Orientation
What Metaphysics Is
Metaphysics is the study of the most general features of reality: what exists, what it is to exist, what kinds of things there fundamentally are, and how they hang together.
Where the special sciences each carve off a region of reality — physics studies matter in motion, biology living systems — metaphysics asks after being as such: not this or that being, but being qua being (Aristotle's tò òn hê òn). It is the discipline that refuses to take for granted the categories every other inquiry quietly assumes.
A note on the name
The word is a historical accident. Aristotle called this inquiry first philosophy (prōtē philosophia), the science of being qua being, and sometimes theology. The label "metaphysics" comes from the editor Andronicus of Rhodes (1st c. BCE), who arranged Aristotle's untitled treatises on these topics after the Physics — tà metà tà physiká, "the [books] after the Physics." A librarian's ordering note hardened into the name of a discipline, and the prefix meta- ("after") was later reread as "beyond," giving the popular but etymologically spurious sense of metaphysics as the study of what lies beyond the physical.
The classical division
Systematized by Christian Wolff in the 18th century, the traditional map splits the field in two:
- General metaphysics — ontology: being in general, existence, substance, properties, identity, cause, modality.
- Special metaphysics — three regional inquiries into the highest kinds of being: rational cosmology (the world as a whole), rational psychology (the soul or mind), and natural theology (God, the ground of being).
Modern analytic metaphysics has largely dropped the tidy Wolffian scheme, but it still circles the same questions. The guide below is organized by question rather than by school — fifteen deep problems, each with the concepts that structure it and the positions that divide it. Use the explorer immediately below to filter and search across every position in the guide, or read straight through.
Question I
Being & Existence
What does it mean to say something exists? Is "exists" a genuine property of things? What is the most general inventory of what there is?
Key concepts
- Being vs. beings — the general fact of existence versus the particular things that exist. Heidegger names the gap the ontological difference and charges the whole tradition with forgetting the question of Being itself (Seinsfrage).
- Categories of being — Aristotle's ten highest genera under which anything whatever falls: substance, quantity, quality, relation, place, time, position, state, action, passion. Everything else is said "of" or "in" a substance.
- Is existence a predicate? — Kant's famous denial: existence adds nothing to the concept of a thing (a hundred real dollars contain no more coins than a hundred imagined ones). Frege and Russell formalize this — existence is not a first-order property of objects but a second-order property, expressed by the existential quantifier ("there is an x such that…").
- Ontological commitment — Quine's criterion, from "On What There Is" (1948): to be is to be the value of a bound variable. You are committed to whatever your best theory must quantify over. His slogan — "no entity without identity" — admits no thing you cannot say when it is the same as, or different from, another.
Positions & thinkers
Parmenides makes the founding statement of ontology: being is one, ungenerated, indivisible, changeless — "what is, is, and cannot not-be." Non-being cannot be thought or spoken, and so change is illusion, the standing challenge every later ontology must answer. Heraclitus is the counter-pole: reality is flux, "you cannot step into the same river twice," unity held together in tension. Aristotle refuses both extremes — being is not a single genus but is "said in many ways" (pollachōs legetai); the categories map those ways, with substance primary.
At the outer edge sits Meinong, whose jungle of objects grants that even non-existent and impossible objects — the golden mountain, the round square — subsist and can bear properties. Against him, Quine preaches a "desert-landscape" ontology tied to natural science: admit only what our best theory quantifies over. Heidegger reopens the question of the meaning of Being through Dasein, the entity (us) for whom Being is a question.
The Islamic contribution — essence and existence
Ibn Sīnā (Avicenna) draws the single most consequential distinction in this area: in any contingent thing, its essence (māhiyya, "whatness") is separable in thought from its existence (wujūd). Existence is "superadded" to essence — the essence of a horse does not by itself guarantee that any horse exists. Only in one being is essence identical with existence: the Necessary Being (wājib al-wujūd), whose essence just is to exist. Everything else is mumkin al-wujūd, merely possible-in-itself and existent only through another. This distinction drives his cosmological argument and, transmitted through translation, shapes Aquinas.
