I. What Do We Mean by “Physical”?
II. Why Might We Think Reality Is Fundamentally Physical?
III. Reduction, Dependence, and Emergence
IV. What Kind of World Does Physicalism Give Us?
V. The Problem of Consciousness
VI. What Questions Does Physicalism Leave Open?
VII. How Might a Physicalist Respond?
VIII. Is the Physical Fundamental - or Simply Inescapable?
Conclusion: Is the Physical Enough?
Suggested Readings and Further Exploration
Why Were These Authors Chosen?
Essay Forty asked whether relations presuppose things. Essay Forty-One asked whether enduring things and their relations might themselves be better understood through process and becoming. Neither inquiry yielded the simple hierarchy we might have expected.
Things proved difficult to understand apart from the relations through which they are constituted and sustained. Relations seemed difficult to conceive without something related. Process explained change, continuity, and persistence in powerful ways, yet process itself appeared to depend upon temporal succession, distinguishable phases, and relations among what was, what is, and what becomes.
We were left with a provisional map:
Being ↔ Relation ↔ Becoming
But perhaps we have made the problem more complicated than it needs to be.
A philosopher inclined toward physicalism might ask why we should divide reality into metaphysical categories before asking what kind of reality the natural sciences already disclose. Why begin with substance, relation, or process rather than with the world investigated by physics, chemistry, biology, geology, and neuroscience?
Physics studies particles, fields, energy, spacetime, forces, and interactions. Chemistry studies atoms, molecules, bonds, reactions, and transformations. Biology studies cells, organisms, populations, ecosystems, inheritance, development, and evolution. Neuroscience studies brains whose physical activity accompanies perception, memory, emotion, decision, and consciousness.
Perhaps the realities we have been calling beings are physically organized systems.
Perhaps relations are physical interactions and dependencies.
Perhaps processes are physical transformations.
Perhaps becoming is simply the historical unfolding of physical systems into new configurations, capacities, and forms of organization.
If so, being, relation, and becoming may not identify three separate ontological ingredients at all. They may be three ways of describing what physical reality is and does.
That possibility should be taken seriously because physicalism offers something many metaphysical systems struggle to achieve: continuity. It proposes that the world does not repeatedly cross ontological boundaries as complexity increases. The star, the molecule, the cell, the brain, and the person all belong to one physically continuous reality, even though they may require very different levels of explanation.
The governing question therefore becomes:
Do we need a metaphysics of substance, relation, or becoming beyond the physical reality from which these phenomena arise?
Before answering, however, we must clarify what the word physical means.
I. What Do We Mean by “Physical”?
The word physical sounds straightforward until philosophy asks us to define it.
Historically, positions resembling contemporary physicalism were often called materialism. Ancient atomists imagined reality as atoms moving through the void. Later materialists likewise emphasized matter as the fundamental constituent of nature. Matter seemed extended, measurable, movable, and capable of entering causal relations.
But modern physics has complicated this picture. Fundamental reality is no longer easily imagined as a collection of tiny solid pieces of matter. Contemporary theories speak instead of particles, fields, energy, spacetime, symmetries, probabilities, interactions, and quantum states. What everyday language calls a “particle” may itself be described within field theory in ways that bear little resemblance to miniature billiard balls moving through empty space.
For this reason, philosophers increasingly use the broader term physicalism (e.g., or contemporary materialism or contemporary atomism).
In its broad contemporary forms, physicalism holds that everything concrete is physical or wholly dependent upon physical reality. The claim does not require everything to resemble matter as ordinary experience presents it. Whatever an adequate physics ultimately tells us about the basic character of the world, the physicalist maintains that no additional independently nonphysical domain is required to complete concrete reality.
Physicalism is therefore historically related to materialism without being identical to it.
It also needs to be distinguished from naturalism.
Naturalism generally holds that reality belongs to the natural order and should be understood without appeal to independently supernatural causes or realms. A naturalist may be a physicalist, but naturalism can be broader. One might believe that nature contains irreducible biological, mental, informational, or other features while still denying the need for supernatural explanation.
A further distinction is important between metaphysical naturalism and methodological naturalism. Methodological naturalism describes a practice of inquiry. Scientific investigation seeks explanations through publicly examinable natural processes rather than introducing supernatural causation whenever an event is unexplained. It asks what mechanisms, structures, conditions, regularities, and interactions can account for what occurs.
But a successful method does not by itself establish a metaphysical doctrine.
A neuroscientist can investigate the neural basis of memory without first deciding whether consciousness is entirely reducible to neural activity. A cosmologist can investigate the early universe without first establishing that the physical universe exhausts all reality. Methodological naturalism governs how investigation proceeds. Physicalism makes the stronger claim that the reality discovered through such investigation is ontologically sufficient.
