Nagel’s Bat Argument

1. Introduction

Nagel’s bat argument is a thought experiment in the philosophy of mind that uses the case of bats to illuminate a tension between subjective experience and objective explanation. It is most widely known from Thomas Nagel’s 1974 article What Is It Like to Be a Bat?. The central idea is that there is something it is like to be a conscious organism, and that this subjective character of experience appears resistant to capture in the impersonal, third‑person terms favored by physical science.

The argument focuses on a specific contrast. On the one hand, there are objective physical facts about a creature’s brain, body, and behavior. On the other hand, there are phenomenal facts—what it is like for the creature itself. Nagel contends that even a complete catalogue of the former might leave us ignorant of the latter. This purported gap has become a focal point for debates over qualia, reductive physicalism, and the explanatory gap between mind and body.

Although the example centers on bats and their echolocation, commentators typically treat it as a general challenge: how, if at all, can a theory that aspires to objective, perspective‑independent description fully account for inherently perspective‑dependent phenomena like conscious experience? Different philosophical positions interpret the force of this challenge in divergent ways, ranging from arguments for non‑reductive physicalism or property dualism to attempts to reinterpret Nagel’s claims in purely epistemic or conceptual terms.

The bat argument is therefore frequently used as an entry point into wider issues about subjectivity and objectivity, the nature of consciousness, and the limits of scientific explanation.

2. Origin and Attribution

Nagel’s bat argument is generally traced to Thomas Nagel’s article:

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“Conscious experience is a widespread phenomenon… But it is not easy to say in general what provides its characteristic feature. … fundamentally 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.”

— Thomas Nagel, “What Is It Like to Be a Bat?” The Philosophical Review 83 (1974), p. 436

The paper was first published in 1974 in The Philosophical Review, one of the leading journals in analytic philosophy. It quickly became one of the most cited works in contemporary philosophy of mind and is now standardly anthologized.

2.1 Attribution and Naming

The thought experiment is variously referred to as:

• “Nagel’s bat argument”
• “What is it like to be a bat?” (after the article’s title)
• “The bat argument against physicalism”

These labels are used interchangeably in the literature. Some authors distinguish between Nagel’s broader argument about subjectivity and objectivity and the specific bat example as a vivid illustration within that argument.

2.2 Intellectual Lineage

Nagel’s reasoning draws on, and is often situated in relation to:

While these connections are often highlighted retrospectively, Nagel’s own work is usually credited with formulating, in a canonical analytic style, the challenge that “what it is like” for a subject resists straightforward physicalist reduction.

3. Historical Context

Nagel’s paper appeared in 1974, against a backdrop of dominant physicalist and functionalist approaches to the mind in analytic philosophy.

3.1 State of Philosophy of Mind in the 1960s–1970s

In this context, philosophers increasingly accepted that mental states are in some sense physical, yet were divided over how to account for conscious experience within a scientifically respectable framework.

3.2 Rise of Qualia and the Explanatory Gap

Nagel’s article contributed to the emergence of qualia as a central topic. Later authors, such as Joseph Levine (on the “explanatory gap”) and David Chalmers (on the “hard problem of consciousness”), often cited Nagel as an important precursor who had articulated, in a relatively concise way, the tension between a “view from nowhere” and first‑person phenomenology.

3.3 Relation to Broader Intellectual Currents

The 1970s also saw renewed interest in:

• Scientific realism and anti‑realism in philosophy of science, raising questions about the status of theoretical entities and explanatory completeness.
• Animal cognition and ethology, which were beginning to highlight complex behaviors in nonhuman animals.

Nagel’s use of a nonhuman animal as the central case intersected with these developments, inviting reflection on both the scope of human knowledge and the comparative study of minds. The bat argument thus entered debates not only about metaphysics of mind, but also about the epistemic limits of objective science in capturing conscious life.

4. The Argument Stated

Nagel’s bat argument can be stated in general terms without yet focusing on detailed logical reconstruction. It begins from the claim that conscious organisms have a subjective point of view: there is something it is like for them to be as they are. This fact, Nagel maintains, is not merely a matter of behavior or functional organization, but concerns the phenomenal character of their experiences.

