Metaphysics and Ontology
Metaphysics is the philosophical study of the fundamental nature of reality.
It asks what there is, what kinds of things there are, and what relations they bear to one another.
Ontology, often treated as a branch of metaphysics, is more narrowly the study of being qua being.
It catalogs the systematic categories of existence.
Aristotle gave the name “first philosophy” to the inquiry into being and its principles.
The term “metaphysics” derives from the editorial placement of his treatise after (meta) the Physics in the Andronicus of Rhodes ordering, around 60 BCE.
Greek origins
Pre-Socratics
The Pre-Socratic philosophers worked in the 6th and 5th centuries BCE around the Greek-speaking Mediterranean.
They initiated systematic speculation about the underlying principle (arche) of reality.
- Thales of Miletus (c. 624-546 BCE) proposed water as the fundamental substance — the first known attempt at a naturalistic, non-mythological cosmology.
- Anaximander (c. 610-546 BCE) introduced the apeiron — the boundless or indefinite — as the source from which determinate things arise and to which they return.
- Anaximenes (c. 586-526 BCE) proposed air as the basic stuff, with condensation and rarefaction explaining qualitative variety.
- Pythagoras (c. 570-495 BCE) and the Pythagorean school held that number is the principle of all things, anticipating both mathematical Platonism and the structural conception of reality.
- Heraclitus of Ephesus (c. 535-475 BCE) emphasized flux: “everything flows” (panta rhei). His doctrine of the unity of opposites and the logos as cosmic ordering principle stands in sharp contrast to Parmenides.
- Parmenides of Elea (c. 515-450 BCE) in his poem On Nature argued that being is one, indivisible, and changeless; change and plurality are illusions.
- The Eleatic challenge — how can change be real if being cannot come from non-being? — drove subsequent metaphysics.
- Zeno of Elea (c. 490-430 BCE), Parmenides’s student, formulated the famous paradoxes (Achilles and the tortoise, the arrow, the dichotomy) defending Parmenidean monism.
- Empedocles (c. 494-434 BCE) responded with four roots (earth, water, air, fire) combined and separated by Love and Strife.
- Anaxagoras (c. 500-428 BCE) posited an infinite plurality of qualitatively distinct seeds, with Nous (mind) as the ordering principle.
- Democritus (c. 460-370 BCE) and Leucippus developed atomism.
- For the atomists, reality consists of indivisible atoms moving in the void.
- Qualitative differences reduce to atomic shape, size, and arrangement.
- This is the most enduring ancient anticipation of modern physical theory.
Plato
Plato (c. 428-348 BCE) developed the Theory of Forms (or Ideas) across the middle dialogues.
The key works are Phaedo, Republic, Symposium, and Phaedrus.
He revised the theory critically in late works like Parmenides and Sophist.
The Forms are non-spatial, non-temporal, mind-independent universals.
They are archetypes of which sensible particulars are imperfect copies.
Justice itself, beauty itself, the equal itself — these exist in a separate intelligible realm accessible only to reason.
The Form of the Good occupies the highest position.
It is analogous to the sun in the famous Cave Allegory of Republic 514a-520a.
In that allegory, prisoners chained in a cave mistake shadows for reality until one ascends to see the sun.
Plato’s metaphysics involves a strict ontological hierarchy: Forms > mathematical objects > sensible things > images.
Knowledge (episteme) attaches only to Forms; sensible things admit only opinion (doxa).
The participation relation between particulars and Forms — captured in the third man argument of Parmenides — remained a problem Plato himself recognized.
Aristotle
Aristotle (384-322 BCE) developed an alternative metaphysics.
The fourteen books later compiled as Metaphysics contain the bulk of his metaphysical work.
He rejected the separation of Forms, holding that universals exist in their instances (universalia in re).
The four causes from Physics II.3 and Metaphysics V.2 give a complete causal account of any substance:
- Material cause — what something is made of (bronze, for a statue)
- Formal cause — what it is to be that thing (the shape, for a statue)
- Efficient cause — what brings it about (the sculptor)
- Final cause — that for the sake of which (display, honor)
The doctrine of hylomorphism holds that every concrete substance is a compound of matter (hyle) and form (morphe).
Form makes a thing what it is; matter is what undergoes change.