That distinction prevents an easy circular argument. Physicalism cannot simply say that science discovers only physical causes because science looks only for physical causes, and therefore only physical causes exist.
Its case must be stronger than that.
The physicalist proposal becomes persuasive not because the word physical is obvious, but because the sciences appear repeatedly to uncover a causally and structurally connected world. The physicalist asks whether that continuity reflects something fundamental about reality itself.
II. Why Might We Think Reality Is Fundamentally Physical?
One of the strongest cases for physicalism comes not from a single philosophical proof but from a pattern of convergence.
Across the history of inquiry, phenomena once attributed to independent nonphysical agencies have repeatedly become intelligible through natural processes. Disease has become connected to pathogens, genetics, immune responses, cellular dysfunction, and environmental conditions. Heredity has become increasingly intelligible through chromosomes, DNA, molecular replication, gene regulation, and developmental systems. Lightning has become understandable through atmospheric electricity rather than divine anger. Planetary motion no longer requires celestial intelligences directing the heavens.
None of these discoveries proves physicalism. But together they create a powerful inductive expectation: when a phenomenon remains poorly understood, rather than add a new ontological domain continue investigating its physical and natural conditions.
The attraction of physicalism therefore rests partly upon explanatory continuity. Physical explanations do not appear as isolated successes. They connect across scales. Chemical reactions depend upon physical interactions. Biological processes depend upon chemistry. Neural activity depends upon biological organization. Behavior changes when those systems are physically altered. The sciences repeatedly encounter not several disconnected causal worlds but one deeply integrated order.
Consider anesthesia.
A patient enters an operating room conscious, speaking, remembering, anticipating, and responding. A chemical intervention alters the nervous system. Conscious awareness disappears. Later, as the anesthetic loses its effect and neural activity returns to characteristic patterns, conscious experience returns.
Whatever consciousness ultimately proves to be, its dependence upon physical conditions is difficult to ignore.
Similar relationships appear in sleep, brain injury, neurodegenerative disease, psychoactive drugs, electrical stimulation, seizures, sensory deprivation, and hormonal changes. Memory, mood, perception, decision-making, and personality can all be modified by changing the physical organization or functioning of the brain.
The physicalist sees more than correlation here. Physical intervention produces systematic changes in capacities ordinarily described as mental.
That pattern extends throughout nature. Alter molecular structure and chemical behavior changes. Alter gene expression and development can change. Change atmospheric concentrations and climate systems respond. Modify neural circuitry and behavior can be affected.
Physicalism interprets this convergence ontologically: perhaps the reason the sciences connect so effectively across scales is that the realities they investigate belong to one physically continuous world.
This is where the idea of causal closure becomes important.
Many physicalists argue that physical events appear to have sufficient physical causes. A muscle contracts because of electrochemical and physiological processes. A neuron fires because membrane potentials, ion channels, neurotransmitters, and prior neural activity create the relevant conditions. A falling object changes velocity because physical forces act upon it.
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If the physical causal story is sufficient, an independently nonphysical cause faces a difficult problem.
Suppose a person raises an arm because of an immaterial mental cause. If the neural and muscular processes already constitute a sufficient physical causal sequence, what additional work does the immaterial cause perform? If it alters the physical sequence, then the physical account was not causally sufficient. If it does not alter the sequence, its causal contribution becomes difficult to identify.
This is sometimes connected with the problem of causal overdetermination. If both a complete physical cause and a distinct nonphysical cause independently produce the same event, why should ordinary physical actions routinely require two sufficient causes?
Causal closure is not a laboratory measurement that settles metaphysics by itself. Its philosophical strength lies in the broader continuity of successful physical explanation.
The physicalist therefore asks a question of ontological economy:
If physical reality already performs the causal work, what explanatory work requires an additional nonphysical reality?
That is a serious challenge.
And it shifts the burden of argument. Instead of asking physicalism to explain why everything should be physical, the physicalist may ask advocates of additional ontological domains to identify where physical explanation demonstrably fails because something nonphysical is required.
Still, even if everything depends upon physical reality, another question remains.
Must everything therefore be reduced to physics?
III. Reduction, Dependence, and Emergence
Physicalism may be understood as a contemporary successor to substance metaphysics - one in which the role once played by substance is increasingly generalized into the physical order itself.
Physicalism is often caricatured as the claim that a person is “nothing but atoms.” But contemporary physicalism can be considerably more sophisticated. It can affirm one physical order of reality while also recognizing that physical reality develops through multiple levels of organization and must often be understood through multiple levels of explanation.
This creates a modern version of an old metaphysical problem. If one physical order underlies everything else, how should we understand the increasingly complex realities that arise within it? Three different hierarchies can easily be confused.
This distinction matters because three different hierarchies can easily be confused.
