Conclusion: Can Reality Be One and Genuinely Many?
The preceding essays have repeatedly changed the point from which metaphysical inquiry begins. We began with things and asked whether relations presuppose beings capable of standing in relation. We then reversed the question and considered whether enduring things might themselves arise within processes of becoming. Physicalism asked whether things, processes, organisms, minds, and worlds might ultimately belong to one physically continuous reality. Idealism and consciousness-first metaphysics reversed the explanatory direction again, asking whether experience can really be treated as a late arrival within a reality first conceived as fundamentally nonexperiential.
Each alternative shifted the starting point. Each made something newly visible. Each also created new explanatory burdens.
Yet another question has been forming beneath these disagreements. Metaphysics repeatedly distinguishes things from relations, being from becoming, physical from mental, object from subject, world from experience. Such distinctions are indispensable to thought. But does every distinction we discover within reality identify a fundamental division of reality itself?
The question becomes especially important after physicalism and idealism. Both can be monistic while disagreeing profoundly about what is fundamental. One may interpret mentality within a physical reality; another may interpret physical reality within mind or experience. Their disagreement therefore reveals that saying reality is one does not yet tell us what that reality is.
Perhaps, then, we have reached a different question. Rather than choosing immediately between physical and mental, substance and process, subject and object, we might ask whether these differences belong within some deeper unity.
Few philosophers pursued that possibility more rigorously than Baruch Spinoza. His metaphysics proposed one substance - God or Nature - within which the multiplicity of finite things and the apparent division between thought and extension must be understood. Later monisms have taken different routes, from physical and idealist monisms to neutral and priority monism. Their answers differ, but they share a question:
How much metaphysical division does the diversity of reality actually require?
To answer it, we must first clarify an apparently simple proposition.
What does it mean to say that reality is one?
I. What Does It Mean to Say Reality Is One?
One what?
One substance? One kind of reality? One fundamental ground? One concrete whole? One metaphysically basic entity?
These are importantly different claims.
Substance monism holds that there is ultimately one substance. Spinoza provides the great historical example. Kind monism maintains that everything belongs ultimately to one fundamental kind of reality. Physicalism and idealism can both take this form despite disagreeing about whether that reality is physical or mental. Priority monism makes a different claim: many things may exist, while the whole to which they belong is metaphysically more fundamental than its parts.
We can therefore be monists about one question while accepting considerable plurality elsewhere. A physicalist need not believe that only one physical object exists. A priority monist need not deny the reality of stars, organisms, or persons. And a substance monist need not claim that every distinction within the one substance is illusory.
This gives us the first necessary caution:
Unity is not uniformity.
A living organism is one organism while containing differentiated organs, tissues, cells, and processes. A language remains one language despite differences of vocabulary, grammar, dialect, and use. Such examples do not prove metaphysical monism, but they show that unity and differentiation are conceptually compatible.
Monism therefore need not begin by denying the many.
It asks instead about the metaphysical status of the many. Are individual things ultimately self-grounding realities? Do apparently different kinds of existence require different ontological foundations? Or can genuine differences belong within one more fundamental reality?
The word one cannot answer these questions.
It names the problem.
II. Why Has Philosophy Sought Unity?
The search for unity has repeatedly appeared in metaphysics because plurality carries explanatory costs of its own.
If reality contains several fundamentally independent kinds of being, philosophy must explain how they belong to a common world. If mind and matter are separate substances, how do they interact? If independently existing substances constitute reality, what accounts for their relations and common order? If subject and object occupy radically different ontological domains, how does knowledge connect them?
Monism offers a powerful possibility: perhaps what appears to require bridges between realities can instead be understood as differentiation within reality.
There is also an attraction to explanatory economy. Philosophy, like other forms of inquiry, often prefers an account capable of explaining more while assuming less. Parsimony (extremely thrift, frugal, avoiding waste, economical) does not prove monism - the simplest ontology is not necessarily the true one - but unnecessary multiplication of fundamental entities demands justification.
