The Heretic Who Thought the Mind Could Turn White

Here is a strange thing to try to think about: when you look at a white wall, or a red apple, or the blue sky, what actually happens inside your head? Most of us would say something like “my brain processes information about colors” and leave it at that. But in the 1330s, a Dominican friar named William Crathorn argued that this was not quite right. Actually, he said, when you look at a white wall, your mind literally becomes white. Not a metaphor. Not “your brain represents whiteness.” Your mind actually, physically, takes on the quality of whiteness.

This is, as you might guess, a very strange thing to claim. And it led Crathorn into some even stranger territory — about whether we can know anything at all, about what language is doing inside our heads, and about whether the world is actually made of tiny, indivisible particles. He was not trying to be weird for the sake of being weird. He was following an idea as far as it could go, and he ended up in places that made most of his fellow philosophers deeply uncomfortable.

The Problem of Getting the World into Your Head

Crathorn started with a problem that had bothered philosophers for centuries. When you see a tree, or remember a friend’s face, or think about the number seven, something is happening inside you. But what exactly? You are not literally holding a tree in your skull. You are not carrying your friend around inside your brain. Whatever is happening, it involves some kind of representation — something that stands for the thing out there.

Most philosophers before Crathorn had said that the mind uses something called a “species” (from a Latin word meaning “likeness” or “appearance”). Think of it like a stamp pressing an image into wax. The wax does not become the stamp — it just takes on its shape. Similarly, your mind receives a likeness of the tree without becoming a tree. The likeness is a kind of ghostly copy, less real than the original thing.

Crathorn thought this was a cheat. If the likeness is real enough to carry information about the tree, he argued, it must be real in the same way the tree is real. A copy of whiteness is still whiteness. So when you perceive a white wall, the thing inside your head must actually be white. Not pretending to be white. Not representing white. White.

This gets even stranger when you think about it. What happens if you think about a rock? According to Crathorn, the species of a rock would have to be a rock — which would mean your mind would turn into a rock. He found this ridiculous. So he decided that the human mind cannot think about substances (things like rocks, trees, people) directly at all. We can only think about their qualities — their colors, textures, temperatures, sounds. When we think we are thinking about a rock, we are really only thinking about a collection of qualities that we have learned to call “rock.”

The Brain as a Processing Machine

Now, this part gets a bit technical, but the payoff is worth it. Crathorn believed that all this species-stuff happened in specific parts of the brain. He used the medieval map of the brain, which divided it into three chambers connected by nerves. The first chamber handled sensation and imagination — what you directly perceive. The second handled reasoning and putting ideas together. The third handled memory.

This might not sound revolutionary to us — we know the brain has different regions for different jobs. But for Crathorn, the point was that all these functions were physical. Sensation, imagination, memory, and thinking were not different kinds of mental events. They were just species moving through different parts of the brain. There was no ghostly “mind stuff” separate from the physical brain. Your thoughts were physical things, located in physical space.

The Problem of Being Sure about Anything

Here is where things get really uncomfortable. If what you directly perceive is always a species inside your own head — something that is literally a quality of your own brain — how can you ever be sure that the outside world is anything like what you perceive? The white in your brain might match the white of the wall. Or it might not. You have no way to check, because you can never get outside your own head to compare.

This is a major skeptical problem. Crathorn saw it clearly. He said that by natural means — just using your senses and your reasoning — you cannot be absolutely certain that the external world exists the way you think it does. The best you can do is be certain that the qualities inside your head exist. But whether they correspond to anything outside? That is not something your senses can guarantee.

Crathorn’s solution was to appeal to God. He argued that it is built into the nature of things — known by itself, without proof — that God would not create a world where your perceptions systematically lie to you. If God let you be permanently deceived about the external world, that would make God a trickster. And that, Crathorn thought, would contradict what God is.

But even he seemed unsure about this. So he went back to an older argument, from Augustine. You can at least be certain that you exist, because if you are doubting whether you exist, there must be something doing the doubting. “I doubt, therefore I am” was a small island of certainty in a sea of uncertainty. Several hundred years later, René Descartes would use almost the same argument.

Language: The Strange Idea That You Think in English

Crathorn did not stop with perception. He also had a radical theory about language.

Most medieval philosophers thought that underneath all the different human languages — Latin, English, French, Arabic — there was a universal “mental language” that everyone shared. This mental language was made of concepts that you acquire naturally as you encounter the world. When you see a dog, your mind naturally forms the concept DOG. This concept is the same for everyone, regardless of what spoken word you use for it.

Crathorn could not accept this. Remember: for him, the only things in your mind are qualities — physical species of color, texture, sound, and so on. You can have a natural likeness of a dog’s brown fur or its bark. But what about the word “dog” itself? Or words like “all,” “but,” “if”? These have no color, no texture, no sound of their own. They are purely conventional — agreed upon by communities of speakers.

So Crathorn argued that mental language is not natural and universal. It is just as conventional as spoken language. When you learn to speak English, you internalize English. Your thoughts become structured by the patterns and vocabulary of English. If you had learned Chinese, your thoughts would be structured differently. There is no universal language of thought underneath it all.

This was a hugely controversial position. Almost no other philosopher of his time agreed. But it makes a certain kind of sense given his other views. If thoughts are just physical qualities in the brain, and those qualities come from your senses, then abstract words like “justice” or “if” cannot have natural mental images. They have to be learned from other speakers.