Mullā Ṣadrā (d. c. 1640) inverts a long essentialist tradition with aṣālat al-wujūd — the primacy of existence. Existence, not essence, is the fundamental reality; essences are mind-derived abstractions from a single graded field of being. Being admits of tashkīk (systematic gradation or modulation): one reality, present in more and less intense degrees — a metaphysics of existence itself rather than of things.
Question II
Substance — the bearers of reality
What are the basic, independent things that have properties and undergo change? Is there an underlying "thing" beneath the properties, or only properties all the way down?
Key concepts
- Substance — traditionally, what exists in its own right and bears properties (a horse, a person), as opposed to properties, which exist only in a substance.
- Hylomorphism — Aristotle's analysis of a substance into matter (hylē) and form (morphē); the form makes it the kind of thing it is. A bronze statue is bronze (matter) shaped into a figure (form); strip the form and you have only a lump.
- Substratum vs. bundle — is there a propertyless bearer "underneath" (a bare particular), or is a thing just a bundle of its properties?
- Trope — a particular property (this red, not redness in general).
Positions & thinkers
Aristotle holds that primary substances are concrete individuals; universals and properties are ontologically derivative. Descartes defines a substance as what needs nothing but itself (and God) to exist, and finds two created kinds: res cogitans (thinking, unextended) and res extensa (extended, unthinking). Spinoza pushes the definition to its limit: since a substance must be causally and conceptually self-sufficient, only the whole of reality qualifies — radical monism, one substance, Deus sive Natura (God-or-Nature), of which everything else is a mode. Leibniz goes the opposite way: reality is composed of infinitely many simple substances, monads — partless, "windowless," each mirroring the whole universe from its own point of view, coordinated by pre-established harmony.
On the underlying structure of a single thing, three camps divide. Substratum theory (Locke's "something, I know not what"; Bergmann's bare particulars) posits a thin bearer that individuates and supports properties. Bundle theory (Hume, Russell) denies any bare bearer: an object just is a co-located bundle of properties. Trope theory (D. C. Williams, Keith Campbell) makes the world's basic constituents property-particulars, and builds both substances and universals out of them.
Question III
Universals — one over many
Two apples are both red. Is there one thing, redness, that both share — or only two red particulars and a resemblance?
This is the problem of universals, the longest-running dispute in metaphysics, alive from Plato through the medieval schools to contemporary philosophy of science.
Key concepts
- Universal — a repeatable feature that can be wholly present in many places at once (redness, humanity, being-triangular).
- Particular — a non-repeatable individual (this apple).
- Ante rem vs. in re — universals existing prior to and apart from their instances (Platonic Forms) versus in their instances (Aristotelian immanent universals).
Positions & thinkers
Platonic realism places the Forms transcendently, outside space and time; particulars are what they are by participating in them. This grounds the intelligibility of the world but strains under the Third Man regress (if redness needs a further form to explain what it shares with red things, the explanation never stops). Aristotelian (immanent) realism keeps universals real but locates them only in their instances, not in a separate realm.
Nominalism holds that only particulars exist; "universals" are just names, predicates, classes, or resemblances. William of Ockham is the great medieval nominalist — and Ockham's razor (do not multiply entities beyond necessity) is his weapon. Conceptualism occupies the middle: universals exist, but as concepts in the mind, not mind-independent things. Abelard holds this ground in the debate that Boethius had transmitted from Porphyry's three questions — do genera and species exist in reality or only in thought? if real, are they bodily or incorporeal? separate from sensibles or in them? Into the modern era, D. M. Armstrong defends a scientific realism about universals: admit just those universals that mature physics needs, discovered a posteriori, immanent in things.
Question IV
Persistence & Change
How can one and the same thing persist through time while its properties change? And what makes x at one time identical to y at another?
Key concepts
- Numerical vs. qualitative identity — being one and the same thing versus being exactly alike. Two new coins are qualitatively identical but numerically two.
- Leibniz's Law — the indiscernibility of identicals (if a = b, they share all properties) and the more contested identity of indiscernibles (if they share all properties, a = b).