He then contrasts two modes of understanding:

1. Objective understanding, characteristic of physical science, which aims to describe the world in perspective‑independent, third‑person terms.
2. Subjective understanding, which involves occupying or at least imaginatively approximating a point of view from the inside.

Nagel’s central contention is that even if we possessed a complete, idealized objective physical description of a creature, this description would still leave us without knowledge of what it is like to be that creature. The bat serves as a paradigmatic case because its central mode of perception—echolocation—differs radically from human perception, making imaginative projection especially difficult.

In very compressed form, the argument proceeds from:

• The existence of subjective facts about “what it is like” to undergo an experience.
• The apparent inaccessibility of these facts from the standpoint of purely objective, third‑person descriptions.
• The conclusion that standard reductive physicalism, which aspires to explain all facts in objective physical terms, faces a serious difficulty in accommodating consciousness.

Different commentators formalize and extend these steps in varying ways, but they typically agree that Nagel’s argument is meant to show that subjectivity poses a special challenge for reductionist theories of mind.

5. The Bat Thought Experiment

Nagel’s thought experiment invites readers to consider the case of a bat, chosen because bats are mammals (and thus plausibly conscious) yet possess a sensory apparatus—echolocation—that is sufficiently alien to human experience to strain our imaginative capacities.

5.1 Structure of the Scenario

Nagel asks us to perform a series of imaginative moves:

1. Acknowledge similarity and difference: Bats are sufficiently like us (being mammals) that it seems reasonable to assume they have experiences. Yet their way of perceiving the world is dominated by sonar rather than vision.
2. Attempt imaginative projection: We are asked to imagine “what it is like” for the bat, from the inside, to navigate and perceive via echolocation.
3. Recognize a limitation: Nagel argues that we quickly realize that we can only imagine what it would be like for us to behave and sense in bat‑like ways, perhaps by stretching and reshaping our own perceptual modalities, not what it is like for the bat with its own distinctive point of view.

5.2 Role of Echolocation

Bats emit high‑frequency sounds and interpret returning echoes to form a spatial representation of their environment. While humans can conceptually understand the physics and neurophysiology of this process, Nagel contends that such understanding does not yield the phenomenal texture of bat sonar experience. The felt character—how the environment “appears” in echolocation—is, on this view, inaccessible to us.

5.3 Philosophical Function of the Example

The bat case is used as an intuition pump to support several claims:

• There are facts about what it is like to be a bat.
• These facts are tied to the bat’s particular point of view.
• Full knowledge of the bat’s physical and functional organization does not automatically grant access to those facts.

The extremity of the sensory difference is meant to clarify a feature that, Nagel suggests, also applies to more familiar cases (such as other human minds): the subjective character of experience remains distinct from objective description, even when we have extensive scientific information.

6. Logical Structure and Premises

Commentators often reconstruct Nagel’s relatively informal discussion into an explicit argument. A common reconstruction emphasizes a sequence from the nature of experience to limits on reduction.

6.1 Core Premises

One standard formulation (closely aligned with the overview given earlier) is:

1. P1 – Subjective Character: Conscious experience has a subjective character; for any conscious organism, there is something it is like for that organism to be in its experiential states.
2. P2 – Perspective Dependence: This subjective character is essentially tied to a particular point of view (a first‑person perspective).
3. P3 – Objective Ideal: Physical science, as standardly conceived, aims at an objective, perspective‑independent description—a “view from nowhere.”
4. P4 – Epistemic Gap: Even complete objective physical knowledge about an organism (e.g., a bat) does not suffice to know what it is like to be that organism from its own point of view.
5. P5 – Explanatory Incompleteness: If complete physical description leaves out what it is like, then the subjective character of experience is not fully captured by that description.
6. P6 – Anti-Reductionist Step: If subjective character is not fully capturable in physical terms, then reductive physicalism about consciousness is incomplete or mistaken.
7. C – Conclusion: Therefore, reductionist physicalism faces a serious problem, and there is an explanatory gap between physical facts and facts about conscious experience.

