How Do We Know What We Know? A Philosopher Who Imagined Learning from Scratch

A Statue That Learns to Think

Imagine a marble statue of a person—exactly like you in shape, but completely still and silent. It doesn’t move. It doesn’t feel anything. It has never smelled a rose, heard a bird, or felt the sun on its skin.

Now imagine that statue slowly coming to life. First, it gets just one sense: smell. All it can do is smell things. It can’t see, hear, touch, or taste. It can’t move at all.

What would that be like for the statue? What would it know?

This is the strange question that Étienne Bonnot de Condillac (say: “KON-dee-yak”) asked himself in 1754. Condillac was a French philosopher who wanted to understand how human beings come to know anything at all. He thought the answer was: everything we know comes from our senses. But he wanted to prove it—by imagining what it would be like to start from nothing.

The statue thought experiment was Condillac’s way of asking: if you gave someone senses one at a time, what could they learn? Could they build up everything we know—about space, about objects, about themselves, about other people—just from sensations?

What It’s Like to Only Smell

Here’s what Condillac thought would happen to the statue when it first smelled a rose.

The statue wouldn’t think: “I am a statue smelling a rose.” It wouldn’t think about itself at all, or about the rose as a separate thing. The statue would just be the smell of the rose. It would have no idea that it existed as a separate thing having an experience. It would be the experience.

If something else—say, a skunk—smelled different, the statue would “become” a different smell. But it wouldn’t know it was the same statue switching smells. Each smell would be its whole world.

If the statue smelled a rose and a skunk at the same time, the smells might blend together into one big smell. The statue wouldn’t pick them apart unless it had a reason to.

And here’s the key: the statue’s only guide would be pleasure and pain. Pleasant smells would make it want to keep smelling them. Unpleasant smells would make it want to escape. But since it couldn’t move, all it could do was try to remember a pleasant smell or imagine one when the current smell was bad.

What It’s Like to Have Two Senses

Now give the statue hearing, while it still has smell. This gets interesting.

If the statue hears a flute while smelling a rose, something different happens. A sound and a smell are so different that they don’t blend together the way two smells would. The statue would experience itself as both a smell and a sound at the same time. It would have what Condillac called a “double existence.”

But would it know it was one thing having two experiences? Not necessarily. It would just be two experiences at once.

Here’s a weird consequence: if a particular smell always came with a particular sound, the statue might not think of them as separate things at all. It might experience the smell as having that sound, and the sound as having that smell. They’d play the role of each other’s properties—like how you don’t think of a lemon’s yellowness and sourness as two separate things, but as parts of one thing.

This is actually Condillac’s theory of what we mean by “substance” or “thing.” When we call something a “thing,” we’re just saying that certain sensations tend to come together. There’s no mysterious hidden “stuff” underneath. A lemon is the yellow, sour, bumpy collection of sensations. There’s no ghostly lemon-essence behind them.

The Problem of Space

At this point, the statue still can’t move and has no sense of touch. Now give it sight.

When the statue first sees colors, something important happens. The colors appear outside of each other—one color here, another color over there. The statue would experience itself as “being” each color, and since the colors are in different places, it would experience itself as being outside of itself. As Condillac put it: “insofar as it is red, it experiences itself as being outside of itself insofar as it is green.”

But here’s the twist: would the statue notice that colors have shapes? Would it see that the red patch has edges and forms a circle?

Condillac said: probably not at first. The statue would need a reason to pay attention to the shapes. If it only cared about whether colors were pleasant or painful (red is nice, brown is boring), why would it bother to notice that the red patch is round? The shape is extra information the statue doesn’t need.

So the statue would have colorful, extended sensations—but it wouldn’t know they were shaped, wouldn’t see them as forming a continuous space, and wouldn’t have any real concept of space at all.

How Touch Teaches Us About the World

For Condillac, the sense of touch is what finally teaches us about space, about our own bodies, and about other objects.

Give the statue the ability to move its hands and feel things. Here’s what happens:

When the statue touches its own hand with its other hand, it feels two sensations of solidity at once—one in the touching hand, one in the touched hand. It experiences itself as being solid in two different places. When it moves its hand along its own arm, it feels a continuous series of solid sensations. If it does this repeatedly and gets the same sequence, it starts to understand that the arm is one continuous thing: its body.

When the statue touches something else—a table, say—it feels solidity without the answering sensation in the other hand. This absence teaches it that there is something else out there, separate from itself. The table isn’t it.

From there, the statue learns about shapes by moving its hands along objects. It learns about distance by moving toward things and feeling when they become touchable. Eventually, it learns to connect what it sees with what it feels. The colors it once just “was” become colors of objects. The smells and sounds it once just “was” become properties of things out there in space.

And here’s the amazing thing: once the statue reaches this point, it has built up almost everything we have. It now knows it has a body. It knows there are objects in space. It knows that smells, sounds, and colors belong to those objects. It has a sense of itself as a thing that continues through time. All of this came from just having senses and learning from experience.

Did Condillac Get It Right?

Philosophers have argued about Condillac’s thought experiment for 250 years. Here are some of the biggest problems:

The problem of memory. Condillac claimed that we get our sense of time—of past and present—from a kind of “echo” of sensation. When a smell lingers after the flower is gone, we experience the echo as a memory of the past. But critics say: why would an echo feel past rather than just fainter? How do we get the idea of “before” from sensation alone? Condillac never really explained this.