Yet the search for unity carries an opposite danger. A theory may become simple because it has explained diversity, or because it has eliminated diversity by definition. Saying that everything is really matter, mind, spirit, information, or one substance may reveal a deep metaphysical unity. It may also merely relocate the question of how the world's extraordinary differentiation arises.
Monism therefore stands between two risks.
Too much separation leaves reality fragmented into domains whose relations become mysterious.
Too much unity makes difference difficult to preserve.
The challenge is not simply to reduce reality to one.
It is to show how the one can contain the many.
Spinoza made that challenge central to one of philosophy's most ambitious metaphysical systems.
III. Spinoza and the One Substance
Spinoza begins with an unusually demanding definition of substance: that which exists in itself and is conceived through itself. A genuine substance cannot depend upon something more fundamental for either its existence or its intelligibility.
Under such a definition, ordinary objects do not qualify. A tree depends upon soil, water, sunlight, biological inheritance, and an environment. A human being depends upon a body, history, world, and innumerable conditions not contained within the individual. Even planets and stars belong within wider systems of dependence.
Spinoza's conclusion is radical. There cannot ultimately be a plurality of independent substances. There is one infinite substance, which he identifies as God or Nature - Deus sive Natura.
This should not be reduced to the simple claim that God is identical with the physical universe. Spinoza's God is not a supernatural creator standing outside nature and acting upon it from elsewhere. Neither, however, is his infinite substance merely the collection of physical objects visible to us. God or Nature names the infinite, self-caused reality within which everything finite exists.
This is a metaphysics of immanence. Reality does not require a second ontological realm outside itself to account for its existence and order.
Finite things are therefore not substances in the ultimate sense. They are modes - determinate ways in which the one substance exists. Their dependence does not make them nonexistent. It means that they do not possess the self-sufficient being Spinoza reserves for substance itself.
Spinoza also binds unity to necessity. Everything follows from the nature of God or Nature rather than from an external act of arbitrary choice. Reality could not simply have been otherwise in the way a creator might have chosen another possible world. This necessitarian dimension gives Spinoza's monism extraordinary explanatory unity, but it will also raise difficult questions concerning contingency, freedom, and novelty.
For now, however, Spinoza has supplied a powerful answer to our initial question. Reality can be fundamentally one while containing innumerable finite modes.
But his most striking demonstration of this unity appears in the relation between mind and body.
IV. Thought and Extension Within One Reality
Mind and body appear profoundly different. Thoughts do not seem to occupy space in the way bodies do. Bodies possess extension, mass, location, and movement, while ideas, memories, intentions, and sensations possess a different character.
If these differences identify separate substances, however, the problem of interaction immediately arises. How can an unextended mind causally affect an extended body; conversely, how does the body affect the mind?
Spinoza changes the structure of the problem.
The one substance possesses infinitely many attributes, of which human beings know thought and extension. Mind and body therefore do not belong to two independent substances that somehow have to communicate. They belong within one reality understood under different attributes.
This produces what is commonly described as Spinoza's psychophysical parallelism. The order and connection of ideas corresponds to the order and connection of things because thought and bodily extension express the same underlying reality rather than two disconnected worlds.
The point is metaphysically significant even apart from accepting Spinoza's entire system. A difference between mental and physical characteristics need not automatically establish two independent realities.
Consider a person listening to music. The event can be described acoustically, neurologically, physiologically, psychologically, phenomenologically, and biographically. These descriptions are not interchangeable. A neural description does not reproduce what the melody sounds like, while a report of the listener's experience does not replace the physical account of sound transmission. In sum, the plurality of descriptions do not by themselves demonstrate a plurality of worlds.
Spinoza therefore invites a question that reaches beyond his own philosophy:
Might some metaphysical problems arise because we mistake different expressions or descriptions of reality for different realities?
This does not establish that mind and matter are one in precisely Spinoza's sense. It does, however, loosen the assumption that genuine difference requires ontological separation.
