A Brief Explication of the De Ente Proof

St. Thomas Aquinas is probably most well known for his “Five Ways”, Quinquae Viae, found in the Summa Theologiae (ST I, q. 2, a. 3). However, these arguments are frequently misunderstood because they are often presented totally removed from their relation to the rest of Aquinas’s corpus, which makes them appear much weaker than they actually are. For example, Aquinas’s First Way is often displayed as being nothing more than a reiteration of Aristotle's argument for an unmoved mover in Book 8 of the physics, however this fails to capture the novelty of the First Way, and the other Five Ways in general (Physics 251a8-251b10). The actual power of these arguments comes from Aquinas’s metaphysics of esse as presented in the De ente et essentia. This power is mostly clearly observable in chapter 4 of the De ente et essentia because this is where Aquinas provides his argument for God’s existence as first cause while explicitly utilizing his metaphysics of esse.

In order to fully understand the force and demonstrative weight of Aquinas’s argument in chapter of the De ente et essentia, one needs to first understand the background debate which he is engaging, which leads him to develop his metaphysics of esse. With that background in place, one can move on to understand his metaphysics of esse, which directly leads into his argument for God’s existence as the metaphysics, rather straightforwardly, entails the existence of a first cause. Then, one can look into potential objections to his argument from a medieval perspective, but also see how these objections may not refute Aquinas’s proof. Ultimately, Aquinas’s proof should be seen as a cogent demonstration of God’s existence.

Firstly, the medieval debate surrounding the potency within angels, must be explored in order to see why Aquinas develops his metaphysics of esse in the first place. There were discussions during the medieval period over how potency exists within angels. This question arose from the fact that in Aristotelian metaphysics, matter is the principle of potency in things, but matter also confers corporeal properties on things, such as extension (Shields, “Aristotle”, 1). Angels, though, were thought to be incorporeal beings and so there were many attempts to find ways of introducing potentiality within angels as if they were incorporeal beings with no potency in them, then it becomes difficult to conceptually distinguish them from God. So, some in the Middle Ages tried “to introduce a composition of form and matter in intelligences and souls”, also known as angels, by saying that ‘incorporeal matter’ existed in angels (Aquinas, On Being and Essence, 1). Aquinas found this position to be faulty as he shows that angels are purely immaterial beings since, as intellectual substances, they have the power to understand, but since matter perverts understanding since forms are only intelligible when they are separated from matter, angels must be purely immaterial beings. 

Thus, Aquinas’s metaphysics of esse flows from his desire to find a principle of potency in angels that does not conflict with Aristotelian metaphysics. Aquinas has a very ‘thick’ view of existence in the sense that he believes that esse contains within itself all actuality (Novotny & Novák, Neo-Aristotelian Perspectives in Metaphysics, 45). That is, it contains within itself all conceptual content as essence limits esse since it “is that through which and in which a thing has esse” (Kerr, Aquinas’s Way to God, 37). To make this clearer, essence limits or constricts esse and the joining of the two results in definite conceptual content within a thing (Kerr, Aquinas’s Way to God, 37).  Now, it is true that “‘essence’ for Aquinas is thus the definitional content of the concrete substance signifying that the substance is one particular kind of thing rather than another,” but the definitional content, essence, can only be understood if it first exists, which is why it is through essence that things have esse (Kerr, Aquinas’s Way to God, 39). This is why one can view essence as a limit on esse. Esse, in itself, is conceptually infinite because it is the most fundamental principle of actuality and so must be the ground of all conceptual content in things. Moreover, things can only have their essence if they exist, which implies that esse is more fundamental than the essence of a thing. So, if esse is conceptually infinite in itself and is more fundamental than essence, which must be true since essence is only actual because of existence, and entities with finite conceptual content exist, then essence must be that which limits existence. Essence limits esse and so reduces the conceptual content of an existent thing from something conceptually infinite to something conceptually finite. It is this composition of essence and existence, which is like the relationship of potency and actuality, which renders our world filled with conceptually finite creatures (Kerr, Aquinas’s Way to God, 13). Furthermore, differences between existent things comes down to differences in the limits on their being. For example, Aquinas would say that an elephant and apple are different because, at bottom, they have different limits on their being, which means that their esses, in reality, are different.

Now that his metaphysics of esse has been explicated, it can now be clearly shown why it entails the existence of God. The medievals made a distinction between per se and per accidens causation, which is relevant to understanding how things exist under St. Thomas’s view (Knuuttila 1). A per accidens causal chain involves things that have the causality of the series in themselves (Knuuttila 1). For example, if one throws a ball, this is a per accidens causal chain as the objects in the series, the person and the ball, both have the causality of the series, in this case motion, in themselves. A per se causal chain is one where the members of the series derive their causality wholly from a fundamental member such that if there the fundamental member of the series were not present, the entire chain would lose its causality (Knuuttila 1). An example would be a hand, which moves a stick, which in turn moves a stone. If the hand were not present, or if it were to stop moving, the stick and the stone would not have the causality of the series in any way, which is illustrative of how they derive their causality wholly from the hand. Another critical element of the per se chain is that the fundamental member of the series has the causality of the series in itself. So in the example above, the hand has the causality of the series, motion, in itself.

