Often the most difficult questions to actually answer are the simplest ones to ask. We can easily answer the question, “What is a hammer?” by simply referring to the materials, the shape, and the purpose of the hammer. It gets slightly more difficult, however, when asking a question like, “What is justice?” or “What is goodness?”

An even deeper and more abstract question is, “What is thing-ness itself?” This moves beyond what qualities a person can observe in something and into the realm of essences. One can observe that red-ness is essential to a stop sign (at least nowadays), though this too is a human convention, but what about that which differentiates a substance, like a noun, from an adjective, like a relation?

Aristotle’s Categories

Aristotle provides 10 general categories to help one distinguish the essence of something: “substance, quantity, quality, relation, place, time, position, state, action, or affection.” The most important of these is the “substance,” an independent reality that can exist without any particular accident. The other categories, called accidents, are the aspects of something that can change without changing the substance itself.

While a substance does not need any specific accident to exist, the substances that we experience do contain accidents (there is one substance that contains no accident, which classical theism understands to be God).

Accidents are dependent on substances, but substances are not dependent on accidents. A triangle, for example, would be a substance, but red-ness would qualify as an accident in a substance like a red triangle. Red-ness is not essential to something being a triangle.

Primary and Secondary Substance

It would be strange to think that an individual human is an independent reality, a substance, but then say that humanity is not. Aristotle recognized that there is a clear difference between the individual and the group. We also know that there are uniting principles besides individual substances. While every individual man and woman is its own substance, they are all united under the category of humanity. While these two substances are similar – both human – they are clearly different. Aristotle distinguished these as “primary” substances, substances that exist in themselves, and “secondary” substances, substances that exist because they include other primary substances.

The importance of this distinction is that every individual person exists in themselves as an independent entity. These independent entities are also united together according to their similar natures. All men and women are united under the category of humanity, and humanity is a real substance. But because humanity carries primary substances, individual men and women, within it, it is a secondary substance. This is why we can say that not only are individual persons substances independent of accidents like color or size, but also that the thing that unites every man and woman, humanity, is a substance as well.

This is true of higher categories as well. In order for dog-ness to exist and be defined, there must be individual species of dogs. In order to know the category of something (secondary substance), one must recognize the individual (primary substance) that makes up that category.

Substance and Accident

It matters that Aristotle distinguishes between substances and accidents because of the former’s independent existence versus the latter’s dependent existence. A substance exists in itself without requiring any particular accident. For example, a triangle could exist even if there were no color red. In contrast, red-ness could not exist if there were no substances for the red-ness to exist in. Even when we think of just the color red itself, we are not actually imagining red-ness, but a red substance, like light for example.

This relates to human beings in an important way regarding how we relate to each other. How often have relationships between humans been clouded by the accidental differences between them? These accidentals, philosophically, are not essential to the substance.

No Degree in Substances

The final important distinction Aristotle makes regarding substances and accidents is that in substances there is no degree. This means that there is no amount in the essence of something. For example, a dog is not more or less dog than another, it is either a dog or not a dog. A dog can be more or less brown, more or less hairy, but these describe the accidents of a dog, not its substance.

This has implications for something like human rights. Though the concept of human rights would not be established until long after Aristotle, it relies upon the assumption that a group of humans all possess the same human nature. Therefore, they are all equally human in substance. If they share the same substance, which cannot admit degrees, then there can be no group that is more or less human.

First Principles

One of Aristotle’s most famous teachings is that the deeper questions one asks, the more important are the answers. In fact, even a small error in these foundational truths “is multiplied later a thousandfold.” One can see how a question as fundamental as “what is a thing,” or substance in itself, would have implications for our understanding of any specific substance down the line. Our actions will follow from our beliefs about reality itself, so it is important that our beliefs about reality reflect that reality accurately.

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This article was made possible by The Fred & Rheta Skelton Center for Cultural Renewal.

Image credit: Flickr-Mustang Joe, Public Domain