- Temporary intrinsics — the puzzle of how a thing can be bent at one time and straight at another without contradiction.
Positions & thinkers
Endurantism says a persisting thing is wholly present at each moment it exists; it has no temporal parts — the whole of you is here now, and the whole of you was here yesterday. Perdurantism says a thing perdures by having distinct temporal parts at different times; the whole object is a four-dimensional "spacetime worm" of which any given moment is only a slice (Lewis, Quine). Exdurantism, or stage theory, makes the object a momentary stage, analyzing all talk of persistence through relations among stages (Sider, Hawley).
Classic puzzles
The Ship of Theseus: replace every plank one by one, then reassemble the discarded originals into a second ship — which is the original? And the statue and the clay: one lump of clay, one statue, seemingly two things occupying one place at once — the problem of material constitution and coincidence. Both press on whether identity through change is a fact about the world or an artifact of how we count.
Question V
Personal Identity
A special, high-stakes case: what makes you the same person from childhood to old age? What matters for survival?
Positions & thinkers
The soul or substance view holds that you are an immaterial substance persisting through all change (Descartes; most religious traditions). Locke relocates identity in continuity of consciousness and memory, not sameness of soul or body — later refined into overlapping chains of psychological connection. Eric Olson's animalism answers differently again: you are a human animal, and your identity is the persistence of the organism, not of a psychology.
Derek Parfit (Reasons and Persons, 1984), through fission and teletransportation thought experiments, argues that personal identity is not a deep further fact and not what rationally matters in survival — what matters is Relation R, psychological connectedness and continuity, which can hold to varying degrees and even branch. This converges strikingly with the Buddhist doctrine of anattā (no-self): the "person" is a bundle of ever-changing aggregates (skandhas), with no persisting substantial self beneath them. Against naïve memory theories, Reid's brave officer paradox shows they violate the transitivity of identity — the old general remembers the young officer, the young officer remembers the flogged boy, yet the general remembers nothing of the boy.
Question VI
The Nature of Time
Does time really pass? Are past and future as real as the present? Is temporal becoming an objective feature of the world or of our perspective?
Key concepts
- A-series vs. B-series — McTaggart's distinction (from "The Unreality of Time," Mind, 1908). The A-series orders events as past / present / future — a tensed, moving structure. The B-series orders them as earlier-than / later-than — a fixed, tenseless structure. His argument for the unreality of time: real change requires the A-series, but the A-series is contradictory (every event is past and present and future), so time is unreal.
- A-theory vs. B-theory — is tense and passage objective (A), or is reality fundamentally tenseless, with "now" as indexical as "here" (B)?
Positions & thinkers
Presentism holds that only the present exists; past and future are unreal. Eternalism, or the block universe, holds that all times are equally real — the universe is a four-dimensional block, "now" merely marking one's location within it (the natural partner of relativity). The growing block splits the difference: past and present are real and fixed, the future open and unreal, so reality accretes moment by moment.
Augustine (Confessions XI) frames the enduring puzzle — "What then is time? If no one asks me, I know; if I wish to explain, I know not" — and locates time in the mind's distentio, its stretching between memory and expectation. McTaggart, A. N. Prior (founder of tense logic, defending real tense), and D. C. Williams ("The Myth of Passage," attacking it) anchor the modern debate. Related live problems: the arrow of time (why does time have a direction?) and time travel (the grandfather paradox).
Companion question — space
Is space a real container — Newton's absolute space, substantivalism — or merely the system of relations among bodies, Leibniz's relationism? The Leibniz–Clarke correspondence and Newton's rotating-bucket argument are the classic battleground, revived in the philosophy of general relativity through the hole argument.
Question VII
Causation
What is it for one thing to cause another? Is there a real "productive" connection in nature, or only patterns we project?
Key concepts
- Aristotle's four causes — the material (what it's made of), formal (its form or essence), efficient (what brings it about), and final (that for the sake of which). Modern usage narrows "cause" almost entirely to the efficient.
- Necessary connection — is there a "glue" binding cause to effect, or only regular succession?
