The Most Famous Pair: What Are Things Really Made Of?

Here’s a strange thing about the world: you can keep dividing it, but you never get to the bottom.

You can cut a piece of wood in half, then cut one of those halves in half, and keep going. Eventually you’d get down to molecules, then atoms, then particles so small that nobody knows if you can split them further. But along the way, something weird happens. At some point, the wood stops being wood. You’ve changed what it is, not just how big it is.

This raises a question that medieval philosophers argued about for centuries: What are things actually made of, deep down? And not just physical things like wood and water, but everything—angels, souls, numbers, you. Is there some basic stuff that everything is built from? Or do different kinds of things have different kinds of building-blocks?

In the 1200s, a group of philosophers (mostly in Europe, mostly working at universities that were just being invented) got really into two ideas about this. They called them the binarium famosissimum—the “most famous pair.” They thought these two ideas belonged together, like peanut butter and jelly. But as we’ll see, it’s not entirely clear whether they really do fit together, or whether modern historians just imagined that they did.

The First Idea: Everything (Except God) Is Made of Matter and Form

The first idea is called universal hylomorphism (try saying that three times fast). That mouthful just means: everything that exists except God is a combination of matter and form.

What are matter and form? Imagine you’re making a sandcastle. The sand is the matter—it can become anything. The shape you give it—tower, wall, moat—is the form. Without sand, there’s no castle. Without a shape, it’s just a pile of sand. Everything physical seems to work this way. A statue is marble (matter) shaped like a person (form). Your body is cells and molecules (matter) arranged into you (form).

Now, universal hylomorphism says this isn’t just true for physical things. It’s true for everything that exists. Angels, souls, numbers, ideas—all of them are made of matter and form, just like sandcastles.

Wait—angels don’t have bodies. How can they have matter?

This is where it gets tricky. Universal hylomorphists said there are actually two kinds of matter. There’s the regular kind you can touch, which they called “corporeal matter.” And then there’s “spiritual matter”—a kind of stuff that isn’t physical but still plays the same role that matter plays in physical things. It provides something for form to work on.

Why would anyone believe this? Here’s the reasoning: Things that are “composite” (made of parts) don’t just happen. Something has to put them together. Everything that exists besides God was created by God. So everything besides God is composite—made of parts. And the most basic way to be composite is to have some indeterminate stuff (matter) that gets shaped by a determining principle (form). Therefore, everything besides God has matter and form.

Does that argument hold up? Philosophers still argue about it. But the key move is this: if you want to say that God is simple (not made of parts) and everything else is created (and therefore composite), then you need a way to explain how everything else is composite. Universal hylomorphism gives you that explanation.

The Second Idea: You’re Made of Layers, Like an Onion

The second idea is called plurality of forms. This one is about how many shapes a thing has inside it.

Everyone agreed that you can have many accidental forms—like the color of your hair, your mood, your weight. Those come and go without changing what you fundamentally are. But the question was: do you have more than one substantial form—more than one form that makes you what you essentially are?

The plurality-of-forms people said yes. They thought you’re built in layers, like an onion. At the very bottom is pure matter, kind of like a blank slate. Then you add a form that makes it a body (just a physical thing). On top of that, you add another form that makes it a living body. Then another form that makes it an animal. Then another form that makes it a human. Each layer limits and narrows down the previous one.

So when a human being dies and the soul leaves, what’s left? On this view, what’s left is still a body—not just a lump of matter. The “form of corporeity” (the form that made it a body in the first place) is still there. That’s why you can say “that’s Grandpa’s body” after he dies, rather than “that’s a pile of organic goo that used to be Grandpa.”

This mattered a lot to medieval Christians. They venerated the bodies of saints—people they believed were in heaven. If the body of a saint wasn’t really the saint’s body anymore after death, then venerating it would make no sense. The plurality-of-forms theory solved this neatly: the form of corporeity sticks around, so it really is the same body.

Do These Two Ideas Actually Go Together?

So here’s what’s strange. Modern historians often treat these two ideas as a natural pair—like they come as a package deal. They call them the “most famous pair” and treat them as the twin pillars of a whole school of thought.

But when you actually read the medieval philosophers, something interesting happens. Some of them held both ideas. Some held only one. Some rejected both. And nobody in the Middle Ages seems to have thought of them as a “pair” at all. The phrase binarium famosissimum shows up exactly once in surviving medieval texts, and it’s referring to something completely different (the division of substances into physical and non-physical).

So why do modern historians pair them up?

Here’s a possible answer. Suppose you think that language mirrors reality. When you say “The cat is black,” the word “cat” points to something in the world, and the word “black” points to some quality that thing has. Language breaks things down into subjects and predicates, and reality breaks down the same way.

