What Is It Like to Be a Bat?

In a fifteen-page paper from 1974, Thomas Nagel quietly broke the most popular theory of the mind. The damage has not been repaired.

By the early 1970s, a confident orthodoxy had settled over the philosophy of mind. Consciousness, the orthodoxy said, was a physical process — a pattern of neurons firing — and one day neuroscience would describe it the way chemistry describes water. Mind would reduce to brain the way lightning reduced to electrostatic discharge. Just give us time.

Then Thomas Nagel published an essay with a strange title and a stranger argument. He didn't deny that minds are physical. He asked a question instead. And a generation of philosophers has been trying to answer it ever since.

The question

Nagel begins with what he calls a definition, though it is really a clue. An organism has conscious mental states, he says, if and only if there is something it is like to be that organism — something it is like for the organism. There is something it is like to taste coffee, to feel cold water on your hands, to see the colour red at sunset. There is, presumably, nothing it is like to be a stone.

This phrase — “what it is like” — sounds almost too modest to do real philosophical work. But Nagel is pointing at something every theory of mind has to account for: experience has a subjective side. It is always experience for someone, from a particular point of view. And it is precisely this side, he argues, that the reductive programme cannot reach.

Why a bat?

Nagel could have picked any animal. He picks a bat for a reason. Bats are mammals — close enough to us that almost no one doubts they have experiences. But the way they sense the world is profoundly alien. Most bats navigate by echolocation: they emit rapid high-frequency clicks and read the returning echoes to build a real-time three-dimensional picture of their surroundings.

We can describe this in physical detail. We know the frequencies, the timing, the auditory cortex involved. We can model the geometry the bat must be extracting. None of this, Nagel insists, tells us what it is like for the bat. Echolocation is not a form of any sense we have. It is not sight, even though it locates objects in space; it is not hearing, in the ordinary sense, even though its medium is sound. Imagining oneself with webbed wings, or hanging upside down, or eating insects, doesn't help: those are facts about being a human imagining a bat. The question was about being a bat.

And we cannot solve it by simply trying harder. The point is structural. Every act of imagining is performed from our point of view, with our sensory apparatus as raw material. To imagine the bat's experience would require already having it. The closest we can get from the outside is “something like sonar, but felt” — and the “felt” is precisely the part we don't know how to fill in.

The argument against reduction

The trouble is general. Reduction, in science, has always meant the same move: strip away the perspectives, find the structure underneath that everyone — human, Martian, instrument — would agree on. Heat became molecular motion; lightning became charge. The strategy works because the thing being reduced doesn't depend on a point of view. The molecules are the molecules whether anyone is looking or not.

Consciousness is the one phenomenon where this strategy collides with itself. The thing we are trying to explain is, by definition, tied to a point of view. To strip the point of view away is to strip away the very thing we wanted to explain. We end up with a thorough physical description and the original question untouched: but what is it like?

This is not a new mysticism. Nagel is not saying minds are made of soul-stuff, or that physics is wrong. He is making a much sharper point: our current concept of the physical was built precisely by ignoring the subjective. So of course it doesn't contain the subjective. Whether some future, broader concept of the physical could include it — that is exactly the question we don't yet know how to ask.

“Every subjective phenomenon is essentially connected with a single point of view, and it seems inevitable that an objective, physical theory will abandon that point of view.”

What the paper changed

Three things, mostly. First, it gave the field a vocabulary. Before Nagel, philosophers had circled around “qualia” and “raw feels” with embarrassment. After Nagel, “what it is like” became the standard handle for the subjective character of experience, and the test any theory of mind has to pass.

Second, it set up what David Chalmers, two decades later, would name the hard problem of consciousness: not how the brain processes information — that is hard but tractable — but why there is anything it is like to be a brain doing so. Chalmers' framing is more famous; Nagel's came first and is the parent of it.

Third, it changed what counts as a complete theory. A neuroscience that explained every input and output of a bat's brain, and yet left untouched the question of what the bat experiences, would not be wrong — it would be incomplete in a way we hadn't before known how to articulate. The bar got raised, and it stayed raised. Half a century on, no one has cleared it.

That is the quiet legacy of a fifteen-page paper. Not an answer. A question put so plainly that it cannot be unasked.