Positions & thinkers
Hume's regularity theory is the field's most influential move: we never observe a necessary connection, only constant conjunction plus the mind's habit of expectation; causation "in the objects" is nothing over and above regular succession. Kant answers that causal necessity is not read off the world but imposed by the understanding as a condition of possible experience. David Lewis offers a counterfactual analysis: c causes e roughly iff, had c not occurred, e would not have occurred (spelled out through possible worlds). Neo-Aristotelian powers theorists (Molnar, Mumford, Bird) restore genuine necessity to nature: things have real causal powers, and causation is their manifestation. And interventionists (Woodward, Pearl) treat causes as what you could manipulate to change effects — causation as difference-making under intervention.
Islamic occasionalism
Al-Ghazālī, in the seventeenth discussion of the Tahāfut al-Falāsifa, denies any necessary connection between what we call cause and effect: when cotton meets fire, it is not the fire but God who creates the burning; the two are merely habitually conjoined. This occasionalism — developed in Ash'arite kalām, and independently by Malebranche — anticipates Hume's critique of necessary connection by six centuries, while drawing the opposite theological conclusion: the constant conjunction is God's customary act (sunnat Allāh), not blind regularity.
A scholarly caveat
How thoroughgoing al-Ghazālī's occasionalism really was is contested. On the traditional reading (defended by Michael Marmura) he restricts genuine causal power to God alone. Recent scholarship — Richard Frank, and especially Frank Griffel — argues that his primary aim was narrower: to secure the possibility of miracles against the philosophers' claim that nature runs by necessity, leaving room for real secondary causes in creatures. The label "occasionalist" fits the seventeenth discussion's opening argument better than it fits the whole of his thought.
Related contemporary problem — mental causation
If the physical world is causally closed, how can mental states cause anything without overdetermining their effects? Jaegwon Kim's exclusion argument presses this hard against non-reductive physicalism.
Question VIII
Modality — necessity, possibility, essence
Some truths are merely contingent (Paris is the capital of France), others necessary (2 + 2 = 4). What grounds this difference? And are there real essences?
Key concepts
- De dicto vs. de re — necessity attaching to a proposition ("necessarily, bachelors are unmarried") versus to a thing itself ("this water is necessarily H₂O").
- Possible worlds — total ways things could have been; a proposition is necessary if true in all of them, possible if true in at least one.
- Rigid designator — a term that picks out the same object in every possible world (proper names, natural-kind terms).
- Essence — what a thing must be to be the thing it is; its identity conditions.
Positions & thinkers
Leibniz first brings possible worlds into philosophy as ideas in God's intellect: infinitely many are conceived, and the actual world is the best of them. David Lewis takes them literally — modal realism holds that possible worlds are concrete, spatiotemporally isolated universes, as real as our own, with "actual" merely indexical (our world, from our vantage). Ontologically extravagant, theoretically powerful. Actualists (Plantinga, Stalnaker) keep the machinery but deflate the ontology: possible worlds are abstract objects — maximal states of affairs or propositions — and only the actual world is concrete.
Kripke (Naming and Necessity, delivered as lectures in 1970) is the modern watershed. Names are rigid designators; there are necessary a posteriori truths (Hesperus = Phosphorus; water = H₂O — discovered empirically, yet true in all worlds) and contingent a priori truths (the length of the standard meter). The upshot restored essentialism to respectability. Kit Fine then argues that essence is not reducible to modal necessity: many things are necessarily such-and-such — Socrates is necessarily a member of the set {Socrates} — without that being part of what Socrates essentially is. Essence is the more basic, "real-definitional" notion.
Cross-reference
Ibn Sīnā's distinction between necessary and contingent being (Question I) is a foundational contribution here, powering the modal version of the cosmological argument (Question XIV).
Question IX
Free Will & Determinism
If every event is fixed by prior events and the laws of nature, can any of our choices be free? And would mere randomness help?
Key concepts
- Determinism — a complete state of the world plus the laws entails a unique future.
- Could have done otherwise — the principle of alternate possibilities: freedom (and responsibility) requires genuinely open alternatives.