With this framework in mind, one can understand how finite beings gain their existence: they have it wholly derivative from something which has esse in itself, which is God. There are clearly finite objects that exist as all the things which people encounter throughout their everyday lives is a finite object of some kind. So there must be an explanation of their esse, and this leads one to conclude that finite objects receive their being from something which has esse in itself. This being would not only have esse in itself, but it would simply be esse itself because it would have no limits on its being. Moreover, since esse is the most fundamental principle of actuality and so contains within it all actuality, and essence is the principle of individuation of things which enables there to be multiple instances of the same thing, then the entity which is pure esse itself must be the only thing which is esse itself. 

A potential objection to this argument would be that things can possess their esse in themselves once they receive it from another, thus undermining locating the causality of esse within a per se chain and so undermining Aquinas’s proof. In order for Aquinas to conclude that the cause of esse in finite things is something which has esse in itself he must locate it within a per se chain because otherwise it is possible that finite beings receive their esse from something else which has esse in itself, but is not pure esse. Thus, Aquinas must demonstrate that esse, as a form of causality, can only exist within a per se chain.

However, this objection fails because the nature of esse requires that finite things receive their esse wholly from without. If one locates esse, within a per accidens chain, one will see that the position entails a vicious circularity. The circularity is that in order for some essence to be actual, it must first exist, requiring that it receives its esse from without. However, if it possesses its esse in itself, then the esse will be posterior to the essence, implying that the esse relies on the essence for its actuality. However, this cannot be as the essence relies on esse for its actuality. Thus, esse can only be located within a per se chain as locating it in a per accidens chain entails a vicious circularity.

In conclusion, Aquinas presents a powerful argument for God’s existence in chapter 4 of his De ente et essentia. The force of the argument comes from his metaphysics of esse, which he developed in order to answer the question of how potency exists in angels. Perhaps the best way to try to undermine the argument is by maintaining that finite beings can possess their esses in themselves once it has been conferred on them by another, but the issue with this line of critique is that Aquinas’s metaphysics of esse precludes esse from being located within a per accidens chain since locating esse in a per accidens entails a vicious circularity. The argument found in the De ente et essentia can be seen to the form of his ‘Five Ways’ in the Summa Theologiae and should be the proof of God should be studied in order to better understand Aquinas’s understanding of God and theology more generally (Kerr, Aquinas’s Way to God, x).

Works Cited

Aquinas, St. Thomas. On Being and Essence. Translated by Armand Maurer, 2nd ed., Pontifical Institute of Mediaeval Studies, 1968.

Aquinas, St. Thomas. “Summa Theologiae.” SUMMA THEOLOGIAE: Home, www.newadvent.org/summa/

Aristotle. The Complete Works of Aristotle. Translated by Jonathan Barnes, Princeton University Press, 1995. https://sites.unimi.it/zucchi/NuoviFile/Barnes%20%20-%20Physics.pdf

Kerr, Gaven. Aquinas’s Way to God: The Proof in De Ente et Essentia. Oxford University Press, 2015.

Knuuttila, Simo. “Medieval Theories of Modality.” Stanford Encyclopedia of Philosophy, Stanford University, 15 Apr. 2021, plato.stanford.edu/entries/modality-medieval/.

Novotny, Daniel, and Lukáš Novák. Neo-Aristotelian Perspectives in Metaphysics. Routledge, Taylor & Francis Group, 2016. 

​​Shields, Christopher. “Aristotle.” Stanford Encyclopedia of Philosophy, Stanford University, 25 Aug. 2020, plato.stanford.edu/entries/aristotle/.

Glossary

Form - the principle of actuality, or intelligibility, in a thing, according to Aristotelian metaphysics (Shields, “Aristotle”, 1)

Corporeal Matter - the common understanding of matter where it is both the principle of potentiality in a thing, but also the explanation for a thing’s physicality

Esse - plainly, it is the latin for word for the verb to be, but in Aquinas’s metaphysics it is the most fundamental ground of actuality in a thing and the ground of all conceptual content in a thing; for Aquinas, it contains within itself all actuality 

Essence - in Aquinas’s metaphysics, it is “the definitional content of the concrete substance signifying that the substance is one particular kind of thing rather than another” (Kerr, Aquinas’s Way to God, 37); it can also be viewed as a limit on esse, thus limiting the actual conceptual content in a thing; an important thing to note is that Aquinas views essence not merely as form, but as the definition content arising from the whole matter-form composite (Kerr, Aquinas’s Way to God, 37)

Incorporeal Matter - a hypothetical version of matter which is the principle of potentiality in a thing, but does not grant corporeality to a thing; this was a proposed way to explain the potentiality present in angels which was advocated for by some Church fathers, like St. John of Damascus, but later maintained by the Fransiscans in the 12th and 13th centuries (ST I, q. 50, a. 1)

Matter - the principle of potentiality in a thing, according to Aristotelian metaphysics (Shields, “Aristotle”, 1)