The problem of space. Condillac said colors are literally extended—they take up space in our experience. But he also said the mind is immaterial and unextended. How can an unextended mind have extended experiences? This is like saying a square peg fits perfectly into a round hole. A critic named René Réaumur accused Condillac of sneaking materialist assumptions (that the mind has spatial properties) into his supposedly spiritual philosophy.

The problem of the will. Condillac wanted to show that even our ability to choose and direct our attention comes from experience. But he never convincingly showed how. At some point, he seemed to just assume that we have free will as a basic feature of being human—which his theory was supposed to explain, not assume.

The problem of other minds. Condillac’s statue starts alone and builds up its knowledge from its own sensations. But how does it ever learn that other beings have minds like its own? How does it learn to communicate? This led Condillac into a whole separate theory about how language develops—which he thought was the key to higher thinking.

What About Animals?

Condillac’s theory had a strange consequence for animals. If all knowledge comes from sensation, and animals have sensations, why aren’t they as smart as us?

Condillac’s answer: animals have less developed senses of touch. Human hands, with their sensitive fingers, give us much richer information about the world than a dog’s paw or a bird’s claw. This difference in degree becomes a difference in kind.

Also, animals don’t develop language the way we do. Without language, Condillac thought, you can’t have proper memory, you can’t control your imagination, and you can’t do complex reasoning. Animals live “from moment to moment,” driven by habit and instinct, with no real sense of their own past.

But Condillac insisted this doesn’t mean animals are machines (as Descartes had claimed). They feel pleasure and pain. They learn. They have what he called “pre-linguistic reflection”—they can figure things out, just not as elaborately as we can.

What makes us truly different? According to Condillac, we can know God and moral laws. Because we can understand right and wrong, our souls are immortal—God will reward or punish us in an afterlife. Animals, lacking moral understanding, have nothing to be rewarded or punished for, so their souls (which Condillac thought were immaterial, like ours) simply cease to exist when they die.

Why This Still Matters

Condillac’s statue experiment is one of the most vivid thought experiments in philosophy. It asks us to imagine building a mind from scratch, piece by piece, and to ask: what’s essential? What do we really need to have a mind?

Modern scientists who study artificial intelligence and cognitive development ask versions of this same question. How much can a robot learn from its sensors alone, without any built-in knowledge? How does a baby, who starts with limited senses and no language, build up a picture of the world? These are Condillac’s questions, asked with modern tools.

His answer—that everything comes from sensation—is probably too simple. Most philosophers today think we need some built-in mental structures to make sense of our sensations. But Condillac showed how powerful learning from experience could be. And his central insight—that we often don’t notice what our senses are actually giving us until we have a reason to pay attention—remains a deep observation about how minds work.

Key Terms

Term	What it does in this debate
Sensation	The raw material of all knowledge, according to Condillac—what we get directly from our senses
Statue	Condillac’s imaginary being that starts with no knowledge and gains senses one at a time, to show how we learn from experience
Reminiscence	The experience of recognizing something you’ve sensed before—Condillac’s starting point for memory
Natural signs	Cries, gestures, and expressions we produce instinctively, without intending to communicate
Instituted signs	Signs we choose to use on purpose to stand for ideas—the beginning of language
Substance	The idea that things have an underlying “stuff” beneath their properties—Condillac thought this was just a word for a collection of sensations that reliably come together

Key People

Étienne Bonnot de Condillac (1714–1780) — French philosopher who spent his life trying to show that everything we know comes from our senses, using the famous “statue” thought experiment
John Locke (1632–1704) — English philosopher who argued that all knowledge comes from experience, but left room for the mind to combine and reflect on its ideas; Condillac pushed Locke’s ideas further
René Descartes (1596–1650) — French philosopher who thought animals were mindless machines; Condillac disagreed, arguing animals feel and learn
George Berkeley (1685–1753) — Irish philosopher who argued that physical objects don’t exist except as collections of sensations; Condillac’s theory sometimes seemed to lead to this conclusion, which he tried to avoid

Things to Think About

Condillac’s statue starts with one sense and gradually builds up knowledge. What if you had to design a robot that started knowing nothing—what would it most need to learn first? Would it need touch before sight, or the other way around?
When you have a strong smell or taste, do you “become” that experience, as Condillac’s statue does? Or are you always aware of yourself as a separate person having the experience? Which feels more accurate to your actual experience?
Condillac thought colors are literally extended in space—they take up room in your experience. Do you experience a patch of red as having size and location? Or do you experience it as a quality with no location, which you then judge to belong to a surface? Try to notice what actually happens when you look at something red.
If animals have sensations and learn from experience, why aren’t they as smart as humans? Condillac’s answer was partly about touch and partly about language. Does that seem right to you, or is there something else going on?

Where This Shows Up

Artificial intelligence and robotics — Engineers building robots that learn from sensors face Condillac’s question: how much knowledge must be built in, and how much can be learned from experience alone?
Child development — Psychologists who study how babies learn about objects, space, and other people are investigating the same process Condillac imagined, but with real experiments
Virtual reality — When you put on a VR headset and enter a simulated world, you’re experiencing sensations that your mind interprets as space and objects. Condillac’s ideas about how we learn to connect touch, sight, and sound are relevant to designing better VR
Debates about animal minds — The question of whether animals have consciousness, whether they can think, and whether they deserve moral consideration is still alive today—and Condillac’s arguments about animal souls and language are part of that history