The essay begins by changing the scale of the mind-body problem. For Thomas Nagel, consciousness is not a local difficulty that neuroscience can isolate within the relation between brain, behavior, and experience. If physical organisms genuinely possess subjective points of view, think in response to reasons, and recognize values, then the cosmic history that produced those organisms must make the emergence of all these properties intelligible. Nagel’s target is therefore not the ordinary practice of physics, chemistry, or biology. It is a general worldview extrapolated from their successes, according to which everything that exists could in principle be explained through the elements and laws of physics and their neo-Darwinian extension into the living world.

This materialist ambition partly derives from the method that made modern science possible. Galileo and Descartes separated a quantifiable external reality, defined by spatiotemporal properties, from subjective appearances such as color, sound, and smell. That disciplined exclusion of mind enabled immense progress. Yet it incurs a conceptual debt once science tries to place conscious subjects back inside the physical reality from which they were abstracted. Molecular biology describes the composition and operation of organisms, while evolutionary theory explains their transformation through heritable variation and natural selection. It does not follow, Nagel argues, that lived experience, rational thought, or value can be reduced to this physical history.

Alongside this philosophical argument, Nagel expresses skepticism, explicitly identified as the judgment of a widely read layman, about the origin of life and the supply of viable variation required by evolution. Natural selection can operate only after reproducing organisms and selectable mutations are available. It therefore cannot by itself explain the first appearance of life or the production of all the possibilities on which selection acts. Nagel does not claim to possess a competing biological demonstration. He argues that the passage from lifeless matter to the genetic code and then to conscious organisms should not be declared adequately explained as a matter of principle. His doubt does not arise from religious faith, and he rejects intervention by a designer as an explanatory endpoint.

The positive starting point is a demand for intelligibility. Science assumes that the world has an order inquiry can uncover, and Nagel resists treating this intelligibility as merely a brute fact. An adequate conception should explain both nature and the existence within nature of beings capable of understanding it. Materialism risks dissolving mind into an impoverished vocabulary, dualism places two orders side by side without unifying them, and theism explains nature through an external intention whose operation remains obscure. Even a pluralism that abandons any common view leaves unanswered how its different perspectives belong to one reality. Nagel therefore seeks, without claiming to possess, an expanded naturalism in which mind is a fundamental aspect of the world.

Consciousness provides the first decisive test. Behaviorism tried to analyze mental states through behavior, observable dispositions, or the conditions under which mental descriptions are warranted. It left out the experienced inner state itself. Psychophysical identity theory then proposed that a pain or sensation is identical with a brain event, as water is identical with H2O. For Nagel, however, the analogy fails. Molecular properties explain the properties of water, whereas a physiological description, however complete, does not appear sufficient to explain why a process has a felt quality. Functional and causal analyses may tell us what a mental state does, but not why there is something it is like to be in that state.

This irreducibility transforms the evolutionary question as well. A history of organisms that explained only their physical adaptations and behavior would not explain their appearance as subjects. To say that consciousness accompanies certain structures as a side effect would record a correlation, not show why conscious beings were likely to arise. Nagel distinguishes here between identifying a cause and explaining an event under a particular description. The physical mechanisms of a calculator can produce the shape “8,” but explaining why it gives the correct answer requires reference to its algorithm and, for this artificial object, its design. Likewise, biological history must make intelligible the appearance of consciousness as consciousness, though without appealing to a designer.

Nagel organizes the possible solutions around two questions. A constitutive account asks how a physical system can also be mental. An emergent theory would introduce psychophysical principles linking consciousness to complex biological organization. A reductive but nonmaterialist theory would attribute to elementary constituents a nature richer than physics describes. Because organisms consist of the same matter as everything else, this neutral monism becomes universal and, in its most schematic form, approaches panpsychism. A historical account then asks how conscious systems arose. It may appeal to efficient causation, a natural teleological tendency, or intentional intervention. Combining the two constitutive options with the three historical options yields six abstract possibilities.

None of these possibilities is offered as a finished theory. Systematic emergence preserves a break between physical elements and a conscious whole that may still look magical. Monism promises greater unity, but does not specify protomental properties or show how they compose a single subject. Above all, it does not explain why those constituents should form life within the available time. Natural teleology would instead add laws of development or self-organization that increase the probability of certain paths toward complexity, life, and mind. Such laws would have to be universal and active at more elementary levels, not retrospective descriptions of the one terrestrial history we know. This Aristotelian hypothesis without intention remains uncertain, but Nagel sees no justification for ruling it out in advance.