And that immediately returns us to the problem every serious monism must face.
If reality is one, what are all these different things?
V. The One and the Many
Reality does not present itself as undifferentiated unity. We encounter stars and bacteria, oceans and memories, organisms and societies, persons with distinct histories, systems that cooperate and systems that conflict. Whatever reality may be fundamentally, multiplicity appears everywhere.
For Spinoza, finite beings are modes of the one substance. They are real but dependent. A person, tree, river, or planet does not stand outside Nature as an independently grounded substance. Each is a determinate way in which Nature exists.
This offers one answer to the ancient problem of the one and the many: the many may be real without being metaphysically independent.
But the answer creates further questions.
What establishes the individuality of a mode?
How should we understand change within a reality governed by necessity?
Can genuine novelty arise, or does everything unfold from what the one substance necessarily is?
How much autonomy can finite beings possess if their existence and activity belong entirely within the causal order of Nature?
Analogies can help us imagine the problem without resolving it. A wave is distinguishable within an ocean without existing independently of the water and conditions producing it. A symphony possesses unity while depending upon differences of instrument, rhythm, harmony, movement, and silence. In neither case does unity require sameness.
But reality as a whole is not simply an ocean or a symphony. Those examples already presuppose a larger world within which oceans, waves, composers, instruments, and listeners exist.
Monism must therefore do more than provide an image of unity. It must explain how differentiation belongs to whatever it claims is fundamentally one.
This gives us a distinction that will remain important:
Dependence need not mean unreality.
But neither does calling something dependent explain everything about what it is.
Spinoza offers one model of differentiated unity. Monism after Spinoza offers others.
VI. Monism After Spinoza
Monism is not synonymous with Spinoza's substance metaphysics. Once the claim of unity is separated from his particular account of substance, very different monistic possibilities emerge.
Physicalism may be monistic. Everything may ultimately belong to physical reality without every phenomenon being conveniently described at the same level. Biology, psychology, and consciousness may remain meaningful while depending upon a physically continuous world.
Idealism may likewise be monistic. Reality may be fundamentally mental or experiential, with what we call physical reality understood within that more basic order.
The contrast is revealing. Physicalism and idealism can both affirm unity while disagreeing about what reality fundamentally is.
Thus:
Monism tells us that reality is fundamentally one more readily than it tells us what the one fundamentally is.
Nor is the meaning of fundamental self-evident. Something may be fundamental because everything else is composed from it, because everything else depends upon it, because it has explanatory priority, or because nothing deeper grounds it.
The disagreement therefore concerns more than the identity of the One. It concerns what metaphysical priority itself means.
This realization opens another possibility. Perhaps the dispute between physicalism and idealism assumes too quickly that reality must fundamentally belong to either category.
What if the mental and physical are both derivative properties of another fundamental monism?
VII. Neutral Monism and What Lies Beneath the Divide
Neutral monism questions whether the familiar distinction between mental and physical reaches all the way down to the foundations of reality.
Different versions of this possibility appear in thinkers such as William James and Bertrand Russell, although their philosophies should not be treated as identical. The shared intuition is more important for our purposes:
perhaps reality at its most basic is not adequately characterized as either mental or physical.
This does not mean that reality is composed of a mysterious third substance called “neutral stuff.” Such language can merely rename the problem. The more significant move is conceptual. Neutral monism asks whether mental and physical may describe different organizations, relations, or aspects of a reality whose fundamental character is not exhausted by either category.
This changes the debate inherited from our preceding essays.
Physicalism asks how experience becomes possible within physical reality. Idealism asks whether experience should instead receive metaphysical priority. Neutral monism asks whether both positions have accepted a distinction that may itself be derivative.
Its attraction is clear. If mental and physical characteristics belong to one more fundamental reality, there is no need to construct a bridge between independently existing worlds.