1 - The first is a hierarchy of physical organization. Physical reality appears at many scales and in many arrangements. Fundamental physical constituents participate in atoms; atoms in molecules; molecules in cells; cells in organisms; organisms in nervous systems, ecosystems, and societies. These are not necessarily different kinds of being. They may instead be increasingly complex organizations of one physically continuous reality.
2 - The second is a hierarchy of explanation. Different sciences attend to different levels because the questions being asked differ. Physics explains one range of structures and interactions. Chemistry explains molecular composition, bonding, and reaction. Biology explains metabolism, inheritance, regulation, development, and adaptation. Neuroscience investigates neural organization and activity. Psychology asks questions about perception, cognition, memory, motivation, and behavior.
A living cell is physically constituted, yet knowing only the masses, charges, and positions of its constituent particles does not by itself provide an adequate biological explanation of membrane transport, metabolism, reproduction, signaling, regulation, or agential consciousness. The physical facts remain indispensable, but biological organization makes additional explanatory concepts necessary.
Something similar occurs with a computer program. A program running on a machine depends completely upon physical hardware. Every operation requires physical states within processors, memory, circuitry, and storage. Yet a description of voltage changes across every transistor may tell us remarkably little about what the program is calculating. The physical description is true, but another level of explanation becomes necessary because the organized system is doing something that cannot be usefully described in transistor language alone.
This gives us a central principle:
One ontology need not require one level of explanation.
A physicalist can therefore maintain that reality is ontologically continuous while allowing explanatory plurality. Physics need not replace chemistry, chemistry need not replace biology, and biology need not automatically replace psychology merely because the higher-level phenomena depend upon lower-level physical organization.
3 - he third hierarchy concerns emergent capacities. As physical systems become differently organized, new structures, functions, and capacities may appear. These capacities are not necessarily new substances added to the universe. They may arise because organization changes what the system as a whole can do.
These three hierarchies can therefore be distinguished as:
levels of physical organization → levels of explanation → levels of emergent capacity
The distinction helps clarify an important difference between ontological dependence and explanatory reduction. A higher-level phenomenon may depend completely upon physical reality without therefore being adequately explained in the vocabulary of fundamental physics.
A reductive physicalist may argue that higher-level phenomena are ultimately identical with, or fully reducible to, lower-level physical states. A nonreductive physicalist may instead maintain that higher-level realities possess legitimate explanatory descriptions of their own while remaining wholly dependent upon physical organization.
One way philosophers have characterized such dependence is through supervenience. In simplified form, supervenience means that there cannot be a difference at the higher level without some corresponding difference in the underlying physical facts. If two systems were physically identical in every relevant respect, a physicalist would ordinarily deny that one could differ mentally, biologically, or behaviorally while nothing physical differed between them.
Supervenience therefore expresses dependence, but it does not by itself explain how higher-level organization arises or why a new organization acquires capacities not usefully attributable to its components considered separately.
That brings us to emergence.
Emergence becomes philosophically important when the interaction and organization of physical components produce stable patterns, functions, or capacities that belong to the system as organized rather than to its constituents in isolation. Simply collecting more objects together is not enough. A pile of identical stones does not thereby acquire a radically new kind of behavior merely because the pile is larger.
But some forms of organization do matter profoundly.
Consider superconductivity. Under appropriate conditions, certain materials undergo transitions in which electrical resistance can fall dramatically and collective quantum behavior appears. No single constituent considered by itself is superconducting in the way the organized material is. The phenomenon belongs to the coordinated behavior of the system.
Or consider protein folding. A protein begins as a chain of amino acids, but its biological activity often depends upon the three-dimensional structure that develops through interactions among its constituent parts and surrounding environment. The resulting form is not a new substance introduced from outside the molecule. It emerges through physical organization. Yet once folded, the protein can possess functional capacities that make little sense when attributed to an isolated amino acid.
These examples clarify the third hierarchy.
New organization can produce new capacity.
And this exposes an important distinction:
Novelty need not require ontological addition.
A genuinely new structure, function, or capacity may appear without a new kind of substance entering the universe. Something new may happen because physical reality has become differently organized.
This is one of the strongest resources available to contemporary physicalism. It allows the physicalist to acknowledge real novelty without abandoning ontological continuity.
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Additionally, philosophers sometimes distinguish weak emergence from strong emergence. Weak emergence describes higher-level phenomena that arise entirely from lower-level physical interactions, even when the resulting behavior is difficult or impossible to predict without allowing the system to unfold. The novelty belongs to organization, complexity, and interaction rather than to the introduction of a fundamentally new kind of reality.
Strong emergence makes a more demanding claim. On strong emergentist accounts, higher-level systems may possess genuinely new causal powers or properties that cannot in principle be reduced to or derived from the lower-level physical facts alone.
