What Is It Like to Be a Bat?

In brief

Thomas Nagel (born 1937) published "What Is It Like to Be a Bat?" in The Philosophical Review in 1974. The essay does almost no biology. It uses the bat as a vivid case to make a general claim about the mind: an organism is conscious if and only if there is something it is like to be that organism, some way the world seems from its own point of view. A bat senses its surroundings by sending out high-frequency cries and reading the returning echoes. There is presumably something it is like to perceive the world that way. But that "something," Nagel argues, is tied to the bat's particular point of view, and we cannot reach it from ours. We can learn every physical fact about bat brains and sonar and still not know what it is like to be a bat. Nagel's conclusion is cautious but pointed: the subjective character of experience resists capture by the objective, third-person methods that physical science relies on. Consciousness is the part of nature that those methods seem built to miss.

The full treatment

The problem it answers

By the 1960s and 1970s, the dominant philosophies of mind were confidently physicalist. The identity theory held that mental states simply are brain states. Functionalism held that a mental state is defined by its causal role, what inputs trigger it and what outputs it produces, so that in principle it could be realized in any suitable system, brain or machine. Both views promised that mind would eventually dissolve into physics and computation, the way heat dissolved into molecular motion. Nagel did not deny that the mind is physical. He denied that we had any idea how the reduction was supposed to work. Every successful reduction in science, he noted, proceeds by moving away from the appearances toward an objective account: to explain heat we drop how warmth feels and describe kinetic energy instead. But with consciousness, the appearance, how it feels, is the very thing to be explained. A reduction that leaves out how experience feels has left out its subject. That is the tension the bat is designed to expose.

How the thought experiment works

Nagel chooses the bat deliberately. It is a mammal, so we grant it experience readily, yet its main sense is one we lack entirely. Bat sonar is not a modified version of any human sense; it is not like sight and not like hearing as we know it. So we cannot get at the bat's experience by analogy or extrapolation from our own. Nagel then blocks the obvious escape routes. Imagining that you have webbed arms, hang upside down, and eat insects only tells you what it would be like for you to behave as a bat behaves. It does not tell you what it is like for the bat. The point of view you want to occupy is the bat's, and the imaginative resources you bring are stubbornly human. The lesson generalizes. Facts about conscious experience are, in Nagel's phrase, connected to a single point of view, and an objective description is precisely one that abstracts away from any particular point of view. The two seem to pull in opposite directions.

The key distinction: objective and subjective

The heart of the essay is a contrast. Objective knowledge is knowledge available from many points of view, or from none: the mass of a bat, the frequency of its cries, the wiring of its cortex. Anyone suitably equipped can confirm these, human or Martian. Subjective facts are different. What it is like to hear an echo as a bat hears it is accessible only from the bat's own standpoint. Nagel's worry is that physical science advances by becoming ever more objective, stripping out the observer's perspective to reach a description that holds for everyone. That method is a triumph almost everywhere. But when the object of study is a point of view itself, the method removes the very feature it was supposed to explain. This is why Nagel says we do not even possess the concepts we would need to state how experience could be physical. He is not proving that it cannot be; he is insisting that the mind-body problem has been badly underestimated.

What Nagel is not claiming

Nagel is careful, and readers often overshoot him. He is not a dualist arguing for an immaterial soul. He accepts that mental events probably are physical events. He is not claiming bats are mysterious in some way other creatures are not; the argument runs equally for any conscious being, including your neighbor. And he is not saying consciousness is forever unknowable. His claim is narrower and stranger: our current concept of the physical, and the objective method that goes with it, gives us no grip on subjective character, and until we have some new conception that reconciles the two, physicalism is a promissory note we cannot yet cash.