But neutrality is not explanation. Whatever lies beneath the distinction must still account for why reality can exhibit characteristics as different as physical structure and subjective experience. Saying that both arise from something more basic does not tell us how.
Neutral monism therefore sharpens rather than eliminates the question:
What kind of reality could become or appear as both?
There is still another way to formulate monistic unity.
Instead of asking what kind of reality is fundamental, we can ask whether fundamentality belongs to the whole rather than its parts.
VIII. Priority Monism - Is the Whole Fundamental?
Many things plainly exist in ordinary experience: organisms, mountains, planets, persons, molecules, institutions. But does the existence of many things establish that reality is fundamentally many?
Priority monism says no.
In contemporary metaphysics, Jonathan Schaffer has argued for a distinction between how many things exist and how many things are fundamental. Priority monism need not deny the existence of parts. It proposes instead that the concrete cosmos as a whole possesses metaphysical priority over them.
This differs importantly from the stronger claim that only one concrete thing exists. The issue is not primarily existence but dependence.
A wave provides a useful, if limited, illustration. A wave possesses location, duration, structure, and effects. It is real. Yet its existence depends upon the larger body of water and the conditions through which it forms. Dependence does not make the wave illusory.
Priority monism asks whether something analogous might hold at the largest metaphysical scale. Perhaps the universe is not fundamentally constructed from independently existing pieces whose aggregation eventually produces a whole. Perhaps the character and possibility of the parts depend in some sense upon the whole to which they belong.
This proposal should not be confused with a scientific conclusion. Features of contemporary physics, including discussions of holism and entanglement, have entered arguments about metaphysical dependence, but physics does not simply prove priority monism. The philosophical claim requires arguments concerning what counts as fundamental and how dependence should be understood.
Its importance for our inquiry is nevertheless considerable. Priority monism shows that we need not choose between saying that only the One exists or by saying that reality is fundamentally a collection of independent many.
Many things may be real.
The question is whether any of them are metaphysically independent of the whole.
IX. The Price of Unity
Every metaphysical proposal solves some problems by accepting responsibility for others. Monism gains explanatory integration, but it must explain the differentiation contained within that integration.
Its first debt is individuality. If finite beings are modes, manifestations, dependent parts, or organizations of one reality, what makes them genuinely distinct? Dependence cannot simply become another word for insignificance.
Its second debt is difference. Mental and physical characteristics, living and nonliving systems, subjects and objects may all belong within one reality. But unity alone does not explain why these differences exist or why they matter.
Its third debt is novelty and contingency. This problem is particularly sharp in Spinoza's necessitarian system. If everything follows necessarily from the nature of the one substance, what becomes of alternative possibilities? Other monisms need not share Spinoza's determinism, so the problem should not be attributed to monism as such. But every monism must say something about whether the one reality can produce genuinely new configurations, histories, or forms.
Its fourth debt is agency. If individuals are deeply dependent upon the whole, what kind of causal efficacy or freedom can properly belong to them? Again, dependence does not automatically eliminate agency, but neither does monism guarantee it.
Finally comes explanatory adequacy. Calling everything a mode, aspect, manifestation, organization, or part of one reality cannot itself constitute an explanation. A monism capable of accommodating every possible difference simply by declaring it another expression of the One risks becoming difficult to test even philosophically.
The price of unity is therefore not necessarily the loss of the many.
It is the obligation to explain them.
X. Unity Without Erasure
The strongest insight of monism may not be that everything is secretly the same.
It may be that difference does not necessarily require separation.
That distinction allows us to understand unity more carefully. One reality need not mean one undifferentiated object. Dependence need not mean unreality. Plurality need not mean metaphysical independence. Different levels of description need not identify different worlds.
But these distinctions also prevent monism from taking the easy route. If differences are genuine, they must be explained rather than dissolved.
A symphony again provides a limited image. Its unity does not result from every instrument producing the same sound. Its identity depends upon differentiated contributions, relations, sequences, tensions, harmonies, and silences. Remove the differences and the unity itself changes.
