What Is It Like to Be a Bat?

"What Is It Like to Be a Bat?" is a paper by American philosopher Thomas Nagel, first published in The Philosophical Review in October 1974, and later in Nagel's Mortal Questions (1979). The paper presents several difficulties posed by consciousness, including the possible insolubility of the mind–body problem owing to "facts beyond the reach of human concepts", the limits of objectivity and reductionism, the "phenomenological features" of subjective experience, the limits of human imagination, and what it means to be a particular, conscious thing. Nagel famously asserts that "an organism has conscious mental states if and only if there is something that it is like to be that organism—something it is like for the organism." This assertion has achieved special status in consciousness studies as "the standard 'what it's like' locution." Daniel Dennett, while sharply disagreeing on some points, acknowledged Nagel's paper as "the most widely cited and influential thought experiment about consciousness." Nagel challenges the possibility of explaining "the most important and characteristic feature of conscious mental phenomena" by reductive materialism (the philosophical position that all statements about the mind and mental states can be translated, without any loss or change in meaning, into statements about the physical). For example, a reductive physicalist's solution to the mind–body problem holds that whatever "consciousness" is, it can be fully described via physical processes in the brain and body. Nagel begins by assuming that "conscious experience is a widespread phenomenon" present in many animals (particularly mammals), even though it is "difficult to say [...] what provides evidence of it." Thus, Nagel sees consciousness not as something exclusively human, but as something shared by many, if not all, organisms. Nagel must be speaking of something other than sensory perception, since objective facts and widespread evidence show that organisms with sensory organs have biological processes of sensory perception.