Physicalism is generally comfortable with weak emergence because weak emergence preserves physical continuity. Strong emergence creates greater difficulty. If a higher-level property introduces genuinely new causal powers not determined by the underlying physical reality, the physicalist must explain in what sense the higher level remains fully physical.
The tension arises because physicalism wants to preserve two insights at once.
It wants to maintain ontological continuity: reality does not need to acquire a new kind of being whenever complexity increases.
But it also wants to acknowledge organizational and explanatory plurality: increasingly complex systems can display forms of structure, behavior, and capacity that require new explanatory languages.
The strongest physicalist proposal is therefore not that nothing genuinely new ever happens. It is that:
new organization can be genuinely new without being made of a new kind of reality.
This allows biological organisms, ecosystems, nervous systems, technologies, languages, social systems, and perhaps consciousness itself to arise within one physically continuous world without requiring us to suppose that a new ontological substance appears at each stage.
The resulting picture can be summarized through three coordinated claims:
Ontological continuity - one physical reality.Organizational plurality - many levels and forms of physical organization.Explanatory plurality - many legitimate levels of description and explanation.
Emergence then describes what may happen as organization changes: new capacities become possible.
This is why reductionism and physicalism should not be treated as synonyms. Something may be wholly physical without being adequately understood at the level of fundamental physics alone.
A physicalist can therefore accept many levels of organization, many levels of explanation, and genuine novelty in capacity without multiplying fundamental kinds of being.
The world, on this account, may be plural in organization and explanation while remaining continuous in being.
IV. What Kind of World Does Physicalism Give Us?
A physicalist universe need not resemble the cold mechanical world sometimes associated with older forms of materialism. It can be dynamic, historical, layered, unstable, generative in its outcomes, and astonishingly complex.
Stars form from gravitational collapse. Nuclear fusion produces heavier elements. Stellar explosions distribute those elements into surrounding space. Planetary systems develop from later generations of matter. Chemistry becomes increasingly complex under appropriate conditions. On at least one planet, self-maintaining systems arise, reproduce, vary, and evolve.
Over immense spans of time, physical reality develops forms of organization that did not previously exist except as latent potentiality.
We might describe one trajectory as:
physical reality → complex organization → life → nervous systems → consciousness → culture
This should not be mistaken for an inevitable ladder of progress or an orthogenetic picture in which evolution is internally directed toward greater complexity, life, consciousness, or mind. Most matter never becomes living, and evolution possesses no predetermined obligation to produce minds. Physical processes generate dissolution and destruction as readily as increasing complexity. Stars collapse. Species vanish. Ecosystems fail. Biological lineages terminate.
The point is not that physical reality naturally moves toward perfection. The point is that a physical universe can produce history. This matters because physicalism can now answer several problems raised in Essays Forty and Forty-One without abandoning its own framework.
Physicalism need not deny being. Beings can be relatively stable physical organizations.
It need not deny relation. Physical reality is filled with interactions, correlations, dependencies, structural constraints, and mutually conditioning systems.
It need not deny process. Physical systems transform across multiple temporal scales.
It need not deny becoming. New states, structures, capacities, and organizations arise through physical history.
It need not deny emergence. Higher-level forms can arise through the organized activity of physical constituents.
The physicalist may therefore challenge one of the assumptions that has accompanied our inquiry.
Perhaps the metaphysical mistake lies in turning useful categories of description into separate ingredients of reality.
“Relation” may name the interactions and dependencies through which those“Being” may name the relatively stable organizations we identify.
organizations exist and affect one another.
“Becoming” may name their transformations through time.
Physicalism does not necessarily need to choose which of these is ontologically prior because it can interpret all three as aspects of one physically continuous reality.
Our formulation
Being ↔ Relation ↔ Becoming
may therefore describe something real without identifying separate metaphysical primitives.
Perhaps all three belong within:
Physical Reality
This is a stronger challenge than the crude statement that “everything is matter.”
It proposes instead that one reality can display multiple forms of organization without requiring multiple ontological substances.
A crystal, a bacterium, a brain, and a human society are radically different kinds of organized realities. Their explanations occur at different scales. Yet the physicalist can maintain that no ontological fracture separates them.
Physical continuity does not require explanatory uniformity.
This is perhaps one of physicalism's most important insights:
The universe need not be metaphysically supplemented each time a new form of organization appears.
What appears astonishing may not be that physical reality explains too little. It may be what physically organized reality proves capable of becoming.
Yet one phenomenon continues to create unusual pressure.
Some physical systems do not merely respond to their environments.
They appear to experience them.
V. The Problem of Consciousness
Few observations seem more secure than the dependence of ordinary human consciousness upon the brain. Damage particular neural systems and capacities disappear. Modify brain chemistry and mood or perception can change. Interrupt normal neural integration and consciousness can diminish or vanish. Restore the relevant physiological conditions and awareness may return.