6.2 Variations in Reconstruction

Different authors refine this structure in distinct ways:

Despite disagreements about how best to formalize the reasoning, most reconstructions preserve the central role of the bat example as evidence for an apparent disconnect between objective description and subjective experience.

7. Subjectivity, Objectivity, and Qualia

Nagel presents the bat case primarily to illuminate the relation between subjective experience and objective description. This has become central to discussions of qualia.

7.1 Subjective Character of Experience

Nagel characterizes a mental state’s subjectivity by asking whether there is something it is like for the organism to be in that state. This what‑it‑is‑like‑ness is:

• First‑personal: it is defined relative to a particular subject’s point of view.
• Non‑derivative: it is not simply a matter of how the subject behaves or what functional role the state plays.
• Seemingly incommunicable in full generality: descriptions can approximate but, Nagel argues, cannot fully convey the felt character to someone who lacks the relevant type of experience.

7.2 Objectivity and the “View from Nowhere”

Nagel contrasts this with an objective standpoint, which abstracts from any particular perspective:

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“The more objective we become, the less we can understand the subjective character of experience.”

— Paraphrasing Nagel’s general theme in What Is It Like to Be a Bat?

On Nagel’s picture, objectivity involves progressively stripping away idiosyncratic features of particular viewpoints to arrive at a perspective‑independent representation. Proponents of this way of thinking hold that this has been a mark of scientific progress. Nagel’s question is whether such progress can, even in principle, fully include the subjective character itself.

7.3 Qualia and Phenomenal Properties

Later philosophers often recast Nagel’s discussion in terms of qualia—the qualitative or phenomenal aspects of experience (e.g., the redness of red, the pain of pain). They interpret Nagel as arguing that:

• Qualia are essentially subjective, constitutively tied to points of view.
• Objective descriptions of physical states, even if true and complete, do not by themselves yield knowledge of these qualitative aspects.

Some theorists adopt this vocabulary explicitly to claim that qualia might be irreducible properties, while others use it more descriptively to mark the explanatory target that any theory of consciousness must address. In both cases, Nagel’s emphasis on the bat’s inaccessible subjective life is taken as a paradigmatic illustration of the tension between subjectivity, objectivity, and qualitative experience.

8. Implications for Physicalism and Reductionism

Nagel’s bat argument is widely interpreted as a challenge to reductive physicalism, though philosophers disagree about the strength and exact nature of that challenge.

8.1 Reductionist Physicalism Targeted

The primary target is a form of physicalism that holds:

• All facts, including mental facts, are in principle deducible from, or fully explainable in terms of, objective physical facts.
• A complete physical theory would suffice to capture all there is to know about the world, including consciousness.

Nagel’s reasoning, as usually read, suggests that even with complete physical information about bats (their neurophysiology, evolutionary history, functional organization), something remains left out: what it is like for them. If so, reductionist accounts are at best incomplete concerning consciousness.

8.2 Epistemic vs. Ontological Readings

Interpreters distinguish two broad implications:

Nagel himself tends to stress limits on current conceptual resources and the possibility of future concepts that might bridge the divide, which some read as suggesting an epistemic rather than straightforwardly ontological anti‑physicalist conclusion.

8.3 Broader Anti-Reductionist Motifs

Beyond physicalism narrowly construed, the argument has been used to question:

• Purely functionalist reductions that identify mental states solely with functional roles.
• Eliminativist views that deny the existence of phenomenal properties outright.
• Ambitious forms of naturalistic reduction that assume the methods successful in physics and biology will extend unmodified to consciousness.

Proponents of these implications claim that the bat argument underscores a distinctive feature of consciousness—its inherently perspectival nature—which complicates, or perhaps constrains, standard reductive strategies.

9. Key Variations and Related Arguments

Nagel’s bat argument has inspired modified versions and related thought experiments that aim to sharpen, extend, or reinterpret its core intuition about the difference between physical facts and phenomenal experience.

