make any reference to the actus essendi.


Here is the reasoning of Aquinas in his own words: “All created causes have one common effect which is esse—being (existence)—although each one has its peculiar effect whereby they are differentiated: thus heat makes a thing calidum esse—to be hot (to exist as a hot thing)—and a builder facit domum esse—gives being to the house (gives existence to the house). Accordingly they have this in common that causant esse—that they all cause being (that they all cause existence), but they differ in that fire causat ignem (causes fire), and a builder causat domum (causes the house). There must therefore be some cause higher than all other by virtue of which they all causent esse, and whose proper effect is esse: and this cause is God” (De potentia, question 7, article 2, corpus: Omnes autem causae creatae communicant in uno effectu qui est esse, licet singulae proprios effectus habeant, in quibus distinguuntur. Calor enim facit calidum esse, et aedificator facit domum esse. Conveniunt ergo in hoc quod causant esse, sed differunt in hoc quod ignis causat ignem, et aedificator causat domum. Oportet ergo esse aliquam causam superiorem omnibus cuius virtute omnia causent esse, et eius esse sit proprius effectus. Et haec causa est Deus).

Aquinas understood the notion of causa essendi to be much wider than simply the cause of the actus essendi.