The bronze sphere has form (sphericity) and matter (bronze).
When melted and recast as a cube, the matter persists and the form changes.
The distinction between actuality (energeia) and potentiality (dynamis) explains change without violating Parmenidean strictures.
What changes passes from potential to actual being.
An acorn is potentially an oak; the seed potentially a plant.
The Categories enumerates ten highest kinds under which any predicate falls.
These are substance, quantity, quality, relation, place, time, position (situs), state (habitus), action, and affection (passion).
Substance (ousia) is primary — what exists in its own right rather than predicated of something else.
Socrates is a primary substance; “human” is a secondary substance (a kind).
Aristotle’s Metaphysics XII (Lambda) introduces the Unmoved Mover.
The Unmoved Mover is pure actuality, eternal, immaterial, engaged in thinking of thinking (noesis noeseos).
It is the final cause of all motion in the cosmos.
This argument was enormously influential in medieval theology.
Medieval metaphysics
The medieval period synthesized Greek metaphysics with Abrahamic theology.
The major problems concerned the existence and attributes of God, the relation of essence to existence, the status of universals, and individuation.
Anselm and the ontological argument
Anselm of Canterbury (1033-1109) formulated the ontological argument in Proslogion (1077-1078).
His definition of God: “that than which nothing greater can be conceived.”
Since existence in reality is greater than existence in the mind alone, God must exist in reality.
Gaunilo’s “Lost Island” objection followed almost immediately.
Aquinas, Kant, and many moderns rejected the argument.
Descartes, Leibniz, and Plantinga have offered defenses.
Avicenna
Avicenna (Ibn Sina, 980-1037) developed the distinction between essence and existence.
What a thing is (its essence or quiddity) is distinct from that it is (its existence).
For all creatures, existence is added to essence.
Only in God are essence and existence identical.
This distinction became central to scholastic metaphysics.
Maimonides
Moses Maimonides (1138-1204) in Guide for the Perplexed (1190) addressed the relation between Aristotelian metaphysics and Jewish theology.
He defended negative theology — we can know what God is not, not what God is.
Aquinas and the Five Ways
Thomas Aquinas (1225-1274) in the Summa Theologiae (1265-1274) Part I, Question 2, Article 3, formulated the Five Ways:
- From motion: anything moved is moved by another; regress requires a first mover.
- From efficient causation: nothing causes itself; the causal chain requires a first cause.
- From contingency: contingent beings require a necessary being.
- From gradation: degrees of perfection require a maximally perfect being.
- From design (governance): the directedness of natural processes requires an intelligent director.
Scotus and haecceity
John Duns Scotus (1266-1308) introduced haecceity (thisness) as the principle of individuation.
What makes Socrates this particular human (and not just a human) is a non-qualitative individual essence.
He also developed the doctrine of the univocity of being against Aquinas’s analogy of being.
Ockham and nominalism
William of Ockham (c. 1287-1347) defended nominalism: universals are merely names or concepts, with only individuals existing in reality.
His razor — entities should not be multiplied beyond necessity — became a standard methodological principle.
The problem of universals
The medieval problem of universals divided three camps.
- Extreme realism (Plato) — universals exist independently of instances.
- Moderate realism (Aquinas) — universals exist in their instances.
- Conceptualism — universals exist in the mind.
- Nominalism (Ockham) — universals are mere names.
Modern metaphysics
Descartes
René Descartes (1596-1650) in Meditations on First Philosophy (1641) sought indubitable foundations.
The method of doubt yielded the cogito: “cogito, ergo sum” — I think, therefore I am — established in Meditation II.
The argument proceeds: even if I am being deceived by an evil demon, I must exist to be deceived.
Descartes then argued for substance dualism.
The mind (res cogitans) is an unextended thinking thing.
The body (res extensa) is an extended unthinking thing.
These are distinct substances capable of independent existence.
The interaction problem — how an immaterial mind causes physical motion — was raised by Princess Elisabeth of Bohemia and remained a central difficulty.
Descartes also revived the ontological argument in Meditation V, arguing that existence is a perfection contained in the idea of a perfect being.
Spinoza
Baruch Spinoza (1632-1677) in Ethics (1677, published posthumously) developed substance monism in geometric form.
Definition: a substance is what is in itself and conceived through itself.