Now think about describing that cat in more detail. You could say: “This is a body. This body is alive. This living thing senses things. This sensing thing is a cat. This cat is black.” Each step adds a new predicate—a new description. If language mirrors reality, then there must be a real thing in the cat for each of those descriptions. There must be a “body-form” that makes it a body, a “life-form” that makes it alive, an “animal-form” that makes it an animal, a “cat-form” that makes it a cat, and a “blackness-form” that makes it black—all stacked on top of each other.

That gives you a plurality of forms. And if you push this idea far enough, you get universal hylomorphism too, because even non-physical things can be described this way—they have a “what” (form) and a “that” (matter).

This is a neat picture. It’s simple. It explains a lot. But is it right?

The Other Side: Maybe Language Lies

The other camp said: hold on. Language doesn’t mirror reality that straightforwardly. When I say “This is a cat” and “This is a body,” I’m not identifying two different things inside the cat. I’m just describing the same thing at different levels of detail. The cat is a body—it’s not a body plus something else.

On this view, there’s just one substantial form for each thing. A cat has a single cat-form that makes it a cat. That form includes everything the cat is—being a body, being alive, being an animal, being a cat. You can’t peel these apart like layers of an onion. They’re all one thing.

Thomas Aquinas, a very famous philosopher from the 1200s, took this view. He said each substance has exactly one substantial form. When you die and your soul leaves, your body doesn’t keep its own separate form—it stops being a body in the proper sense and starts decaying. (This created problems for saint-veneration, which Aquinas tried to solve in other ways.)

Aquinas also rejected universal hylomorphism. He thought non-physical things like angels and souls aren’t made of matter and form at all. They’re made of something else: essence and existence (what they are, and the fact that they exist). That’s a different kind of composition, not matter-and-form.

Still an Open Question

So who was right? Nobody really knows. Philosophers still argue about whether things have “layers” of form or just one. They still argue about whether everything except God has to be composite, and what kind of composition that is.

The medieval debate was never fully resolved. Different philosophers gave different answers, and the arguments on both sides had real force. The “most famous pair” might not actually be a pair at all—it might be two separate questions that got tangled up by historians looking back.

But the core puzzle is still alive. When you look at anything—a cat, a person, a rock, an idea—what are you really looking at? Is it one simple thing, or is it layers of form stacked on top of each other, with matter at the bottom? And does the way we talk about things tell us what they really are, or is language just a crude map of a much stranger territory?

Appendices

Key Terms

Term	What it does in this debate
Hylomorphism	The view that physical things are made of matter (stuff) and form (shape/structure)
Universal hylomorphism	The more radical view that everything except God is made of matter and form, even non-physical things
Plurality of forms	The view that a single thing can have multiple “layer” forms stacked on top of each other (body-form, life-form, animal-form, etc.)
Substantial form	The form that makes something what it is at the most basic level (not just a temporary quality like color)
Form of corporeity	A form that makes something a body, distinct from any additional forms it might have
Spiritual matter	A hypothetical non-physical kind of “stuff” that could serve as matter for angels, souls, etc.
Composite	Made of parts; not simple

Key People

Solomon Ibn Gabirol (c. 1022–c. 1070) : A Spanish Jewish philosopher and poet whose book Fountain of Life became hugely influential in Christian Europe. He held both universal hylomorphism and plurality of forms, and many later thinkers followed him.
Thomas Aquinas (1225–1274) : A Dominican friar and philosopher who rejected both parts of the “most famous pair.” He argued that each substance has exactly one substantial form, and that non-physical things have a different kind of composition (essence and existence) rather than matter and form.
William of Ockham (c. 1287–1347) : A Franciscan philosopher who argued for plurality of forms partly because it made sense of why the body of a saint could still be venerated after death.

Things to Think About

Suppose you accept the “onion” view—that things have layers of form. Where does the layering stop? Do you keep adding forms all the way down? Could there be a form for “being made of atoms” underneath everything else?
When you describe something in different ways (“This is a body,” “This is an organism,” “This is a cat”), are you talking about different parts of the thing, or just the same thing from different angles? How could you tell the difference?
Is it possible that some things are not composite—that they’re truly simple, with no parts at all? What would something like that even be like?
Imagine a chair burns and turns into ashes. According to the “one substantial form” view, the chair-form is gone, and what’s left is just ashes. According to the “plurality of forms” view, the form of corporeity might still be there. Which view makes better sense of what happens when things change?

Where This Shows Up

Debates about identity : When someone gets a brain transplant or an artificial heart, are they still the same person? These debates about “what stays the same” echo the medieval arguments about forms and layers.
Biology and development : Scientists still argue about whether a developing embryo is “the same organism” at every stage, or whether it becomes a new kind of thing at different points. The medieval debate about forms of life is still running underneath.
Artificial intelligence : If a computer could think and feel, would it have a “mind-form” on top of its “computer-form”? Or would the computer-form itself have to change into something new? The medieval framework gives us a way to ask this question.
Everyday language : Every time you say “That’s not the same person anymore” about someone who’s changed drastically, you’re wading into the same philosophical puzzle about what makes something the thing it is.