The Puzzle of Everything: Aristotle's Quest to Sort Reality

Here’s a strange thing philosophers have noticed: when you point at something—a dog, a tree, a rock, your friend’s face—you can describe it in many different ways. The dog is brown. The dog is sleeping. The dog is next to the tree. The dog is three feet long. But here’s the puzzle: are all these descriptions pointing to the same kind of thing? Is “brown” the same kind of feature of the world as “three feet long”? Or are they fundamentally different?

Aristotle, a Greek philosopher who lived about 2,400 years ago, was one of the first people to try to answer this question systematically. He noticed that when we talk about anything in the world, we seem to be talking about it in a limited number of basic ways. He thought he could list them—and that this list would tell us something deep about what the world is actually made of.

The Two Sorts of “Is”

Let’s start with a simple sentence: “Socrates is a human.” Now consider another: “Socrates is pale.”

Grammatically, these look the same. Both have a subject (“Socrates”) and a predicate (“is a human,” “is pale”). But Aristotle thought they were doing two very different jobs.

When you say “Socrates is a human,” you’re saying what Socrates is, in his very nature. Being human isn’t something that happens to Socrates; it’s what he is. But when you say “Socrates is pale,” you’re saying something that could change. Socrates could get a tan. He could get sick and turn yellow. The paleness is, as philosophers say, accidental—it happens to be true of Socrates right now, but it’s not part of his essence.

This might seem like a small point, but it’s actually the beginning of a whole way of thinking about reality. Aristotle thought that the most basic entities in the world are things like Socrates: particular beings that aren’t properties of anything else. He called these primary substances. A particular human. A particular horse. A particular tree. These are the bedrock of reality, according to Aristotle. Everything else—all the qualities, quantities, relations—depends on them.

Think about it this way: can there be “pale” without anything that is pale? Can there be “three feet long” without anything that is three feet long? Aristotle didn’t think so. Primary substances are the anchors that hold the rest of reality in place. If they didn’t exist, nothing else would either.

The Four Ways Things Can Be

But here’s where it gets more interesting. Aristotle realized that things can relate to each other in two different ways. He used two technical terms that are worth understanding.

First, something can be said of something else. “Human” is said of Socrates—Socrates is a human. “Animal” is said of Socrates too, since humans are animals. These are the general categories that particular things fall under.

Second, something can be present in something else. The paleness of Socrates is present in Socrates—it’s a property that belongs to him. It can’t exist without Socrates. Socrates’ height is present in Socrates. The knowledge in Socrates’ mind is present in Socrates.

If you put these two ideas together—said-of or not said-of, present-in or not present-in—you get four kinds of things:

Not said-of and not present-in: These are primary substances. Socrates himself. A particular horse. They’re not properties of anything else, and they’re not general categories. They’re individual things.

Not said-of but present-in: These are particular properties. The specific paleness that Socrates has right now. The specific warmth of your cup of hot chocolate. These are what some philosophers call “tropes”—individual property-instances that can’t exist without the things they belong to. Your cup’s warmth isn’t the same thing as my cup’s warmth, even if they’re exactly the same temperature.

Said-of but not present-in: These are general categories that tell us what something is—the species and genera that primary substances belong to. “Human” is said of Socrates. “Animal” is said of Socrates. These aren’t properties that inhere in Socrates; they’re what Socrates is.

Said-of and present-in: These are general properties—universals like “pale” or “knowledge.” They can be said of many different things (many things can be pale), and they’re present in the things that have them.

This four-fold division is Aristotle’s first big idea about how to sort reality. But it’s not the only one.

The Ten Categories

Aristotle also came up with a different way of sorting things—one that became much more famous. He claimed that everything we can say about anything falls into exactly ten basic types. He called these categories (from the Greek word for “predicate”).

Here they are:

Substance (like “human” or “horse”)
Quantity (like “three feet long”)
Quality (like “pale” or “wise”)
Relation (like “larger than” or “father of”)
Place (like “in the Lyceum”)
Time (like “yesterday” or “at noon”)
Position (like “sitting” or “standing”)
Having (like “wearing shoes”)
Acting (like “cutting”)
Being acted upon (like “being cut”)

Now, you might think some of these look a bit odd. “Having” a category for “wearing shoes”? That seems awfully specific. And some of them seem like they might be the same kind of thing. Why is “sitting” different from “being in the Lyceum”? Why are “acting” and “being acted upon” two different categories instead of one?

Philosophers have been arguing about this for over two thousand years. Some have thought Aristotle’s list is brilliant. Others have thought it’s a bit of a mess. But the basic idea—that there are fundamental kinds of things that can be said about reality—has been incredibly influential.

What’s Really Real?

Here’s where we need to be careful, because there’s a serious debate about what Aristotle was actually doing. Was he classifying words? Was he classifying concepts in our minds? Or was he classifying the actual structure of reality itself?

This matters because if he was just classifying words, then his list might tell us more about the Greek language than about the universe. Maybe another language would carve things up differently. Maybe some of Aristotle’s categories don’t exist in other languages. (Think about how English has the word “the” but some languages don’t—would a philosopher who spoke only those languages miss something important about reality?)

Most scholars think Aristotle was trying to do something in between. He was classifying the ways we talk about things, but he thought this classification reflected the actual structure of the world. The categories aren’t just about language—they’re about how reality is put together.