9.1 Variations on the Bat Scenario

Some philosophers develop alternative animal or alien cases to test the same structure:

• Alien or Martian minds: Building on Nagel, David Lewis’s “mad pain and Martian pain” case considers beings with radically different neural and functional organizations but similar or different experiences, probing how far physical or functional descriptions can go without capturing phenomenology.
• Inverted spectrum scenarios: Imagined cases where two people’s color experiences are systematically swapped (your “red” is my “green”) but behavior remains the same. These aim to generalize Nagel’s point about inaccessibility of others’ qualia, even in seemingly similar humans.

9.2 Related Anti-Physicalist Thought Experiments

Several well‑known arguments are often discussed alongside Nagel’s:

9.3 More Sympathetic Physicalist Reinterpretations

Some physicalists propose reinterpretations of the bat case:

• Phenomenal concepts strategy proponents use Nagel’s example to illustrate a gap in concepts (between phenomenal and physical ways of thinking), while maintaining that there is no underlying non‑physical property.
• Representationalist and information‑theoretic accounts sometimes claim that Nagel’s scenario highlights a need to refine our conception of objective description to include formally characterized perspectives, rather than demonstrating irreducible subjectivity.

Across these variations and related arguments, Nagel’s central theme—the apparent independence of “what it is like” from complete physical specification—serves as a reference point, either to be strengthened and generalized or to be explained away.

10. Standard Objections and Critiques

Philosophers have raised a variety of objections to Nagel’s bat argument. These critiques often focus on whether the argument justifies any strong metaphysical conclusion or even a robust explanatory gap.

10.1 Epistemic vs. Ontological Gap Objection

One influential line, associated with David Lewis, Daniel Dennett, and others, holds that Nagel’s argument at most reveals an epistemic gap: a limitation in what beings like us can know or imagine. According to this view:

• Our inability to know what it is like to be a bat does not show that phenomenal facts are non‑physical.
• It might simply reflect that we lack the relevant experiences or concepts to make the connection.

On this reading, Nagel confuses a limitation of perspective with a limitation of what physicalism can in principle explain.

10.2 Imagination and Conceivability Critiques

Critics also question Nagel’s reliance on imaginative failure:

• They argue that what we can or cannot imagine is a poor guide to the metaphysical structure of reality.
• Cognitive limitations, conceptual unfamiliarity, or psychological salience may all impede our imaginative capacities without implying anything about the reducibility of consciousness.

Dennett, for instance, contends that insisting on a special, ineffable “what it is like” risks reifying a confused or unexamined notion of qualia.

10.3 Objections to Nagel’s Conception of Objectivity

Another line of critique targets Nagel’s characterization of objective science as necessarily perspective‑less:

• Some philosophers suggest that science can, and increasingly does, incorporate indexical or perspectival information (e.g., self‑locating beliefs, observer‑relative facts).
• On this view, one can have an objective theory of subjective perspectives; Nagel is said to beg the question by defining objectivity in a way that excludes first‑person facts from the outset.

10.4 Phenomenal Concepts and Conceptual Dualism

Defenders of the phenomenal concepts strategy criticize any inference from Nagel’s premises to non‑physical properties. They claim that:

• The apparent gap between physical and phenomenal truths arises from the distinct conceptual roles of physical and phenomenal concepts.
• Once one recognizes this conceptual dualism, the argument no longer supports property dualism or anti‑physicalism.

Overall, critics tend to agree that Nagel has highlighted something important about our cognitive situation, but they dispute whether his reasoning justifies strong conclusions about the metaphysics of consciousness.

11. Responses and Proposed Resolutions

Philosophers sympathetic to Nagel’s core insight, as well as those seeking to reconcile it with physicalism, have offered a range of responses that attempt to “absorb” the bat argument without abandoning naturalistic commitments.

11.1 Non-Reductive Physicalism

Some theorists endorse non‑reductive physicalism, accepting that:

• Mental states are realized by physical states, but
• They cannot be reduced to, or fully explained in terms of, lower‑level physical descriptions.

