Nagel's "What Is It Like to Be a Bat?"

Thomas Nagel's 1974 paper "What Is It Like to Be a Bat?" (The Philosophical Review, vol. 83, no. 4) is among the most cited articles in twentieth-century philosophy of mind. Nagel deliberately chooses bats, rather than another person, as his test case for the limits of physicalist explanation, because bats perceive their environment chiefly through echolocation — emitting high-frequency sound pulses and interpreting the returning echoes to navigate and hunt in darkness — a sensory modality wholly unlike any human sense, yet one that clearly supports a rich, active, and evidently conscious mode of engagement with the world.