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Theory of Substance Against Theory of Forms

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Aristotle’s Theory of Substance and It’s Refutation of Plato’s Theory of Forms

Aristotle argues in his Theory of Substance that that which we perceive can be placed into categories. In total, Aristotle argues that there are ten categories. The first category is primary ousia, or substance, which is unique in that it is independent (2a33-34) whereas all of the other categories are accidental. They modify, describe, or convey the traits and/or attributes of a thing. This theory is a rejection of Plato’s ontology as Plato argues that the form exists independently from matter. Aristotle argues instead that all things must have form and matter or lack both for neither can exist without the other. I am sympathetic to both arguments while at the same time recognize their respective flaws and limitations.

Primary ousia, also known as substance, “is that which is neither predicable of a subject nor present in a subject” (2a12-13). In other words, a primary ousia would be a particular, individual object such as a particular human being or a particular horse. For example, I, Matthew Pajor, as an individual, am the primary ousia. I, as the individual Mathew Pajor, am not predicable of any other object. Nothing can be said to be me except me. This stands in contrast to secondary ousia, also known as essence, and any other category. “Everything except primary substances is either predicable of a primary substance or present in a primary substance” (2a33-34).

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Secondary ousia, or essence, is the species and genus of a particular individual. By genus we refer to the class of which multiple sub-types belong to (1b10-19). By species we refer to the sub-types that differentiate the members of a genus (1b10-19). For example, ‘animal’ is a genus while ‘human’ is a species of that genus. The differences that distinguish one species from another within a genus is called the differentia (1b16-19). Therefore, if the particular individual substance is Matthew Pajor, the secondary ousia is that of the genus ‘animal’ and the species ‘human’. In order to understand the relation of primary ousia and secondary ousia to the other categories, we must first understand the difference between something being ‘said of’ and something being ‘said in’

For something to be ‘said of’ it means that that thing can be said of a subject (1a17-1b9). For example, man can be said of Matthew Pajor, but it can also be said of any other human being. For something to be ‘said in’ a subject, it means that that thing belongs to the subject (1a17-1b9). To be clear however, if something is ‘said in’ a subject, it is inseparable from that subject, it is not like a limb. For example, intelligence can be said in a man while man cannot be said in intelligence. Primary substances are neither said of or said in for, as mentioned, they are not predicable. Secondary ousia can said of but not said in. Things from the other categories can be both said of and said in unless they speak of a specific primary substance of which then they can be said in but not said of.

The other categories: quantity, quality, relation, place, time, position, state, action, and affection (1b25-27) modify and describe the primary and secondary ousia. The terms in these categories are combined to make statements (2a4-6). For example: Mattthew Pajor is a 6 foot 4 inches tall intelligent human being. In that statement, Matthew Pajor is the primary substance, human being is the essence, intelligent is said in the human being, and 6 foot 4 inches is the quantity of height said in Matthew Pajor. That being said, if Matthew Pajor ceased to be 6 foot 4 inches tall or ceased to be intelligent, it would not diminish the primary substance of Matthew Pajor as Matthew Pajor.

Another feature of the relationship between primary ousia and the other categories is the capability of a primary substance to admit “contrary qualities” “while remaining numerically one and the same” (4a10-12). For example, a person can be laying now and later run. Or in Aristotle’s words,

“One and the same substance, while retaining its identity, is yet capable of admitting contrary qualities. The same individual person is at one time white, at another black, at one time warm, at another cold, at one time good, at another bad” (4a17-21).

However, primary substances cannot take on contraries of essences. For example, if Matthew Pajor takes on the essence of non-human, he would cease to be Matthew Pajor. If Matthew Pajor ceases to be a human, then he ceases to be Matthew Pajor. The secondary ousia is unchangeable if the primary substance is to be preserved as the particular individual it is. The inseparability of essence from a primary substance is the foundation of the Aristotle’s rejection of Plato’s ontology.

Plato’s Theory of Forms claims that the ideal, unchanging forms of things, real being, exist in the “intelligible realm” (517b). The things that we perceive only participate in these ideal forms and only mimic the real forms. He claims this because sensible realities, like people, are constantly changing, like when people age. This idea of real being versus coming to be is explained through his Allegory of the Cave in Book VII of the Republic where he describes chained prisoner (514a) looking at a wall where shadows pass by, not being able to see that which is making the shadows (514a-c). When the chained prisoner is freed, while initially having to painfully readjust to the new reality (515e-516a), he realizes that that which he had seen while being chained was only an imitation, or shadow, of reality (516a-b). This Allegory is meant to demonstrate that the world that we perceive with our senses is only an imperfect reflection or imitation of the intelligible realm. That which we believe certain things to be are only imperfect ‘shadows’ of the forms that exist in the intelligible realm separate from substance or matter.