Lineage

The essay stands in a long line of doubts about whether the mind fits into a mechanical world. Rene Descartes (1596 to 1650) split reality into extended matter and thinking substance precisely because thought seemed to resist description as mere mechanism, and Nagel inherits the puzzle while rejecting Descartes's two-substance solution. David Hume (1711 to 1776) noticed that when he looked inward he found only particular perceptions, never a self standing behind them, an early sign that the first-person view does not behave like an ordinary object of study. Ludwig Wittgenstein (1889 to 1951), in his remarks on private experience and his warning that "if a lion could speak, we could not understand him," pressed the thought that another creature's form of life can be closed to us. Nagel's own contribution was to sharpen the intuition into a precise objection to reductive physicalism and to give it an image that would not leave the reader's head. The essay directly seeded two of the most discussed arguments in later philosophy of mind: Frank Jackson's Mary's room (1982) and the framing David Chalmers made famous as the hard problem of consciousness (1995).

The strongest case for it

The argument's force is that it isolates something real and hard with a single clear example. Whatever your theory of mind, you have to say something about why there seems to be a felt quality to experience that a wiring diagram omits, and Nagel makes the omission vivid rather than abstract. The bat also neatly separates two questions that get run together: the easy questions of how the brain processes information, discriminates stimuli, and controls behavior, all of which yield to ordinary science, and the further question of why any of that processing is accompanied by inner experience at all. Nagel showed that answering the first set never automatically answers the second. And the essay is honest about its own limits. It does not overreach into proving dualism or declaring the problem insoluble; it claims only that we lack the concepts to close the gap, which is a claim critics have found remarkably difficult to dislodge in the decades since.

The strongest case against it

The reductionists have pushed back hard, and their replies are serious.

Daniel Dennett (1942 to 2024) argues that the whole appeal to an ineffable inner "what it is like" is a lingering illusion, not a datum that theory must respect. In Consciousness Explained (1991) and later work he treats the sense that there is a private residue left over after all the functional facts are in as itself a product of the brain's information processing, something to be explained away rather than honored. Grant Dennett this and Nagel's residue vanishes: there is nothing extra to capture.

Paul Churchland (born 1942) and Patricia Churchland (born 1943) reply that Nagel confuses a limit on our present imagination with a limit on reality. That we cannot now conceive how experience is physical is a fact about our concepts, they argue, and a maturing neuroscience may simply supply new ones, dissolving the mystery the way earlier science dissolved "vital force." An inability to imagine a reduction is not evidence that none exists.

A sharper technical objection targets the move from knowledge to metaphysics. Critics including David Lewis (1941 to 2001) and Laurence Nemirow argue that knowing what an experience is like is not knowing a special non-physical fact at all; it is acquiring an ability, a knack for imagining, recognizing, and remembering the experience. On this "ability hypothesis," you can possess every physical fact and still lack the know-how, with no gap in the facts themselves. If that is right, Nagel's intuition survives but his conclusion against physicalism does not follow.

Finally, some argue Nagel proves too little to matter. Even if there are perspectival facts we cannot access from outside, that may be an epistemic limitation on knowers, not a sign that consciousness escapes the physical order. The bat's experience could be wholly physical and still be knowable only from the bat's chair.

Where it stands now

More than fifty years on, the essay is among the most cited and most reprinted papers in the philosophy of mind, and its central phrase, "what it is like," has become the standard technical way to point at conscious experience. It did not settle the mind-body problem; it reopened it. The debate it helped launch now runs across philosophy, cognitive science, and neuroscience, from Chalmers's hard problem to the search for the neural correlates of consciousness to theories such as global workspace and integrated information. Committed physicalists still hold that the felt qualities will yield to the science, and they may be right. But almost no one now treats consciousness as an easy leftover to be mopped up once the functional story is told. Getting the field to feel the difficulty, and to feel it through a bat, is Nagel's lasting achievement.

Test yourself

Try, honestly, to imagine what it is like to perceive a dark room by echolocation, not to picture yourself flapping and squeaking, but to occupy the bat's sensory world from the inside. Notice how quickly the effort collapses back into human seeing and hearing dressed up as sonar. Now ask the real question: is that a limit on your imagination, which a cleverer brain or a future science might overcome, or a limit on what any objective, third-person description could ever contain? Where you land on that is where you land in the argument.