The opacity of experience

Nagel's mind-body problem and its ethical implications

Jan 29, 2026

The backyard stays dark for most of the day right now. For a moment, the sun peeks through the conifers and illuminates the frost like glitter on the pressure treated wood deck. I’m wrapped in my puffiest coat, scribbling thoughts into my notebook as if they’re the last ones I’ll have.

I’m sitting across a few small birds, the Pacific Wren, who remain in this place even in the dark winter months. They sing and dance together in the pockets of sun.

I think about what it would be like to be a Pacific Wren. To be a bird. I imagine the feeling of flight the way it feels to ski a steep mountain face. I imagine being able to sing in these high pitched tunes, and know exactly how to find warmth in the frosty morning sun. As a nature photographer, I’ve spent most of my life living for the moments and finding my own ways to tune into them.

I’m not the first person to daydream about what it’s like to fly, or to be someone or something else entirely.

Thomas Nagel famously contemplated this subject in his paper, What Is It Like To Be A Bat? Nagel draws attention to the mind-body problem by contemplating the difference between a human imagining the experience of a bat, and the actual conscious experience of being a bat. He challenges reductionist views that claim mental states can be fully explained by physical states (like how we reduce water to H2O or lightning to electricity).

For example, bats have a complicated echolocation system used to navigate the world. We can objectively describe what a bat does; we measure the frequencies it emits, track its flight patterns, map its neural activity, etc. But how can we begin to understand what echolocation feels like from the inside? What is the subjective character of navigating by sound?

This bears directly on the mind-body problem. For if the facts of experience - facts about what it is like for the experiencing organism - are accessible only from one point of view, then it is a mystery how the true character of experiences could be revealed in the physical operation of that organism.

Nagel then expands on the idea by comparing our understanding of bat echolocation to an alien’s understanding of lightning on earth:

A Martian scientist with no understanding of visual perception could understand the rainbow, or lightning, or clouds as physical phenomena, though he would never be able to understand the human concepts of rainbow, lightning, or cloud, or the place these things occupy in our phenomenal world.
…
Lightning has an objective character that is not exhausted by its visual appearance, and this can be investigated by a Martian without vision.

This illustrates that even complete physical knowledge of a bat, or lightning, or any physical property, doesn’t constitute knowledge of its subjective conscious experience.

If anyone is inclined to deny that we can believe in the existence of facts like this whose exact nature we cannot possibly conceive, he should reflect that in contemplating the bats 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.

The mind–body problem is uniquely hard because consciousness is essentially subjective, while physical theory is essentially objective, and right now we lack any conceptual bridge between these. The bat example dramatizes this gap and shows why familiar scientific reductions are inadequate in the case of the mind.

Why Nagel’s idea matters for thinking about experience

Consciousness, at this point, is the subjective experience of the conscious being. Nagel claims there is “something it is like” to watch a sunset, experience grief, or echolocate as a bat. Science seeks the objective physical states of the world independent of perception, but Nagel’s reflection forces us to ask new questions.

Can consciousness ever be reduced to a low-level physical description of elements? Since our conscious experience directly affects physical and mental health, how does this gap in our understanding between each other’s experiences affect how we produce medical treatments? What role does our conscious experience play in our perception of free will?

Reflection on what it is like to be a bat seems to lead us, therefore, to the conclusion that there are facts that do not consist in the truth of propositions expressible in a human language. We can be compelled to recognize the existence of such facts without being able to state or comprehend them.

The mind-body problem has long been contemplated by philosophers, with different schools of thought providing explanations like dualism, panpsychism (this one is super interesting), and physicalism, the latter of which we’ve looked at here in Nagel’s argument.

While Nagel’s paper is primarily about the limits of objective knowledge, I find it also carries an implicit ethical weight. If we cannot fully access the subjective experience of a bat (a creature we can study extensively), how much more limited is our access to the inner life of another human being? We share far more with other humans than with bats, yet each person’s conscious experience remains fundamentally private. Your pain, your joy, the particular quality of how the morning sun feels on your skin. These are facts I can never directly access, only infer and imagine.

This epistemic humility should shape how we approach each other. When we act as if we fully understand someone else’s experience, whether their suffering, their motivations, or their needs, we’re making the same mistake as imagining we know what it’s like to echolocate. The gap Nagel identifies isn’t just a philosophical puzzle, but a reminder that compassion requires acknowledging what we cannot know.

When I watch the Pacific Wren singing in the winter sun, I can’t help but project my own experience onto it. The warmth must feel good, the light must bring relief. I have no access, however, to what warmth or light or song actually mean to a wren. Recognizing this gap deepens my connection with these birds, with my surroundings, by replacing these thoughts with genuine wonder, present mindedness for my craft, and a greater respect for forms of experience I can never fully grasp.