For the physicalist, these patterns are powerful evidence against the idea that the mind is an entirely independent substance merely operating the brain from elsewhere.
Mental life appears profoundly embodied.
Yet physical dependence is not automatically the same thing as explanatory completeness.
Imagine that neuroscience eventually produces an extraordinarily detailed account of what occurs when a person sees the proverbial "red apple." We understand the wavelengths of reflected light, retinal processing, signal transmission, neural pathways, cortical integration, memory association, attention, verbal report, and behavioral response. We can perhaps predict when the person will say, “I see a red apple.”
A remarkable amount has been explained.
But a philosopher may still ask why any of this is accompanied by the experience of seeing red.
Why does neural processing feel like anything from the inside?
This is part of what philosophers call the explanatory gap between third-person descriptions of physical processes and first-person subjective experience.
The concept of qualia is often used to name the felt character of experience. Pain does not merely transmit information about bodily damage; pain hurts. Coffee tastes like something. Music is heard from somewhere within experience. Colors possess phenomenal character.
David Chalmers famously described the question of why physical processing is accompanied by subjective experience as the hard problem of consciousness.
But the physicalist need not concede that an explanatory gap is an ontological gap.
This is where physicalism deserves a stronger response than it is sometimes given.
Human beings routinely encounter different levels of description that initially appear difficult to connect. Temperature as experienced does not resemble the statistical behavior of molecular motion. Lightning does not visually resemble the mathematical description of an electrical discharge. The hereditary traits of an organism do not resemble the molecular structures through which genetic information is transmitted.
In such cases, scientific explanation connects descriptions that ordinary intuition would never have identified as belonging to one process.
Consciousness may be different. First-person experience presents difficulties that temperature and lightning do not. But the physicalist can still insist upon an important principle:
The fact that first-person experience and third-person neuroscience employ radically different descriptions does not yet establish that they describe two fundamentally different realities.
The apparent gap may reflect incomplete science.
It may reflect conceptual limitations.
It may arise because subjective and objective descriptions necessarily approach the same reality from different perspectives.
Or it may indeed reveal something physicalism cannot explain.
At present, the alternatives remain contested.
This forces us to distinguish two claims carefully.
Consciousness appears strongly dependent upon physical reality.
Whether physical reality exhaustively explains consciousness is a further question.
The physicalist can therefore resist an easy inference from mystery to metaphysics. What has not yet been physically explained has not thereby been shown to be physically inexplicable.
But physicalism cannot simply assume victory either. The historical success of physical explanation elsewhere does not logically guarantee that every remaining problem will yield in the same way.
So consciousness leaves us with a genuine uncertainty.
Does the explanatory gap reveal unfinished science, a limitation of our conceptual frameworks, or a real ontological divide?
For now, the question remains open.
VI. What Questions Does Physicalism Leave Open?
The most basic difficulty facing physicalism sounds deceptively simple.
What does physical mean?
If physicalism means that everything is composed of what present physics recognizes, the thesis may be too restrictive. Scientific theories change. Concepts once regarded as fundamental are revised. New theoretical entities and structures are introduced. A metaphysics tied too closely to one historical stage of physics risks becoming obsolete as science develops.
But if physicalism means that everything consists of whatever a perfected future physics will ultimately recognize, another problem appears.
We do not yet know what such a physics-of-the-future will contain.
This difficulty is commonly associated with Hempel's dilemma. Define the physical by present physics and the definition is likely incomplete. Define it by ideal future physics and the content of the thesis becomes difficult to specify in advance.
The dilemma does not refute physicalism, but it exposes a boundary problem.
The word physical cannot simply mean “whatever ultimately exists,” because then physicalism would become the trivial statement that everything real is real.
The physicalist needs some substantive continuity between physical theory, empirical inquiry, causal organization, and the ontology being proposed.
A second difficulty concerns higher-level explanation.
Suppose mental states, biological functions, and social structures depend entirely upon physical reality. If they nevertheless possess genuine causal significance, how does their causal role relate to that of the underlying physical processes?
This problem becomes especially sharp for nonreductive physicalism.
If a person's decision causes an arm to move, and the neural state underlying that decision already provides a sufficient physical cause of the movement, what independent causal role remains for the higher-level mental state?
This is sometimes called the causal exclusion problem.
If the mental cause is identical with, or reducible to, the physical cause, reduction begins to return.
If the mental cause is genuinely distinct but produces the same physical effect, causal overdetermination threatens.
If it produces no additional physical effect, its causal efficacy becomes unclear.
Nonreductive physicalism therefore cannot simply declare both physical sufficiency and robust higher-level causation without explaining their relationship.