Blowing Up the Categories

Now, Crathorn went after something even bigger. For more than a thousand years, most philosophers had accepted Aristotle’s list of ten categories — ten basic kinds of things that exist. Substances (like a person or a tree). Qualities (like red or hot). Quantities (like three meters). Relations (like “larger than”). And so on.

William of Ockham, a slightly older philosopher Crathorn was always arguing with, had reduced the ten to two: substance and quality. Everything else, Ockham said, was just a way of talking about substances and qualities.

Crathorn went further. He argued that the whole system was wrong. The distinction between substance and quality, he claimed, does not really hold up. Consider: when you heat a piece of wood, the wood itself gets hot. But so do all the qualities of the wood — its color, its texture, its smell. They all change from one state to their opposite. So the thing that makes substance different from quality — the ability to take on opposite qualities — does not actually distinguish them.

Crathorn’s conclusion was that the same thing could be called a substance, a quality, a quantity, or a relation depending on how you look at it. The categories were not real divisions of the world. They were just ways of talking. Philosophical conventions, not truths about reality.

Atoms and the Strange Physics of One Speed

The last piece of Crathorn’s system is his atomism. He believed that everything is made of tiny, indivisible particles. These were not mathematical points — zero-dimensional dots. They were real physical chunks with size and shape. There were atoms of gold, atoms of lead, atoms of different kinds of stuff.

This led to a problem that had bothered atomists since ancient Greece. If atoms are indivisible — with no parts — how do they touch each other? If two atoms are in contact, they should occupy the same place. But two things cannot occupy the same place at the same time.

Crathorn’s answer was clever. Atoms occupy places that are themselves atomic — tiny indivisible units of space. Two atoms can be in contact by occupying adjacent atomic places. They do not overlap; they just sit next to each other. This kept the idea of indivisible particles working without running into logical contradictions.

But the really wild implication was about motion. Crathorn argued that if an atom moves continuously — without stopping — it can only move at one speed. The fastest possible speed. Think about it: if time is also made of atoms (tiny indivisible units of time), then in one unit of time, an atom can move from one atomic place to the next. That is the maximum speed. Any slower motion must involve pauses — the atom moves, stops for a bit, then moves again. What we experience as different speeds is actually a matter of how many pauses there are between movements.

This is not how physics works in our world. But it is a remarkably consistent attempt to work out what the world would have to be like if atoms and time were both made of tiny indivisible units.

Why This Matters

You have probably never heard of William Crathorn. He was not famous in his own time, and he is barely remembered now. Most histories of medieval philosophy skip over him entirely. But he represents something important: the willingness to follow an idea wherever it leads, even into territory that seems absurd.

Crathorn started with the simple observation that what is in your mind must be real. He ended up with a world where minds literally turn white when they see white, where you can never be fully sure the outside world exists, where you think in the language you were taught, and where everything is made of atoms that can only move at one speed.

Not all of these ideas were right. Some of them are clearly wrong. But Crathorn was not trying to be right. He was trying to see what a consistent picture of the world would look like if you took certain starting points seriously. That is a deeply philosophical thing to do. And it means that even a forgotten friar from the 1330s can still make you stop and wonder: what really happens inside your head when you see something white?

Key Terms

Term	What it does in this debate
Species	The mental likeness or representation of an external thing; for Crathorn, it is physically real, not a ghostly copy
Quality	A property like color, texture, or temperature; Crathorn thought we can only directly perceive qualities, not substances
Substance	A thing that exists on its own, like a rock or a tree; Crathorn thought we could never be sure substances exist
Mental language	The language your thoughts are “written in”; Crathorn thought it was conventional, not natural and universal
Atom	A tiny, indivisible particle of matter; Crathorn believed everything was made of them
Skepticism	The view that we cannot be certain about some things; Crathorn was a skeptic about the external world

Key People

William Crathorn (c. 1300–1360s): A Dominican friar who lectured at Oxford in the 1330s and developed some of the most radical philosophical ideas of his time, including the claim that the mind becomes physically white when perceiving white.
William of Ockham (c. 1287–1347): A Franciscan philosopher famous for “Ockham’s Razor” (the principle that simpler explanations are better); Crathorn constantly argued against him, even though they shared some starting points.
Augustine (354–430): An early Christian philosopher who argued that you can be certain of your own existence because doubting proves there is something there to doubt; Crathorn used this argument against skepticism.

Things to Think About

If Crathorn is right that what is in your mind is physically real, what would happen if you try to think about something impossible — like a square circle? Would your brain actually contain a square and a circle at the same time? What would that even mean?
Crathorn said you cannot be certain the external world exists. But most of us go through life assuming it does. Is that a mistake? Or is it okay to act as if things are real even if you cannot prove it?
If thoughts are just physical qualities in the brain, and if mental language is learned from your community, does that mean people who speak different languages actually think differently? Could there be thoughts you cannot think because your language does not have the words for them?
Crathorn’s atomism said everything moves at one speed, with pauses making things seem slower. Can you think of any way to test this? What would have to be true about time and space for this to work?

Where This Shows Up

The idea that you can never be sure the outside world is real appears in movies like The Matrix and in some versions of virtual reality. If you cannot tell the difference between the real world and a perfect simulation, does it matter?
The idea that language shapes thought is a live debate in linguistics and psychology today. Do people who speak different languages see the world differently?
Modern neuroscience confirms that different parts of the brain handle different jobs, just as Crathorn’s three-chamber model suggested. Though obviously we know a lot more now about which parts do what.
Atomism turned out to be basically right — matter is made of tiny particles — but Crathorn’s specific version (everything moves at one speed with pauses) was wrong. Modern physics has a much stranger story about what happens at the smallest scales.