Aristotle rejects the idea that form and matter can be separated saying, “it would seem impossible that the substance and that of which it is the substance should exist apart” (991b1-3). Take, for example, a human being. A human being is known to have flesh, bones, and organs. How could there be a human being without flesh? Yet, this Aristotle argues, is what Plato claims by saying that the sensible world is a mere patterning of the true forms. A form, like human being, exists without flesh as form however, if it lacks flesh, can it really be called a human being? Moreover, if we were to take in to account all the things that diverge from the ideal, it stands to reason that either nothing has really mimicked the ideal form or that all things are an imperfect participation in the ideal form. But who is to say whether a given thing is imperfect or not? For example, there are many types of tables and yet how a table is designed depends on what it is used for. A kitchen table for a kitchen is the ideal table in that context while a large ornate dining room table is the ideal table for head of state dinner. Both are ideal in their context and both are tables but neither are the same. Could it be that both are divergent from the real form or is it more likely that “the Forms are practically equal to—or not fewer than—the things” (990b4-5) in terms of number? In other words, is it possible that “to each thing there answers an entity which has the same name” (990b6-7)? In which case, there is no point for the form of the substance to exist separately because all that would do is double reality (990b23-35).

“What on earth the Forms contribute to sensible things, either to those that are eternal or to those that come into being and cease to be. For they cause neither movement nor any change in them” (991a8-11).

Forms cannot originate movement, they would require some sort of substance to take on the forms or to place the form into a given thing. In order words, things that have forms, have a given form not because that form exists in some intelligible world, but because a subject consisting of matter and form fashioned another thing of substance into a given form. As Aristotle says, “of the ways in which we prove that the Forms exist, none is convincing” (990b9-10).

While I recognize both Plato’s and Aristotle’s arguments, I am more sympathetic to Aristotle’s rejection of the Theory of Forms because I find it to be more plausible. Aristotle’s Theory of substance does not require the positing of an additional realm such as the Platonic ‘Intelligible realm’. Moreover, Plato’s Theory of Forms struggles to answer how take into account substances that possess multiple forms. For example, a multipurpose tool has a knife, a can opener, and scissors. Does that multipurpose tool possess three individual forms or a single form. If it possesses a single form, then aren’t there an infinite number of forms for anything that can be combined and reconfigured with a variety of different forms? Also, if sensible beings, like humans, give rise to other sensible forms, such as the development of new tools, there would be an infinite number of forms as there have been, and continue to be, an ever increasing number of tools that are used.

On the other hand, in Aristotle’s Theory of Substance, we look at a multitude of similar particulars and find whether they have the same essence. The more similar they are, the more closely related they are in terms of genus and species. For example, a dog and a human are both animals because they share many of the same traits. Dog and human are part of the same genus. However, two humans are part of the same species because two humans share more traits in common that do a human and a dog. Aristotle’s theory of substance and his categories are, in a sense, the way we classify things and understand the world today. We take multiple similar beings, and we classify them according to their similarity. We come to know the form of humans by looking at a multitude of similar beings and seeing what commonalities they have. Not only that, we discern to see what traits each have that are intrinsically part of the being’s essence and separate them from what are changeable traits that do not deprive from the essence of the being.

That being said, we do recognize imperfection and failure in the things around us. In recognizing imperfections in the things we sense, we understand what it means for something to be perfect because we understand the concept of imperfection. Seldom do we find things that are perfect in which case, Aristotle’s theory of substance doesn’t answer how it is that we know or comprehend the concept of perfection. Plato’s theory of forms does answer that question, but it does so in a way that is unconvincing and pushes the limits of evidence. Moreover, whether something is perfect or imperfect is often subject to interpretation.

The theory of substance supports the idea that each particular individual is unique. It makes sense to the rational mind understands that a given individual is not another individual. I am not someone else. While two individuals may share common traits in vary degrees, and those traits can be categorized, Aristotle’s Theory of Substances supports the reality which is the individuality of given primary ousia which separates it from any other substance.


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