Why science can't tell us what it's like to be a bat
A neuroscientist could map every single neuron and sonic echo in a bat's brain, yet still not understand what it actually feels like to navigate using sonar. Philosopher Thomas Nagel argued that subjective experience has a unique, first-person perspective that objective physical descriptions can never fully capture. Even if we knew everything about bat biology, we would still only imagine being a human behaving like a bat.
The Question at the Heart of Consciousness
In 1974, American philosopher Thomas Nagel published an essay titled "What Is It Like to Be a Bat?" in the academic journal The Philosophical Review. The paper addressed one of the most persistent puzzles in philosophy and science: the mind-body problem. At the time, materialist theories of mind were gaining widespread popularity. Many philosophers and scientists believed that conscious mental states could eventually be fully explained by physical processes in the brain, much like chemical reactions explain digestion or molecular motion explains heat.
Nagel challenged this growing consensus by offering a precise definition of conscious experience. He argued that an organism possesses 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 itself. Whether an organism feels pain, perceives light, or senses danger, these events are accompanied by an inner, felt quality. This subjective character of experience means that consciousness cannot be treated merely as a mechanical input-output system, because it possesses an inherently first-person reality.
Why the Bat Serves as the Perfect Example
To illustrate the divide between physical description and subjective experience, Nagel deliberately chose an animal that is biologically close to humans yet sensorially alien. Bats are mammals, sharing much of our basic physiology, evolutionary history, and neural architecture. Because of this common mammalian heritage, it is reasonable to assume that bats are conscious creatures with their own subjective experiences, rather than mindless biological automatons.
At the same time, microbats perceive the external world primarily through echolocation, emitting high-frequency auditory pulses and detecting the returning reflections to navigate and hunt in total darkness. While humans possess senses of sight, hearing, touch, taste, and smell, human sensory organs provide no direct equivalent to navigating via reflected sound waves. Echolocation is not simply a variation of human hearing; for a bat, it functions as a primary mode of three-dimensional spatial perception, creating a perceptual world fundamentally unlike our own.
The Failure of Human Imagination
A common response to Nagel's thought experiment is to attempt to imagine what flying through the dark and catching insects using sonar feels like. One might picture hanging upside down by one's feet in an attic, navigating by hearing clicks, or having webbing stretched between extended fingers. However, Nagel pointed out that this exercise misses the central point. When a person performs this imaginative leap, they are merely imagining what it would be like for a human being to behave like a bat.
Our imagination is strictly limited by the resources of our own sensory and conceptual hardware. A human mind can only extrapolate from existing human experiences—such as closing one's eyes and listening to echoes in a hallway. A bat's brain, nervous system, and sensory apparatus, by contrast, have developed over millions of years to process sonar information directly. Knowing what it is like for a bat to be a bat requires experiencing the world through a bat's unique point of view, which remains fundamentally closed to human subjectivity.
The Limits of Scientific Objectivity
The central conflict in Nagel's argument lies between the nature of scientific progress and the nature of consciousness. Traditional scientific reduction works by moving away from subjective appearances toward an objective, observer-independent description of reality. To understand lightning, science moves away from the human visual impression of a bright flash and describes electrical discharge. To understand heat, physics abandons the subjective feeling of warmth and describes the average kinetic energy of molecules.
This standard reductive method breaks down when applied to conscious experience itself. Subjective experience is tied by its very definition to a specific, first-person point of view. When scientists attempt to describe consciousness purely in third-person, physical terms—such as patterns of neurochemical firing across a cortex—they strip away the specific point of view that constitutes the phenomenon. In doing so, they leave behind the subjective character they set out to explain in the first place.
Understanding the Explanatory Gap
Nagel did not claim that physicalism is necessarily false, nor did he argue that the mind must be made of a non-physical substance like a soul. Instead, he argued that physicalism is an assertion we currently have no conceptual framework to comprehend. We do not yet understand how a physical brain state and a subjective conscious experience could be the exact same thing.
To demonstrate this, Nagel used the analogy of telling someone before the advent of modern chemistry that matter and energy are equivalent, or that sound is a wave in the air. Without the necessary theoretical background, such claims seem unintelligible. Similarly, simply declaring that mental states are brain states does not bridge the conceptual divide between objective neurobiology and the felt, first-person reality of living creatures.
Criticisms and Continuing Influence
Nagel's paper sparked decades of intense philosophical debate and helped define contemporary philosophy of mind. Critics of Nagel, including philosopher Daniel Dennett, argued that Nagel overstated the irreducibility of subjective experience. Dennett and other functionalist thinkers contended that third-person scientific investigation can eventually account for consciousness, arguing that what we call subjective qualia are functionally explainable through cognitive mechanisms and behavioral capacities.
Despite such critiques, Nagel's core argument established a vital distinction in the study of the mind, directly paving the way for later formulations like the hard problem of consciousness. It demonstrated that even if a future neuroscientist could measure every electrical impulse, acoustic frequency, and synaptic connection in an animal's nervous system, an objective map of physical facts remains fundamentally distinct from the internal experience of the creature living through them.
Key takeaways
•Consciousness requires a subjective point of view: an organism is conscious only if there is something it is like to be that organism.
•Objective science progresses by eliminating observer-dependent viewpoints, but this method fails for consciousness because the subjective perspective is the essential phenomenon under study.
•Imagining animal life through human sensory categories only reveals what it would feel like for a human to act like an animal, not what the animal experiences from its own perspective.
•Thomas Nagel did not claim physicalism is impossible, but rather that we currently lack the conceptual tools to understand how physical brain states produce subjective experience.