Reality may be nothing like a symphony in its fundamental ontology. The analogy nevertheless exposes the conceptual possibility of differentiated unity - a whole whose unity does not require the erasure of internal difference.
Whether metaphysical monism can actually provide such an account remains open.
Spinoza locates plurality within modes of one substance.
Physicalist and idealist monisms identify different candidates for the fundamental order.
Neutral monism questions whether the physical/mental distinction is fundamental at all.
Priority monism relocates unity in the dependence of parts upon a whole.
None of these approaches establishes simply that reality is one.
Instead, they change the question they bring to multiplicity.
Perhaps we need not always ask which side of a metaphysical contrast is finally real. We can also ask:
What kind of reality could contain the contrast itself?
Monism places that possibility before us without yet deciding whether it succeeds.
Conclusion: Can Reality Be One and Genuinely Many?
We began with a proposition that sounded almost elementary: reality is one.
The proposition became more difficult as soon as we asked what one means.
One substance is not the same claim as one kind of reality. One kind is not the same as one metaphysically fundamental whole. Physicalism, idealism, Spinozism, neutral monism, and priority monism can all affirm forms of unity while offering markedly different accounts of what that unity entails.
Spinoza gives us the most sustained historical example considered here. His one infinite substance - God or Nature - removes the ontological separation between creator and creation and relocates thought and extension within one reality. Finite things remain real as modes, though not as independently grounded substances. The resulting system displays both the power and the difficulty of monism: extraordinary integration accompanied by demanding questions concerning necessity, individuality, freedom, and multiplicity.
Later forms of monism loosen Spinoza's particular commitments without escaping the central problem. If reality is fundamentally physical, experience must somehow belong within that unity. If reality is fundamentally mental or experiential, physical order must be accounted for. If the foundation is neutral, the emergence or manifestation of both requires explanation. If the whole is prior to its parts, the reality and efficacy of those parts must still be preserved.
The deepest question raised by monism may therefore not be whether the world contains many things. Clearly it does at the levels at which we ordinarily encounter it. The deeper question is whether multiplicity requires multiple independent foundations of reality.
Monism answers: perhaps not.
That answer deserves serious consideration because it loosens an assumption that has followed metaphysics repeatedly - that sufficiently profound difference must eventually become ontological separation.
Yet monism carries an equal warning in the other direction. Unity cannot become an explanation purchased by erasing whatever does not fit comfortably within it. A metaphysics of the One must eventually return to the world of the many: different beings, properties, processes, experiences, histories, and possibilities. If these differences are real, the unity must be capable of containing them without making their reality merely verbal.
We therefore arrive not at a verdict but at a better question:
Can reality be fundamentally one while its plurality remains genuinely real?
Spinoza answered in one way. Neutral and priority monists answer differently. Other philosophies will resist the premise altogether.
And that is where our inquiry should remain open.
For perhaps the next question is not whether reality is one or many, but what gives its apparent unity and diversity their form, persistence, and intelligibility.
Perhaps what is fundamental is neither simply the One nor the many.
What if reality is fundamentally structural?
James, William. Essays in Radical Empiricism. New York: Longmans, Green, and Co., 1912.
Russell, Bertrand. The Analysis of Mind. London: George Allen & Unwin, 1921.
Schaffer, Jonathan. “Monism.” In The Stanford Encyclopedia of Philosophy, edited by Edward N. Zalta and Uri Nodelman. Stanford University, Metaphysics Research Lab. Stanford Encyclopedia of Philosophy - “Monism”
Schaffer, Jonathan. “Monism: The Priority of the Whole.” The Philosophical Review 119, no. 1 (2010): 31-76. “Monism: The Priority of the Whole”
Spinoza, Baruch. Ethics. Edited and translated by Edwin Curley. Introduction by Stuart Hampshire. London: Penguin Books, 1996.