- Sourcehood — an alternative gloss: freedom is being the true source or origin of one's action, whether or not alternatives were open.
Positions & thinkers
Hard determinists and hard incompatibilists hold that the causal order rules out free will, so we lack it (Spinoza, d'Holbach; and among contemporaries Derk Pereboom and Galen Strawson, whose "basic argument" targets ultimate responsibility). Libertarians hold that we have free will and determinism is therefore false, in two forms: agent-causal — a self, not merely prior events, causes the action (Reid, Chisholm, O'Connor) — and event-causal — indeterministic yet controlled (Robert Kane). Compatibilists deny the conflict: freedom means acting from one's own will without external constraint, not metaphysical openness (Hobbes, Hume; Harry Frankfurt, who casts freedom as higher-order endorsement of one's desires and whose cases attack the alternate-possibilities principle; and Dennett). The sharpest case for incompatibilism is Peter van Inwagen's consequence argument: if our acts are consequences of the remote past and the laws, and neither is up to us, then our acts are not up to us.
The Islamic dimension
The Muʿtazila defended human free creation of acts, since divine justice requires it; the Ashʿariyya replied with kasb ("acquisition") — God creates the act, the human "acquires" it and so is accountable — a subtle, compatibilist-leaning mediation between omnipotence (qadar) and responsibility.
Question X
Mind & Body
Consciousness and thought seem utterly unlike anything physical. What is the mind, and how does it fit into a physical world?
This overlaps philosophy of mind, but it is metaphysically central: it is a question about the fundamental kinds of thing there are.
Key concepts
- The hard problem (Chalmers) — even a complete account of brain function leaves unexplained why there is something it is like to undergo it.
- Qualia — the felt, subjective qualities of experience (the redness of red, the ache of pain).
- Supervenience — the mental depends on and is fixed by the physical: no mental difference without a physical difference.
Positions & thinkers
Substance dualism (Descartes) makes mind and body distinct substances; the notorious interaction problem — how can the unextended move the extended? — has dogged it ever since. Property dualism and panpsychism keep one kind of substance but treat mental properties as fundamental and irreducible; panpsychism (revived by Chalmers and Goff) makes experience a basic, ubiquitous feature of matter. Physicalism holds that the mind is physical, in several variants: the identity theory — mental states are brain states (Place, Smart); functionalism — mental states are defined by causal role and so are multiply realizable, capable of being implemented in neurons or silicon alike (Putnam); eliminativism — folk mental categories are a false theory to be replaced (the Churchlands); and non-reductive physicalism — the mental supervenes on but does not reduce to the physical. Idealism runs the reduction the other way: the physical reduces to the mental. Berkeley: esse est percipi, to be is to be perceived, with no mind-independent matter; German idealism (Fichte, Hegel) develops reality as the self-unfolding of spirit or reason.
Landmark challenges to physicalism
Nagel's "What Is It Like to Be a Bat?" (the subjective character of experience eludes objective description); Jackson's knowledge argument (Mary the color scientist, who knows every physical fact about color yet learns something new on first seeing red); and Levine's explanatory gap.
Question XI
The Fundamental Structure of Reality
How many ultimate things are there — one or many? And of what kind is reality ultimately made?
Key concepts & positions
Monism vs. pluralism asks whether reality is ultimately one (Parmenides; Spinoza's single substance; Bradley's Absolute) or many. A crucial modern refinement distinguishes existence monism (only one thing exists) from priority monism (Jonathan Schaffer): many things exist, but the cosmos as a whole is metaphysically prior to its parts, which are its abstractions. On the question of kind: materialism / physicalism makes the fundamental stuff physical; idealism makes it mental; neutral monism (Russell, James) makes it neither, with mind and matter both derived from it; dualism posits two irreducible fundamental kinds.
The contemporary frontier — grounding and fundamentality
Much current analytic metaphysics has shifted from "what exists" to "what is fundamental, and what depends on it." Metaphysical grounding is a non-causal "in virtue of" relation — the party exists in virtue of the people; the mental holds in virtue of the physical. Fine, Rosen, Schaffer, and Sider (on the world's fundamental structure) recast the old realism debates as questions about layers of dependence rather than mere lists of entities.