Emergence raises a related difficulty.
The stronger emergence becomes, the more explanatory independence higher-level phenomena seem to possess. But the more independent they become, the harder it is to explain why physicalism remains complete.
The weaker emergence becomes, the easier it is to preserve physicalism, but the harder it becomes to say what philosophical work the term emergence is accomplishing beyond describing complicated physical organization.
There are other questions at the edges of the position: mathematical truths, logical relations, meanings, normativity, value, and abstract objects may all complicate broad definitions of physicalism. But these questions need not be settled here.
The central problem is already sufficient.
Physicalism must explain physical dependence strongly enough to say something substantive without defining the physical so broadly that nothing could count against it.
VII. How Might a Physicalist Respond?
A sophisticated physicalist has several strong replies available.
First, physicalism does not require present physics to be complete. Science is corrigible by design (capable of being corrected, set right, improved, or reformed). A metaphysical position informed by science need not identify reality with every entity listed in a current textbook. The physicalist can instead appeal to continuity with the causally and structurally integrated world investigated by the physical sciences.
Second, physicalism need not require all legitimate explanations to occur at the lowest possible level.
A neuroscientist explaining memory does not need to rewrite the explanation in the language of particle physics. A biologist explaining natural selection does not need to track every elementary particle within a population. A materials scientist explaining superconductivity can work with collective properties that would be invisible in a description focused only upon isolated constituents.
Different scales require different explanatory vocabularies.
Physical grounding does not imply explanatory replacement.
Third, the causal exclusion problem may itself be partly generated by treating levels of description as though they were competing causes. A person's decision and the neural processes realizing that decision may not be two independent events fighting for causal ownership of one bodily movement. They may be descriptions of one causally integrated occurrence at different explanatory levels.
If so, higher-level causal explanation need not introduce a second causal force.
The physicalist can make a similar point about emergence.
A biological function is not a ghost added to molecules. It is what physically organized molecules are doing within a particular system. A higher-level constraint need not arrive from outside the physical world; it can arise from the organization of that world itself.
This permits physicalism to remain pluralistic about explanation while monistic about concrete ontology.
Fourth, consciousness need not overturn the position merely because current explanations remain incomplete.
The physicalist can reasonably insist:
Do not confuse what has not yet been physically explained with what cannot be physically explained.
History provides ample reason for caution here. Human intuitions about what matter “could never do” have repeatedly underestimated what organized physical systems can accomplish. Life once appeared to require a special vital force. Complex biological adaptation once appeared impossible without direct design. Mental capacities once seemed radically detached from bodily mechanisms.
Again, none of these historical developments proves that consciousness will eventually receive a complete physical explanation. But they weaken arguments that proceed primarily from incredulity.
Finally, the physicalist can invoke a principle of ontological economy.
Before adding another fundamental kind of reality, identify the work it must perform.
What phenomenon requires it?
How does it interact with the physical world?
What observations would distinguish a universe containing it from one that does not?
Why multiply ontological categories if a physically continuous account remains viable?
The burden of proof need not fall entirely upon physicalism. The physicalist can reasonably ask those who propose something beyond the physical to show why it is required. This is perhaps the strongest version of the position. Physicalism need not claim that every question has been answered. It claims that the existence of unanswered questions has not yet established the need for another kind of reality.
VIII. Is the Physical Fundamental - or Simply Inescapable?
Physicalism has forced us to recognize the extraordinary depth of physical dependence.
Every concrete reality we investigate empirically appears physically embodied, physically realized, or physically conditioned. Organisms require material structures and energy. Brains require biological systems. Speech requires bodies or physical media. Institutions require embodied persons, practices, artifacts, technologies, and continuing forms of organization.
Nothing in ordinary empirical experience appears to float free of physical conditions.
That is an important result.
But dependence and fundamentality remain different claims.
Essay Forty taught us that relations requiring relata does not automatically prove the ontological priority of substance. Essay Forty-One showed that the explanatory importance of process does not automatically prove the ontological priority of becoming.
Physicalism now confronts a parallel distinction.
One proposition is:
Every concrete reality we investigate appears physically realized or physically conditioned.
Another is:
Everything that exists is fundamentally physical.
The first is strongly supported by empirical inquiry.
The second remains a metaphysical interpretation of that evidence.
This distinction should not be used to make physicalism seem weaker than it is. Physicalism may possess extraordinary empirical support compared with many rival metaphysical proposals. The point is simply that empirical indispensability and ontological exhaustiveness are not identical.
Physicalism may nevertheless respond that the distinction itself is misleading.
Perhaps there is no need to imagine “the physical” as a foundational layer lying beneath everything else. If reality is one continuous natural world, then physicality may characterize that world across its many scales and organizations.
Atoms are physical.
Cells are physical.
