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Being as Being: Aristotle vs Aquinas Research Paper


The philosophical concept of being as being is concerned with the notion of existence, more specifically, that of the thing in and of itself. Regarding a person, for example, this would mean that they are not placed in a context of relationships or within the society, but their inherent person-ness. It is a crucial notion that lies at the root of metaphysics. This paper is concerned with the perspectives of St. Thomas of Aquinas and the Greek philosopher Aristotle on the concept mentioned above.

Essence and Existence according to Aquinas

In Thomistic philosophy, essence and existence are the two principles that explain the being of everything. Essence is a formal principle, an abstract concept that denotes the extent of our knowledge about a thing. For example, humanity is the essence of a human being. However, knowing what a thing is, is not enough to fully comprehend that it exists; the philosopher’s knowledge of the features and attributes of the mythical bird phoenix does not necessarily mean that it exists in reality. For Aquinas, “it is evident that the act of existing is other than essence or quiddity” (Magee 2013, par. 2). The word quiddity comes from the Latin “quid,” meaning the question “what?”

Esse and God

The activity of being, thus, is called existence, or esse, from the Latin verb “to be.” Things that exist in reality exercise their act of existence, actualizing potency just as the form actualizes the matter. Therefore, esse actualizes the potency of a thing’s essence. These two principles are distinct yet inseparable in real beings. Both of them are needed for all existing individual things, except God, to exercise their being. According to Aquinas, “intelligence is form and an act of existing, and… it has its act of existing from the First Being which is (simply) existence only; and this is the First Cause, God” (Magee 2013, par. 5).

However, humans cannot know what God is, but only what God is not, and how God is not, meaning the qualities God does not possess. For example, God is not limited, not composite and does not lack anything in any way. Therefore, Aquinas sees God as the ultimate Being, the Cause of all things, and sees humans as created in his image, and “the question of proving the existence of God is always bound up with the question of how, and to what extent, we can know God at all” (Magee 2015, par. 2). The Greek philosopher Aristotle, a student of Plato, holds reasonably different views as corresponding to his era. He proposes the existence of a single, imperishable, eternal substance, the prime mover. He argues that this is not a supreme being, but a universal intellect.

Substance and Accidents

Substance and accidents are other intrinsic principles of being as being; the concept of the primacy of substance is crucial to the study of metaphysics. Accidents, thus, can be defined as what exists in and is said of another thing, for example, a particular notion of quality, such as a color or shape. Substance, then, is what does not exist in and cannot be said of another thing, a negative criterion. A tree or a flower exist in their own right, thus “the primary substance is not predicated of anything else, whereas other things are predicated of it” (“Aristotle’s Metaphysics”). Accidents are the changes that substances undergo, though they do not directly modify the kind of a particular substance. Moreover, one cannot find an accident apart from the substance. According to Kenny’s understanding of the philosophy of Aquinas, only substances, strictly speaking, can have essences; accidents do so only in a limited sense (7).

Per the two basic meanings of substance, it is either the essence of a thing, the so-called second substance, or that thing is a subject, the first substance. Thirdly, the substance can be the universal or genus; the first substance is also known as the substrate. Cohen, elaborating on Aristotle’s notions, posits that “the dependence of secondary substances on primary substances is immediate” (235). A substance cannot be further divided, but accidents are divided into nine categories: quantity, quality, relation, action, passion, time, place, disposition, raiment. The three kinds of substance’s priority over accidents are: logical, causal and ontological. Moreover, as stated by Mitchell, Aristotle posits that physics is not the ultimate discipline in the study of beings, as “two types of substances go beyond the domain of Physics: the immobile mover of the heavens and the active intellect” (403).

Potency and Act

Potency and act are trans-categorial modes of being that are studied by metaphysics. As to the problem of movement, a being that moves is in potency, with the movement being an imperfect act while it hasn’t yet come to its end. Speaking of composition, a human soul as an act is distinct from movement, as it is not imperfect and has life in potency. Elaborating on Aristotle’s ideas, Mitchell concludes that “The matter and form of a substance are the substance itself considered respectively in potency and in act” (403). It is the moving cause that makes the substance pass from potency to act. The notions of potency and act, thus, can be used to explain the relationships between essence and existence, substance and accidents, and matter and form as concerning the metaphysical structure of reality. The distinction between act and potency can be best explained by analogy, for example, act is to potency just as somebody who is awake is to someone who is asleep, or as somebody who is running is to someone possessing the ability to run. Therefore, it is potency that limits act. The act’s priority over potency can be logical, ontological and causal as well. According to Aristotle, potency is “a fundamental meaning of being, present in all the categories” (Mitchell 403).

Matter and Form

Further on the subject of matter and form, substantial individuals are seen as compounds of the former and the latter. Matter and form, and the compounds thereof may be considered subjects. As to the question of substance, it cannot be said that the substance of a thing is the matter of which the thing is composed, being devoid of any form. A notion of prime matter is then rejected, substance must be separate and able to exist independently. Thus, the matter could exist independently of it, such as, for example, wood existing both before and after it is made to serve as furniture. However, it wouldn’t be a definite, determinate individual, but a certain quality, an aforementioned accident.

Aristotle on Essence

As to the notion of essence as a characteristic of being, Aristotle links it to the notions of definition and predication. But, as one defines things, not words, the definition of a tree, for example, would inform us of the essence of it, meaning, that it is to be a tree, not what the word “tree” means. One could see certain inconsistencies with the theory, as, if substance is form, not matter, and form is universal, but it is presumed that no universal is substance. Viewing each substance as one and the same with its essence, it is possible to infer the existence of a universal, substantial form that is that essence itself. Aristotle views substance as a principle and cause of being, distinguishing four different causes: material, formal, efficient and final.


Metaphysics as a science is directly concerned with the notion of being as being, the thing in itself and the nature of its existence. The philosophy of Aquinas elaborates on the notions of essence and existence as the two fundamental principles used to explain being. Existence actualizes the potency of the essence. Aristotle, on the other hand, views substance as one and the same with essence, and potency is a fundamental meaning of being. Substance and accidents, as other principles of being, denote what the thing is, and certain qualities it is said to have, respectively. Humanity is the essence of a person as a being in itself. Aquinas proves the existence of God as a supreme being and states that humans are created in its image, a theosophical point of view. Aristotle is concerned with the universal moving force; his notions are not based on faith, but on further developing the philosophy of Plato. He applies the laws of physics to the matter, however, finding that certain notions, such as the force above and the human intellect cannot be explained using these laws only. However, he rejects the notion of prime matter, as matter cannot constitute the substance of being.

Works Cited

Stanford Encyclopedia of Philosophy. 2015, Web.

Cohen, Marc S. “Accidental Beings in Aristotle’s Ontology.” Reason and Analysis in Ancient Greek Philosophy: Essays in Honor of David Keyt, edited by Georgios Anagnostopoulos & Fred Miller Jr, Springer Netherlands, 2013, 231-242.

Kenny, Anthony. Aquinas on Being. Clarendon Press, 2002.

Magee, Joseph M. “On Being and Essence, Ch. 4 (excerpt)”.Thomistic Philosophy Page. 2013, Web.

Magee, Joseph M. “Aquinas on God’s Existence.” Thomistic Philosophy Page. 2015, Web.

Mitchell, Jason A. “From Aristotle’s Four Causes to Aquinas’ Ultimate Causes of Being: Modern Interpretations.” Alpha Omega, vol. 16, no.3, 2014, pp. 399-414, Web.

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