Michael Della Rocca provides a contemporary interpreter capable of helping us understand the rigor and interconnectedness of Spinoza's system. His inclusion is important because Spinoza can easily be simplified into slogans - “everything is one,” “God is nature,” or “individuals are merely appearances.” Della Rocca helps recover the philosophical arguments concerning substance, dependence, intelligibility, mind and body, necessity, and freedom that make Spinoza's monism considerably more demanding than such summaries suggest.
William James moves the discussion beyond classical substance metaphysics. His radical empiricism questions sharp divisions between knower and known, subject and object, and consciousness and its contents. His language of “pure experience” provides one important historical route toward the possibility that the mental and physical may not represent the most fundamental division within reality. His inclusion also reminds us that challenging dualism does not require returning automatically to either materialism or idealism.
Bertrand Russell carries this problem into twentieth-century analytic philosophy. His investigations of sensation, mind, matter, and physical and psychological causation show how the search for a more neutral account of reality continued after James. Russell is particularly useful because his developing position cautions us against treating neutral monism as a single, settled doctrine. The category names a family of attempts to reconsider whether the distinction between mental and physical reaches all the way to metaphysical foundations.
Jonathan Schaffer brings the question of monism directly into contemporary metaphysics. Priority monism changes the question from “How many things exist?” to “How many things are fundamental?” On this account, the existence of persons, organisms, planets, and other parts need not be denied in order to argue that the cosmos as a whole possesses metaphysical priority. Schaffer therefore gives us a particularly clear contemporary example of how unity can be proposed without simply declaring the many unreal.
The Stanford Encyclopedia of Philosophy entry on monism is included for a different reason. It provides the reader with a conceptual map rather than another metaphysical system. Its distinctions among kinds of monism help clarify one of the central lessons of this essay: saying that reality is “one” remains ambiguous until we specify what is being counted and in what sense it is one.
Together these readings deliberately move across several different meanings of metaphysical unity:
Spinoza asks whether there is one substance.
James and Russell ask whether the mental and physical distinction reaches the foundations of reality.
Schaffer asks whether one whole may be fundamental even while many parts genuinely exist.
These thinkers have not been chosen because they converge upon a single doctrine of monism. They have been chosen precisely because they do not. Their disagreements expose how much remains undecided after we make the apparently simple statement: Reality is one.
| Form of Monism | What Is “One”? | Central Claim | Representative Example |
|---|---|---|---|
| Substance Monism | Substance | Ultimately there is one fundamental substance upon which finite things depend. | Spinoza |
| Kind Monism | Fundamental kind of reality | Everything ultimately belongs to one basic kind or category of reality. | Physicalist or idealist monisms |
| Existence Monism | Concrete reality | Ultimately only one concrete entity exists. | Strong forms of contemporary monism |
| Neutral Monism | Fundamental basis or order | Mental and physical may not be fundamental or exhaustive categories of reality but may arise from, describe, or belong to something more basic. | James, Russell |
| Priority Monism | Fundamental whole | Many things genuinely exist, but the whole is metaphysically prior to or more fundamental than its proper parts. | Schaffer |
These forms of monism should not be treated as interchangeable. A philosopher may affirm unity in one sense while rejecting it in another. Someone might accept that everything belongs to one fundamental kind of reality without claiming that only one concrete thing exists. Another might accept the reality of innumerable individual things while maintaining that none is metaphysically independent of the whole.
The crucial question is therefore not merely:
Is reality one?
It is also:
One what - and in what sense?
Once that distinction is made, a further question follows.
- Whatever kind of unity is proposed, what metaphysical status remains for the many?
- Are individual things independent realities, dependent realities, modes, parts, organizations, manifestations, or something else?
Monism does not supply one answer to these questions. It names a family of attempts to understand how the apparent multiplicity of reality might belong within a more fundamental unity.
And that is precisely why the deceptively simple proposition with which this essay began remains a metaphysical question rather than a conclusion:
Reality is one.
Or, restated as a question, "Is reality one?"