From the definition follows that there can be only one substance, infinite in attributes, identifiable as God or Nature (Deus sive Natura).
Finite things are modes of this single substance.
Spinoza’s two known attributes — thought and extension — express the one substance under different aspects (the doctrine of parallelism).
Every mode of extension has a corresponding mode of thought.
Leibniz
Gottfried Wilhelm Leibniz (1646-1716) in the Monadology (1714) posited that ultimate reality consists of monads.
Monads are simple, indivisible, immaterial substances.
Monads are “windowless” (do not interact causally) but mirror the universe from their perspective.
This mirroring is arranged by God in pre-established harmony.
The principle of the identity of indiscernibles holds: if x and y share all properties, then x = y.
The converse principle of the indiscernibility of identicals also holds.
Together these are called Leibniz’s Law.
Leibniz also formulated the principle of sufficient reason: for every fact, there is a sufficient reason why it is so and not otherwise.
British empiricism
John Locke (1632-1704) in An Essay Concerning Human Understanding (1690) distinguished primary from secondary qualities.
Primary qualities (solidity, extension, motion, shape, number) are really in objects.
Secondary qualities (color, sound, taste) are powers in objects to produce sensations in us.
Locke held a corpuscular metaphysics influenced by Boyle.
George Berkeley (1685-1753) in A Treatise Concerning the Principles of Human Knowledge (1710) argued for immaterialism.
His central thesis: esse est percipi — to be is to be perceived.
There is no mind-independent matter; only minds and ideas exist.
God perceives everything continuously, securing the existence of unperceived (by us) objects.
David Hume (1711-1776) in A Treatise of Human Nature (1739-1740) and An Enquiry Concerning Human Understanding (1748) advanced a thoroughgoing skepticism.
Causation is reduced to constant conjunction plus a habit of mind expecting the effect.
We never perceive a necessary connection.
The self is a bundle of perceptions, with no underlying substantial soul (“bundle theory”).
The is/ought gap from Treatise III.1.1 holds that no normative conclusion follows from purely descriptive premises.
This gap became foundational for meta-ethics.
Kant
Immanuel Kant (1724-1804) in Critique of Pure Reason (1781, second edition 1787) attempted to synthesize rationalism and empiricism through transcendental idealism.
The mind imposes structure on experience through a priori categories (substance, causation, unity) and forms of intuition (space, time).
Key distinctions:
- A priori vs a posteriori — knowable independent of experience vs requiring experience
- Analytic vs synthetic — predicate contained in subject vs not
Kant claimed synthetic a priori judgments exist.
Examples include “7 + 5 = 12” and “every event has a cause.”
These judgments, he held, explain how mathematics and pure natural science are possible.
The phenomena/noumena distinction is central.
We know things only as they appear (phenomena), structured by our cognitive apparatus.
Things-in-themselves (noumena, Dinge an sich) lie beyond knowledge.
The Transcendental Dialectic shows that pure reason generates antinomies — contradictions about cosmology, theology, freedom — when it transgresses experience.
Hegel
Georg Wilhelm Friedrich Hegel (1770-1831) in Phenomenology of Spirit (1807) developed Absolute Idealism.
Reality is Spirit (Geist) coming to self-consciousness through a dialectical process.
The dialectic — often summarized as thesis/antithesis/synthesis (Fichte’s terminology, not Hegel’s preferred Aufhebung) — describes how concepts generate their opposites and are sublated into higher unities.
The Science of Logic (1812-1816) presents the categorial system from being and nothing through becoming up to the absolute idea.
Contemporary metaphysics
The 20th-century revival of metaphysics, after the logical positivist hostility, was largely driven by Quine, Strawson, Kripke, and David Lewis.
Quine and ontological commitment
W. V. O. Quine in “On What There Is” (1948, Review of Metaphysics) formulated the criterion of ontological commitment.
His slogan: “to be is to be the value of a variable.”
A theory is committed to those entities its quantifiers must range over.
This shifted the question from “what exists?” to “what must our best theories say exists?”
Quine famously defended an austere ontology of concrete particulars and sets, rejecting properties as universals.
Descriptive vs revisionary metaphysics
P. F. Strawson in Individuals: An Essay in Descriptive Metaphysics (1959) distinguished two enterprises.
Descriptive metaphysics seeks to describe the actual structure of our conceptual scheme.