Brains are physical.
Persons are physically embodied.
Their differences are immense, but difference need not imply ontological separation.
On this account, physicalism becomes less a doctrine of reduction than a doctrine of ontological continuity. Reality can possess many levels without containing many fundamentally different kinds of concrete being.
This may be physicalism's deepest attraction. It promises one world without requiring one vocabulary. Physics, chemistry, biology, neuroscience, psychology, sociology, and history can all describe genuinely important aspects of reality without implying that each discipline studies a different ontological realm.
The world may be plural in organization while continuous in being.
If so, our earlier search for a single primitive may itself have been too restrictive.
Perhaps being, relation, and becoming are not rival foundations.
Perhaps they are dimensions of physically organized reality encountered under different descriptions.
The question then becomes subtler than whether the physical exists.
The physical appears unavoidable.
The question is whether it is exhaustive.
Conclusion: Is the Physical Enough?
We began by asking whether the metaphysical categories developed through our previous inquiries might be doing more work than reality requires.
Perhaps being, relation, and becoming are not competing ontological foundations. Perhaps they describe different aspects of one physically continuous world.
Physicalism gives us substantial reasons to entertain that possibility.
Its strength lies partly in its continuity with the natural sciences and partly in the cumulative integration those sciences disclose. The same universe investigated by cosmology produces stars and planets. Stellar history produces the elements later incorporated into chemistry. Chemistry participates in the formation of living systems. Some organisms develop nervous systems. Some nervous systems eventually become capable of memory, imagination, language, self-reflection, mathematics, art, and philosophical inquiry.
Nothing in this history obviously requires reality to divide itself into separate ontological realms.
Physicalism can therefore make a bold proposal:
Reality is physical, and everything else is what physical reality becomes.
- This proposal does not require a static universe.
- It does not require the denial of relation.
- It does not require the denial of process.
- It does not require the denial of emergence.
- It does not even require the elimination of higher-level explanation.
Its deepest claim is instead that one physically continuous reality may be sufficient to support many levels of organization without requiring many kinds of fundamental being.
That is a philosophically formidable possibility.
It also changes the pressure upon our own inquiry.
Perhaps being, relation, and becoming are not ingredients from which reality is assembled.
Perhaps they are ways of recognizing the stability, interdependence, and history of physical systems.
If that is so, the metaphysical question does not disappear.
It changes.
We must ask whether the physical dependence of everything we empirically encounter establishes that physical reality is ontologically exhaustive.
And here consciousness remains especially difficult.
A universe that once contained no known reflective organisms now contains beings for whom reality is experienced from somewhere. There is pain and pleasure, color and sound, memory and anticipation, imagination and fear. The world is not merely processed by these beings. It appears to them.
We can alter experience by altering brains. We can identify neural activity associated with perception. We can increasingly map the physical conditions under which consciousness changes, disappears, and returns. But whether those achievements finally explain why there is something it is like to experience reality remains unsettled.
The physicalist can reasonably ask us to wait. Science is unfinished. Explanatory gaps are not automatically ontological gaps.
Yet another philosopher may reverse the question.
Instead of asking how physical reality eventually gives rise to mind, perhaps we should ask whether mind, consciousness, or experience belongs more deeply to reality than physicalism allows.
We have asked whether mind can arise entirely from the physical.
The direction of explanation can now be reversed.
What if reality is mind?
And once again, we begin somewhere else.
Papineau, David. Philosophical Naturalism. Oxford: Blackwell, 1993.
Stoljar, Daniel. Physicalism. London: Routledge, 2010.
Stoljar, Daniel. “Physicalism.” The Stanford Encyclopedia of Philosophy. First published February 13, 2001; substantive revision May 25, 2021.
Physicalism - Stanford Encyclopedia of Philosophy
Papineau, David. “Naturalism.” The Stanford Encyclopedia of Philosophy.
Naturalism - Stanford Encyclopedia of Philosophy
Mind, Reduction, and Physical Dependence
Kim, Jaegwon. Physicalism, or Something Near Enough. Princeton, NJ: Princeton University Press, 2005.
Smart, J. J. C. “Sensations and Brain Processes.” The Philosophical Review 68, no. 2 (1959): 141-156.
Consciousness and the Limits of Physical Explanation
Nagel, Thomas. “What Is It Like to Be a Bat?” The Philosophical Review 83, no. 4 (1974): 435-450.
Chalmers, David J. The Conscious Mind: In Search of a Fundamental Theory. New York: Oxford University Press, 1996.
Emergence and Higher-Level Reality
Kim, Jaegwon. Mind in a Physical World: An Essay on the Mind-Body Problem and Mental Causation. Cambridge, MA: MIT Press, 1998.