But here’s the problem: how do you know you’ve got the right list? How do you know there are exactly ten categories and not twelve or five? Aristotle never really explained how he came up with his list. He just presented it.

The German philosopher Immanuel Kant, about 2,000 years later, criticized Aristotle for this. He said Aristotle “merely picked them up as they came his way” instead of having a systematic method. Kant tried to do better, deriving his own list of categories from the structure of logic itself. But whether he succeeded is another debate.

Why Categories Matter

You might be thinking: “Okay, so there are ten categories. So what? Why should I care?”

Here’s why this matters—and it’s a genuinely deep point. If you think the world has a certain basic structure, that affects everything else you think. It affects what you think science should study. It affects what you think exists and doesn’t exist. It affects how you understand change, identity, and causation.

Aristotle’s claim that primary substances are the most real things was a deliberate rejection of his teacher Plato’s philosophy. Plato thought that the most real things were abstract, perfect forms—like the Form of Beauty or the Form of Justice—and that particular things like Socrates were just pale copies. Aristotle said: no. The particular things are the most real. The abstract categories are real too, but they depend on the particular things.

This is still a live debate today. There are philosophers who think the most fundamental things in the universe are particles and fields (like modern physics says). There are philosophers who think the most fundamental things are experiences or minds. And there are philosophers who think the most fundamental things are exactly the kind of middle-sized objects Aristotle talked about—tables, chairs, people, dogs.

The categories framework gives you a way to ask: what do I think the basic kinds of things are? And why?

The Trouble with Categories

If you’ve been paying close attention, you might have noticed something weird. Aristotle says that “body” is a species in the category of substance (bodies are a kind of substance). But he also lists “body” as a species in the category of quantity. How can the same thing be in two different categories?

This is the kind of problem that has kept scholars busy for centuries. Maybe Aristotle was confused. Maybe he changed his mind. Maybe “body” means different things in different contexts. Nobody really knows for sure.

And here’s another problem: some of Aristotle’s categories seem to be about relations between things rather than about things themselves. “Larger than” isn’t really a thing in the world—it’s a way that two things are related to each other. So is Aristotle really saying that relations are a fundamental kind of being? Or is he saying something else?

This gets complicated, but the upshot is this: Aristotle’s theory of categories is seen by many scholars as unfinished or even inconsistent. It’s more like a brilliant first attempt than a finished system. And that’s okay. Sometimes the most interesting ideas are the ones that don’t quite work.

What Does It All Add Up To?

The Categories is one of the most influential books in the history of philosophy, even though it’s very short and even though (or perhaps because) it raises more questions than it answers. It gave philosophers a framework for asking: what are the most basic kinds of things in the world? And how do we know?

Aristotle’s answers might not be the final word. But the questions he asked are still with us. Every time you think about whether something is “real” or “just a way of talking,” you’re doing a kind of category theory. Every time you wonder whether two things are the same kind of thing or different kinds, you’re doing category theory. It’s the kind of philosophy that’s so basic we often don’t even notice we’re doing it.

Key Terms

Term	What it does in this debate
Category	A fundamental type or kind that things can be sorted into
Primary substance	A particular thing (like Socrates or a specific horse) that isn’t a property of anything else
Secondary substance	A general kind (like “human” or “animal”) that particular things belong to
Said of	How a general category relates to the particular things that fall under it
Present in	How a property relates to the thing that has it
Accidental	Something that’s true of a thing but not part of its essential nature

Key People

Aristotle (384–322 BCE) — A Greek philosopher who studied under Plato, tutored Alexander the Great, and wrote about basically everything. He came up with the theory of categories and thought particular things were more real than abstract forms.
Plato (c. 428–348 BCE) — Aristotle’s teacher, who thought the most real things were abstract, perfect forms. Aristotle’s categories were partly a response to Plato.
Immanuel Kant (1724–1804) — A German philosopher who criticized Aristotle for not having a method for deriving the categories and then tried to do better. His own list of categories was different from Aristotle’s.
Thomas Aquinas (1225–1274) — A medieval philosopher and theologian who wrote detailed commentaries on Aristotle and tried to show that the categories could be systematically derived from basic principles.

Things to Think About

Do you think there are some kinds of things you can say about the world that don’t fit into any of Aristotle’s ten categories? If so, what would they be? If not, why not?
Imagine a language that has no word for “property” or “quality”—a language where you can’t say “the apple is red” but only “the apple reds” (as if redness were an action). Would speakers of that language have a different set of categories? Would they be missing something about reality?
Aristotle thought particular things (like a specific horse) were more real than general kinds (like “horse” as a species). Does that seem right to you? Or do you think the general kind is somehow more real or more important?
If you had to make your own list of the most basic kinds of things in the universe, what would it look like? Would it include things like “numbers”? “Possibilities”? “Feelings”?

Where This Shows Up

Science — When scientists argue about whether “species” are real categories in nature or just useful human labels, they’re arguing about categories.
Programming — Object-oriented programming uses “classes” and “instances” that work a lot like Aristotle’s secondary and primary substances. Programmers argue about how to design their category systems.
Everyday arguments — When you argue about whether something is “the same thing” or “a different kind of thing,” you’re doing category theory without knowing it.
Other philosophies — Many later philosophers (from Kant to contemporary metaphysicians) have made their own lists of categories, trying to improve on Aristotle’s or replace it entirely. The debate is still going.