In Strawson’s view, persons and material bodies are basic particulars.
Revisionary metaphysics seeks to revise that structure.
Strawson defended a descriptive program.
He argued that persons are basic individuals to which both physical and mental predicates are applied.
Modal metaphysics
Saul Kripke’s Naming and Necessity (1980, originally lectures 1970) transformed modal metaphysics.
Names are rigid designators — they pick out the same individual in every possible world in which that individual exists.
Natural kind terms like “water” and “gold” are also rigid.
These terms refer to whatever has the underlying nature (H₂O, atomic number 79).
This led to necessary a posteriori truths: “water is H₂O” is necessary but knowable only empirically.
Hilary Putnam’s Twin Earth thought experiment (1975) reinforced semantic externalism.
On a planet where the watery stuff is XYZ rather than H₂O, the word “water” refers to XYZ.
Meanings depend on the environment, not just internal mental states.
David Lewis in On the Plurality of Worlds (1986) defended modal realism.
Possible worlds are concrete, causally isolated universes existing on a par with the actual world.
“Actual” is indexical — pointing to whichever world the speaker inhabits.
Counterpart theory replaces transworld identity.
I exist in this world; counterparts of me exist in others.
The ontological cost was enormous.
Most philosophers prefer ersatz approaches treating possible worlds as abstract objects (Plantinga, Stalnaker, Adams).
Mereology and composition
Mereology — the formal theory of part-whole relations — originated with Stanisław Leśniewski (1916).
It was extended by Henry Leonard and Nelson Goodman in “The Calculus of Individuals” (1940).
Classical mereology accepts unrestricted composition: any plurality has a fusion.
Peter van Inwagen’s Material Beings (1990) raised the Special Composition Question.
When do some things compose a further thing?
Answers span:
- Nihilism — only simples exist; no composites
- Universalism — any collection composes something
- Moderate views — only living organisms (van Inwagen), only objects with the right cohesion
Theodore Sider’s Writing the Book of the World (2011) defends a metaphysics centered on structure and the notion of fundamentality.
He argues that some quantifiers and predicates are joint-carving and others not.
Universals, tropes, and bundles
The problem of universals — what accounts for qualitative similarity — admits several positions.
- Realism in re (Aristotle, Armstrong) — universals exist in their instances.
- D. M. Armstrong’s A Theory of Universals (1978) and Universals: An Opinionated Introduction (1989) defend a scientific realism about universals as immanent.
- Realism ante rem (Plato) — universals exist independently of instances.
- Nominalism — only particulars exist.
- Variants of nominalism include predicate nominalism, concept nominalism, class nominalism, and resemblance nominalism.
- Trope theory (D. C. Williams 1953, Keith Campbell Abstract Particulars 1990) — properties are particularized instances (this redness, not redness).
- Ordinary objects on this view are bundles of compresent tropes.
- Bundle theory — objects are bundles of properties or tropes, with no underlying substratum.
- Substratum theory — objects consist of a propertyless bare particular instantiating properties.
Time and tense
J. M. E. McTaggart in “The Unreality of Time” (Mind 1908) distinguished the A-series from the B-series.
The A-series uses past/present/future, with tense.
The B-series uses earlier/later, tenseless.
McTaggart argued both lead to contradiction.
Contemporary positions:
- Presentism — only the present is real (Prior, Bigelow, Markosian)
- Eternalism — past, present, and future are equally real (block universe, 4D)
- Eternalism is favored by interpretations of special relativity.
- Growing block — past and present are real, future is not (Broad, Tooley)
- Moving spotlight — eternalism plus an objective present that moves
Hilary Putnam in “Time and Physical Geometry” (1967) argued that special relativity is incompatible with presentism.
Simultaneity is relative, so no privileged present exists.