Bedau, Mark A., and Paul Humphreys, eds. Emergence: Contemporary Readings in Philosophy and Science. Cambridge, MA: MIT Press, 2008.
David Papineau is important because physicalism becomes considerably more persuasive when placed within the wider history of philosophical naturalism. Naturalism helps explain why physicalism is not merely a speculative preference for “matter” but emerges from confidence in the explanatory and causal continuity of the sciences. The contemporary naturalist argument is closely connected with the historical decline of independent vital and mental forces and the growing importance of the causal completeness of the physical world.
Jaegwon Kim is particularly important for the tensions within nonreductive physicalism. His work on mental causation and causal exclusion presses the question raised in this essay: if a physical event already possesses a sufficient physical cause, what causal work remains for a distinct higher-level mental cause? Physicalism, or Something Near Enough is valuable precisely because Kim is neither simply dismissing physicalism nor presenting it as philosophically effortless. He treats mental causation and consciousness as two of its principal difficulties.
J. J. C. Smart represents an influential twentieth-century form of mind-brain physicalism. His work is useful because it displays the attraction of identifying apparently mental phenomena with physical brain processes rather than multiplying ontological categories. Even where later physicalists reject straightforward identity theories, the pressure Smart articulated remains: if mental events are causally embedded within the physical world, why posit an additional mental substance?
The selections from Thomas Nagel and David Chalmers were chosen not because they represent physicalism's own strongest advocates, but because they formulate the challenge from consciousness with unusual clarity. Nagel's famous question about what it is like to be a bat emphasizes the subjective character of experience and the apparent difficulty of capturing that character through an exclusively objective description. His 1974 essay became one of the most influential formulations of the problem.
David Chalmers's The Conscious Mind develops the challenge more systematically. Chalmers distinguishes questions about cognitive function and information processing from the deeper question of why physical processes should be accompanied by subjective experience at all. His book is especially relevant to Essay Forty-Two because it allows us to ask whether the explanatory gap between physical description and consciousness is merely temporary or points toward a more fundamental limitation of strict physicalism.
Finally, the readings on emergence were included because contemporary physicalism becomes much more interesting once we stop assuming that physical dependence requires simple reduction. Emergentist approaches explore how higher-level organization, pattern, function, and causal structure may arise from physical systems without necessarily constituting a separate kind of substance. This is essential to the form of physicalism encountered in Essay Forty-Two. The question is not merely whether reality is physical, but whether one physically continuous reality can genuinely produce many levels of organization without requiring many fundamentally different kinds of being.
Taken together, these readings allow physicalism to appear in its strongest contemporary form. They move us away from the image of a universe composed simply of inert matter and toward a much richer possibility: a physically continuous world capable of structure, interaction, emergence, life, consciousness, and history.
The question that remains is correspondingly sharper:
Does physical dependence ultimately establish physical exhaustiveness?
That, rather than the older question of whether “matter exists,” is the problem Essay Forty-Two leaves open.
The change in terminology reflects a change in our understanding of the physical world.
| Concept | Historical Context | Basic Emphasis |
|---|---|---|
| Materialism | Antiquity through the nineteenth century | Reality is fundamentally composed of matter and its motions or interactions. |
| Physicalism | Twentieth century to the present | Everything concrete is physical, or depends upon the realities, structures, and laws ultimately described by physics. |
Classical materialism could often imagine reality as composed of material bodies or particles moving through space. Modern physics has made that picture considerably more complicated. Fields, energy, spacetime, quantum states, and other physical structures do not resemble the solid material objects of ordinary experience.
For this reason, physicalism became the more useful philosophical term. It allows the ontology to remain open to whatever an adequate physics ultimately discovers rather than committing metaphysics to an older conception of matter.
In this sense:
Materialism may be understood as the historical ancestor of contemporary physicalism.
The central intuition remains similar - no independently nonphysical realm is required to complete concrete reality - while the meaning of physical has expanded along with science.
Why Physicalism Is Not Simply Atomism
Physicalism should also be distinguished from atomism.
Atomism proposes that reality can ultimately be analyzed into discrete fundamental units. Ancient atomists imagined indivisible atoms moving through the void, and later forms of atomistic thinking likewise sought basic constituents beneath complex things.
Physicalism makes no such specific commitment.
If fundamental physics ultimately describes reality through particles, a physicalist can accept particles. If it instead requires fields, spacetime structures, quantum states, or some combination not easily understood as discrete objects, physicalism can accommodate those as well.
Thus:
This flexibility is one reason physicalism has become more prominent than classical materialism within contemporary metaphysics.
It also creates an important difficulty. If physicalism means “whatever a completed physics eventually tells us exists,” how can we presently define what counts as physical?
That problem is commonly associated with Hempel’s Dilemma, and it reminds us that even physicalism’s central term remains philosophically open.