Cognition introduces a difficulty distinct from subjectivity. Human beings do not merely perceive and desire. They distinguish appearance from reality, formulate laws, recognize contradictions, and subject their impulses to reasons. Language, collective justification, and criticism extend this capacity. An evolutionary history might explain why certain cognitive dispositions favored survival and then imagine their cultural extension into science. It cannot, however, establish the authority of reason without already presupposing that authority. Judging an evolutionary explanation probable requires logic, evidence, and rational assessment. Any attempt to validate those norms by tracing their origin is therefore circular.

Nagel’s example contrasts perception with inference. Seeing a tree depends on a causal chain connecting the object, reflected light, and a visual system shaped by evolution. Recognizing that contradictory beliefs cannot all be true seems instead to respond directly to a logical necessity. If someone believes he is driving south while the sun rises on his right, his background knowledge and the detected inconsistency give him a reason to revise that belief. Reducing this revision to an adaptive aversion to contradictions would miss what justifies the conclusion. Reason is fallible in its complex uses, but any correction must ultimately appeal to better reasoning. Its natural history must therefore explain a capacity whose authority claims to exceed its local usefulness.

The same conflict returns in practical thought. On a subjectivist account, evaluative truths ultimately depend on our motivations, sentiments, or reflective dispositions such as impartial self-interest and benevolence. Nagel’s realism reverses the order of explanation: our responses attempt to track reasons that can vindicate or condemn them. If failing to brake will cause a dog to be run over, that fact counts against inaction. The principle that avoiding grievous harm to a sentient creature provides a reason is not made true by some further preference. Realism thus does not add a mysterious moral substance to the universe. It treats some normative truths as basic, while conceding that its credibility depends on the results and corrections achieved through moral reflection.

The Darwinian objection, developed through Sharon Street’s argument, is especially powerful. Selection can explain aversion, care for offspring, cooperation, and other dispositions through their contribution to reproductive fitness, whether the resulting judgments are objectively true or systematically false. Consistently deceptive physical perception would harm survival, but evolution need not presuppose that pain is really bad in order to favor its avoidance. Nagel accepts the force of this dilemma but refuses to abandon realism. Pleasure and pain are, on his account, both biologically adaptive motivations and experiences that are genuinely good or bad. Value then extends pluralistically to the goods proper to diverse forms of life and to the reasons rational subjects can recognize. If this interpretation is correct, the history of life must explain not only adaptation, but the entrance of value into the world.

Teleology becomes the candidate that connects the three inquiries. If life makes consciousness, knowledge, and value possible, its appearance may depend on a natural predisposition to form organizations capable of those developments. Certain future states would receive a higher probability not merely because of their immediate properties, but because they are stages on paths toward more complex systems. In the domain of value, the boldest formulation is that life is not merely followed by value. Life arises in part because it is a condition for value to be realized and recognized. This orientation would be no agent’s decision. It would belong to the historical laws of nature itself.

This hypothesis does not eliminate natural selection. Nagel preserves its major role in determining the particular forms organisms take within changing environments. His proposed revision concerns the source of the biological possibilities offered to selection and the general probability of life, consciousness, and reason. It therefore differs from pure chance, physical laws wholly indifferent to outcomes, and interventionist creationism. Even a creator would leave unexplained, or arbitrarily complicate, the relation between nature’s internal capacities and a later intervention. The proposed teleology instead seeks immanent unity, but it has no formulated laws, empirical confirmation, or detailed mechanism.

The book’s force is consequently asymmetrical. Nagel presents his negative diagnosis with conviction, while his positive alternatives remain possibilities. Emergence, psychophysical monism, and teleology each face major obscurities. We do not know how protomental elements could compose a subject, how the rationality of a whole subject might be reduced, which laws could direct self-organization, or how such laws could be tested when only one history of life is known. Moral realism itself is not proved by defeating unduly restrictive naturalist arguments. Nagel acknowledges that subjectivism permits a more straightforward Darwinian story and that the realist interpretation must earn credibility through the quality of evaluative thought it makes possible.

The conclusion therefore recommends comparative inquiry rather than claiming a final refutation. Materialism, theism, emergentism, monism, and teleology must each be developed precisely enough to compare what they explain and what they leave brute. The concrete achievements of reductionism remain indispensable, but they do not guarantee a complete cosmology. The essay’s central demand is that subjective consciousness, reason’s claim to validity, and the possible objectivity of value be counted among the evidence, rather than downgraded because they resist the available framework. Nagel admits that the truth may exceed human cognitive powers. Still, he considers it premature to turn the limitations of present methods into limits of principle. The crucial distinction is clear: exposing the possible inadequacy of materialism does not prove teleology, but it does reopen the search for a richer conception of nature.