What Is It Like to Be a Bat?

Back when I was in my early teens, before my friends and I discovered the far more interesting topic of girls, we would sit up late at night comparing ideas we’d read in science fiction books and ask ourselves philosophical questions. “How do I know that what I see as red,” we’d ask, “You don’t see as green? We can never know, because the color I see as red, you were taught to call ‘red’ too, even though it looks to you like what I call ‘green.’”

We would puzzle over that one, and a few years later, we expanded the question even wider. “How do you know that the colors I see are even in the same spectrum as those that you see? For all you know, I might be seeing colors that you can’t even conceive of, but if I could see through your eyes, your colors might be just as amazing to me.”

“Far out, man,” was the inevitable reply of the time, but the complete impossibility of ever really sharing another’s experience began to sink into, and inform, my adolescent mind. It made me feel lonely, too, for without supernatural powers of mind reading, no one would ever really know what it was like to be me. How can there ever really be true intimacy? “We live,” the Gang of Four would sing years later, “as we dream, alone.”

In 1974, Thomas Nagel, a philosopher at Princeton, published an essay called “What Is It Like to Be a Bat?” Imagine being a bat, Nagel suggested. There must be an experience of being a bat. But bats, Nagel wrote, are fundamentally different than us, in that they “perceive the external world primarily by sonar, or echolocation, detecting the reflections, from objects within range, of their own rapid, subtly modulated, high-frequency shrieks. Their brains are designed to correlate the outgoing impulses with the subsequent echoes, and the information thus acquired enables bats to make precise discriminations of distance, size, shape, motion, and texture comparable to those we make by vision. But bat sonar, though clearly a form of perception, is not similar in its operation to any sense that we possess, and there is no reason to suppose that it is subjectively like anything we can experience or imagine.”

This creates difficulties in imagining what it is like to be a bat. It doesn’t help to imagine that one has webbing on one's arms, which enables one to fly around at dusk and dawn catching insects in one's mouth; that one has very poor vision, and perceives the surrounding world by a system of reflected high-frequency sound signals; or that one spends the day hanging upside down by one's feet in an attic. “In so far as I can imagine this (which is not very far), it tells me only what it would be like for me to behave as a bat behaves. But that is not the question. I want to know what it is like for a bat to be a bat. Yet if I try to imagine this, I am restricted to the resources of my own mind, and those resources are inadequate to the task. I cannot perform it either by imagining additions to my present experience, or by imagining segments gradually subtracted from it, or by imagining some combination of additions, subtractions, and modifications.”

We may consider bat sonar to be a form of three-dimensional forward perception; we may believe that bats feel some versions of pain, fear, hunger, and lust, and that they have other, more familiar types of perception besides sonar. But we believe that these experiences also have a specific subjective character, which it is beyond our ability to conceive. And if there's conscious life elsewhere in the universe, it is likely that some of it will not be describable even in the most general experiential terms available to us. But even without the benefit of philosophical reflection, anyone who has spent time in an enclosed space with an excited bat knows what it is to encounter a fundamentally alien form of life.

Worse, the problem is not confined solely to bats or Martians, for it also exists between one person and another. For example, the subjective experience of a person deaf and blind from birth is not accessible to me, nor presumably is mine to him. In contemplating bats, Nagel notes, “we are in much the same position that intelligent bats or Martians would occupy if they tried to form a conception of what it was like to be us.

Although bats and Martians probably have experiences fully comparable in richness of detail to our own, the structure of our minds makes it impossible for us to understand. Even if someone were to develop concepts and theory that enabled us to think about those things, such an understanding would be permanently denied to us by the limits of our own nature.