On this view, Nagel is taken to show that reductionist versions of physicalism are inadequate, while leaving room for a layered ontology in which subjective facts supervene on, but are not reducible to, physical facts.

11.2 Property Dualism

Others interpret Nagel as supporting property dualism, the idea that:

• There is a single kind of substance (physical), but
• It instantiates both physical and irreducibly mental (phenomenal) properties.

Property dualists use the bat case, along with related arguments (e.g., Mary, zombies), to motivate the claim that phenomenal properties are distinct from physical or functional properties, even if closely correlated with them.

11.3 Phenomenal Concepts Strategy

Physicalists pursuing the phenomenal concepts strategy attempt to explain Nagel’s intuitions in purely conceptual terms:

• They propose that we possess special first‑person concepts for our experiences (phenomenal concepts).
• These are conceptually independent of physical concepts, which accounts for why knowing all the physical facts about bats does not automatically yield knowledge of what it is like for them.

On this approach, the bat argument reveals a conceptual gap rather than an ontological one.

11.4 Revisionary Accounts of Objectivity

Another response suggests that we should revise our understanding of objectivity rather than see it as excluding subjectivity:

• Objectivity might be redefined as the systematic integration of multiple perspectives, including first‑person perspectives, into a coherent framework.
• Under this broadened conception, an “objective science of subjectivity” becomes possible, potentially defusing Nagel’s subject–object dichotomy.

11.5 Mysterianism

Finally, mysterian responses (e.g., Colin McGinn) accept Nagel’s diagnosis as pointing to deep cognitive limits:

• Human minds may simply lack the right kind of concepts or cognitive architecture to bridge the gap between brain processes and conscious experience.
• Nagel’s bat argument is then taken as evidence that the mind–body problem might be unsolvable for creatures like us, even if it has a determinate (perhaps physical) solution in reality.

These responses provide different ways of accommodating the bat argument, distributing its force variously across metaphysics, epistemology, and theory of concepts.

12. Influence on Contemporary Philosophy of Mind

Nagel’s bat argument has become a central reference point in late 20th‑ and early 21st‑century philosophy of mind, shaping debates about consciousness, physicalism, and the nature of explanation.

12.1 Framing of the Consciousness Problem

The argument helped crystallize a standard way of posing the mind–body problem:

• As a challenge about subjective experience rather than merely about intentionality, rationality, or behavior.
• As a tension between first‑person phenomenology and third‑person science.

Subsequent discussions of the “hard problem of consciousness” and the “explanatory gap” typically cite Nagel’s paper as an early, influential formulation of this framing.

12.2 Impact on Key Concepts and Debates

Nagel’s work has contributed to:

12.3 Cross-Disciplinary Resonance

Beyond philosophy, the bat argument has influenced:

• Theoretical neuroscience and cognitive science, where it is often invoked to highlight the distinction between neural correlates of consciousness and subjective experience.
• Consciousness studies, including empirical research programs that explicitly aim to “bridge the gap” between third‑person data and first‑person reports.

In teaching and introductory texts, Nagel’s bat example is frequently used as the canonical thought experiment to introduce students and researchers to the puzzles of consciousness and the limits of scientific explanation, ensuring its continuing prominence in contemporary discourse.

13. Connections to Animal Minds and Ethics

While Nagel’s primary aim is theoretical, the bat argument has had notable implications for thinking about animal consciousness and related ethical concerns.

13.1 Comparative Consciousness

Nagel’s insistence that there is “something it is like” to be a bat implicitly supports the idea that many nonhuman animals have subjective experiences. This has influenced debates about:

• How far consciousness extends across species.
• The variety of experiential worlds, given different sensory and cognitive capacities.

Researchers in comparative psychology and cognitive ethology sometimes reference Nagel’s example to highlight both the plausibility of animal consciousness and the difficulty of understanding it from the human standpoint.

13.2 Epistemic Limits and Animal Experience

The bat argument emphasizes our epistemic limitations:

• Even with extensive behavioral and neuroscientific data, we may be unable to know in detail what it is like for nonhuman animals.
• This has led some philosophers to argue for epistemic humility in claims about the richness or paucity of animal minds.