Question XII
Realism vs. Anti-Realism
Does the world exist and have its character independently of any mind, or is reality in some way constituted by thought, language, or perception?
Positions & thinkers
Metaphysical realism holds that the world and its structure are mind-independent, and truth is correspondence to that world. Kant's transcendental idealism stages a Copernican revolution: we know only appearances (phenomena), structured by the mind's own forms — space, time, and the categories — while things-in-themselves (noumena) are real but unknowable; objects conform to our cognition rather than cognition to objects. Hegel's absolute idealism pushes further: the real is the rational, unfolding dialectically, and the distinction between mind and world is overcome in the Absolute. Modern anti-realisms come in several keys — Dummett (anti-realism motivated by a verificationist theory of meaning), Putnam's internal realism ("objects" exist only relative to a conceptual scheme), and Goodman's irrealist "ways of worldmaking."
Comparative note
Advaita Vedānta (Śaṅkara) offers a non-Western idealist monism: Brahman alone is ultimately real, the plural world is māyā (appearance), and liberation is recognizing the identity of ātman and Brahman — a striking parallel to, and contrast with, both Parmenidean monism and Mullā Ṣadrā's waḥdat al-wujūd (unity of being).
Question XIII
Parts & Wholes — composition
When do some things add up to a further thing? Do "tables" and "crowds" really exist over and above the particles arranged tablewise or the people arranged crowdwise?
Mereology is the formal theory of the part–whole relation; the Special Composition Question (van Inwagen) asks: under what conditions do some objects compose a further object?
Positions & thinkers
Mereological nihilism holds that nothing composite exists — there are only mereological simples (fundamental particles), and "tables" are just simples arranged tablewise. Universalism, or unrestricted composition (David Lewis, Sider), goes to the opposite extreme: any things whatever compose a further object, however scattered — your nose plus the Eiffel Tower plus a distant star form a legitimate, if gerrymandered, object. Restricted composition (van Inwagen) charts a middle course: composition occurs only in special cases — for him, only when the activity of the parts constitutes a life, so the only composite objects are living organisms.
Related notions
Gunk — matter infinitely divisible, with no simples at the bottom — versus atomism, on which composition bottoms out in partless simples.
Question XIV
God & the Ground of Being
Is there a necessary, self-existent ground of all contingent reality? This is metaphysics' oldest overlap with theology, pursued by argument rather than revelation.
Key arguments & concepts
Cosmological arguments reason from the existence or contingency of the world to a first or necessary cause: Aquinas's Five Ways (motion, causation, contingency, degrees, teleology); the kalām cosmological argument (al-Kindī, al-Ghazālī, revived by William Lane Craig) — the universe began to exist, whatever begins has a cause, therefore the universe has a cause; and Leibniz's version from the Principle of Sufficient Reason (why is there something rather than nothing?). Ibn Sīnā's contingency argument — from mumkin al-wujūd to wājib al-wujūd — is the modal spine of the whole family.
Ontological arguments run entirely a priori, from the concept of God to God's existence. Anselm: God is that than which nothing greater can be conceived, and such a being must exist in reality, not merely in the understanding. Descartes' version makes existence belong to the essence of a perfect being; Gödel gives a formalization; Plantinga's modal version argues that a maximally great being exists in some possible world, hence — given the modal system S5 — in all, hence in this one.
The divine attributes are themselves metaphysical notions: aseity (self-existence), necessity, simplicity (no composition of parts), and timelessness.
Positions
Classical theism (God as necessary, simple, timeless, immutable — Aquinas, Ibn Sīnā, Maimonides) stands against process theism (Whitehead, Hartshorne — God as dipolar, in genuine temporal relation to a becoming world), with Tillich's "God as the ground of being," beyond the subject/object of ordinary existence-talk, as a third path.
Question XV
Is Metaphysics Even Possible?
Can reason reach truths about reality beyond all possible experience? Or is metaphysics a tissue of pseudo-problems?