At the same time, others suggest that Nagel’s focus on imaginative inaccessibility might risk underestimating animal consciousness if taken too literally, since it could encourage skepticism whenever experiences are hard to imagine.

13.3 Ethical Implications

The recognition that there is likely something it is like to be many animals has been used to support ethical positions:

Although Nagel himself does not develop a full ethical theory from the bat argument, his emphasis on the reality and opacity of nonhuman experiences has become part of the conceptual backdrop for contemporary discussions of animal minds and moral responsibility toward them.

14. Ongoing Debates and Open Questions

Nagel’s bat argument continues to generate active philosophical discussion, with several key points remaining contested.

14.1 Nature and Strength of the Anti-Physicalist Challenge

There is ongoing disagreement about:

• Whether the argument shows a temporary explanatory gap (likely to be closed by future science) or a permanent conceptual barrier.
• Whether it supports modest non‑reductive physicalism, robust property dualism, or merely reformist physicalism.

These disputes involve detailed questions about how to interpret Nagel’s claims about possibility, conceivability, and the nature of explanation.

14.2 Understanding “What It Is Like”

Philosophers continue to debate:

• How exactly to characterize what‑it‑is‑like‑ness: as a sui generis property, as a representational feature, as a structural or informational property, or as a feature of certain phenomenal concepts.
• Whether first‑person experience can be fully captured using structural, functional, or informational descriptions, or whether something remains inherently ineffable.

14.3 The Prospects for an Objective Theory of Subjectivity

Another open question concerns the possibility of a genuinely objective science of subjective experience:

• Some propose formal frameworks that integrate first‑person reports with third‑person data, arguing this responds to Nagel’s challenge.
• Others remain skeptical that any such framework could fully bridge the gap Nagel identifies, especially regarding what it is like for organisms radically unlike us.

14.4 Scope Across Species and Artificial Systems

The bat case also raises questions about:

• How to assess consciousness in animals evolutionarily distant from humans (e.g., cephalopods, insects).
• Whether Nagel’s reasoning extends to artificial systems such as advanced AI, and how one would determine whether there is “something it is like” to be such a system.

In all of these areas, Nagel’s argument functions less as a settled result and more as a conceptual touchstone, with philosophers using it as a point of departure for competing theories of consciousness, subjectivity, and explanation.

15. Legacy and Historical Significance

Over several decades, Nagel’s bat argument has acquired the status of a canonical thought experiment in the philosophy of mind, shaping how subsequent generations conceptualize the problems of consciousness.

15.1 Canonical Status

The paper What Is It Like to Be a Bat? is:

• One of the most widely cited articles in contemporary analytic philosophy.
• Routinely included in anthologies and syllabi on philosophy of mind, consciousness, and metaphysics.
• Often the first exposure many students have to the idea that there might be a principled gap between physical description and subjective experience.

This prominence has ensured that Nagel’s vocabulary—especially the phrase “what it is like”—has become standard in discussions of phenomenology.

15.2 Influence on Later Milestones

Nagel’s argument is frequently treated as a precursor to, and influence on, later landmark contributions:

Together, these developments have entrenched Nagel’s bat argument as part of a broader anti‑reductive tradition in the philosophy of mind.

15.3 Cross-Tradition and Interdisciplinary Resonance

Nagel’s focus on subjectivity has also been a point of contact between:

• Analytic philosophy and phenomenology, both concerned with first‑person experience but using different methods.
• Philosophy and empirical sciences of the mind, where the bat argument is invoked to articulate conceptual challenges for neuroscience and cognitive science.

15.4 Enduring Significance

Historically, the bat argument marks a shift from earlier behaviorist and purely functionalist emphases to a renewed centrality of phenomenal consciousness. Its enduring legacy lies less in a single definitive conclusion and more in reshaping the agenda: any comprehensive theory of mind is now generally expected to address, head‑on, the relationship between objective physical description and subjective experience that Nagel’s bats so memorably bring into focus.