The critical tradition and its answers
Kant argues that transcendent metaphysics — soul, cosmos, God — inevitably overreaches the bounds of possible experience and collapses into antinomies, equally good proofs of contradictory theses. Legitimate metaphysics is only the critique of the mind's own a priori structure. Logical positivism — the Vienna Circle, Carnap, Ayer — goes further: metaphysical statements are neither analytic nor empirically verifiable, hence cognitively meaningless, not false but nonsense (Carnap, "The Elimination of Metaphysics Through Logical Analysis of Language"). Carnap's internal vs. external distinction dissolves many disputes: "do numbers exist?" is trivial inside the framework of arithmetic and merely a pragmatic choice-of-language outside it.
Quine dismantles the analytic/synthetic distinction ("Two Dogmas of Empiricism") and with it the positivists' basis for excluding metaphysics; he rehabilitates ontology as continuous with natural science — we should believe in whatever our best total theory of the world must quantify over. This is naturalized metaphysics. The neo-Aristotelian revival (Fine, Lowe, Schaffer, and others) then argues that the interesting questions were never mainly about existence — which is often cheap — but about essence, grounding, fundamentality, and powers, reviving a robust, non-positivist metaphysics of structure.
How metaphysics is done
Its characteristic tools: conceptual analysis; thought experiments and intuitions (the Ship of Theseus, the teletransporter, philosophical zombies); theoretical virtues borrowed from science (parsimony — Ockham's razor — explanatory power, elegance, fit with total theory); and, in the naturalist camp, close attention to what our best physics actually posits.
Summary
A Map to Keep
The whole field on one page — fifteen questions, the core dispute animating each, and the representative positions that divide it.
| Big question | Core dispute | Representative positions |
|---|
| What is being? | Is existence a property? What's the inventory? | Aristotle's categories · Quine's ontological commitment · Ibn Sīnā's essence/existence · Ṣadrā's primacy of existence |
| What is substance? | Bearer beneath properties, or bundle? | Hylomorphism · substratum · bundle · trope |
| Universals | One-over-many | Platonic & Aristotelian realism · nominalism · conceptualism |
| Persistence | How survive change? | Endurantism · perdurantism · stage theory |
| Personal identity | What makes you you? | Soul · psychological continuity · animalism · Parfit |
| Time | Does time pass? | A- vs. B-theory · presentism · eternalism · growing block |
| Causation | Real connection or regularity? | Hume · counterfactual · powers · occasionalism |
| Modality | What grounds necessity? | Lewis's worlds · actualism · Kripkean essentialism |
| Free will | Compatible with determinism? | Hard determinism · libertarianism · compatibilism |
| Mind & body | Where does consciousness fit? | Dualism · physicalism · idealism · panpsychism |
| Fundamental structure | One or many; of what kind? | Monism · pluralism · materialism · idealism · grounding |
| Realism | Mind-independent world? | Realism · Kantian idealism · anti-realism |
| Parts & wholes | When do things compose? | Nihilism · universalism · restricted composition |
| God / ground of being | A necessary first reality? | Cosmological · ontological arguments · classical vs. process theism |
| Is metaphysics possible? | Legitimate knowledge? | Kant · positivism · Quinean naturalism · neo-Aristotelian revival |
Closing
The Threads That Interlock
Two cross-cutting observations are worth carrying into any deeper study.
First, the questions interlock. Your theory of time constrains your theory of persistence, which in turn constrains personal identity. Your view on universals shapes your view on modality and laws of nature. Choose a position in one corner of the field and you have quietly committed yourself in several others.
Metaphysics is less a settled body of doctrine than a small set of very deep questions that every serious civilization has been unable to leave alone.
Second, the same problems recur across traditions with independent vocabularies. The essence/existence distinction runs from Ibn Sīnā to Aquinas to the existentialists. Occasionalism links Ash'arite kalām to Malebranche to Hume. No-self connects Parfit to the Buddhist skandhas. Monism ties Parmenides to Spinoza to Śaṅkara to Ṣadrā. The reader who learns to see these convergences has learned something about the structure of the problems themselves — and about the minds, in every age, that could not stop asking.