Causation
Theories of causation:
- Regularity theory (Hume) — causation is constant conjunction
- Counterfactual (David Lewis, “Causation” 1973) — c causes e iff, had c not occurred, e would not have occurred (in possible worlds with closest similarity)
- Probabilistic (Cartwright, Suppes) — causes raise the probability of their effects
- Interventionist / manipulationist (Woodward, Making Things Happen 2003) — c causes e iff intervening on c changes e
- Mechanistic (Glennan, Machamer-Darden-Craver MDC 2000) — causation requires productive mechanisms
Free will
Three main positions on the metaphysics of free will:
- Hard determinism — determinism is true, so no free will (d’Holbach, Inwagen’s incompatibilist consequence argument)
- Libertarianism — free will exists and is incompatible with determinism (Chisholm’s agent causation, Robert Kane’s The Significance of Free Will 1996)
- Compatibilism — free will is compatible with determinism (Hume; Harry Frankfurt’s “Freedom of the Will and the Concept of a Person” 1971 hierarchical theory of higher-order desires; Daniel Dennett’s Elbow Room 1984 and Freedom Evolves 2003)
Frankfurt cases (1969) challenged the principle of alternate possibilities.
An agent can be morally responsible even when she could not have done otherwise.
Laws of nature
- Humean supervenience (David Lewis) — laws supervene on the total mosaic of local matters of particular fact.
- The Best System account holds that laws are theorems of the deductively closed system that best balances simplicity and strength.
- Necessitarian (Armstrong What Is a Law of Nature? 1983, Tooley, Dretske) — laws are second-order relations of necessitation between universals.
- Dispositional essentialism (Bird, Ellis, Mumford) — laws derive from the essential dispositions of properties.
- Tim Maudlin’s The Metaphysics Within Physics (2007) defends laws as fundamental ontological items.
Realism vs anti-realism
Michael Dummett (1925-2011) reformulated realism debates in semantic terms.
Realism about a domain is the view that statements about that domain are determinately true or false independently of our means of knowing them (preserves bivalence).
Anti-realism rejects this.
Dummett applied the framework to mathematics, the past, other minds, and ethics.
In philosophy of science, Bas van Fraassen’s The Scientific Image (1980) advocates constructive empiricism.
Science aims at empirical adequacy, not truth about unobservables.
John Worrall’s structural realism (“Structural Realism: The Best of Both Worlds?” Dialectica 1989) holds that we know only the structure described by scientific theories, not the underlying nature.
Ladyman and Ross’s Every Thing Must Go (2007) defends ontic structural realism: structure is all there is.
Persistence and identity
Diachronic identity — how things persist through time — admits three views.
- Endurance (3D) — objects are wholly present at each moment they exist
- Perdurance (4D) — objects are extended through time as well as space, with temporal parts
- Exdurance (stage theory, Sider, Hawley) — objects are momentary stages; “the same” object at different times is a counterpart relation
The Ship of Theseus thought experiment — gradually replacing every plank — challenges identity.
Locke’s psychological continuity criterion of personal identity in Essay II.27 (1694) was criticized by Thomas Reid (1785) with the brave officer paradox.
Derek Parfit’s Reasons and Persons (1984) defended a reductionist view.
Personal identity is not what matters; what matters is psychological continuity.
Psychological continuity can branch and fail to be one-one.
Eric Olson’s The Human Animal (1997) defends animalism: we are human animals, identity tracked by biological life, not psychology.
Modality continued — necessity and essentialism
Necessity de re concerns properties an individual must have to be that individual.
Necessity de dicto concerns propositions that must be true.
Origin essentialism (Kripke) holds that an individual could not have had a different origin than the one it actually had.
A given table necessarily originated from the particular piece of wood from which it came.
ESS essentialism extends this to other essential properties.
Plantinga (The Nature of Necessity 1974) and Stalnaker offer ersatz views of possible worlds as maximal consistent sets of propositions or maximal states of affairs.
This avoids Lewis’s ontological commitments while retaining the formal benefits of possible-worlds semantics.
Grounding and dependence
Grounding — the relation of metaphysical dependence weaker than identity but stronger than supervenience — has become a major topic.
Fine’s “Guide to Ground” (2012) and Schaffer’s “On What Grounds What” (2009) give it formal treatment.
The grounding relation is typically taken to be irreflexive, asymmetric, and transitive.
Examples: physical facts ground mental facts, microphysical facts ground macrophysical facts, conjunctive facts are grounded in their conjuncts.
The notion is invoked to articulate priority monism (Schaffer): the cosmos as a whole is fundamental, with its parts derivative.
Recent developments
The early 21st century has seen a proliferation of work in metaphysics.
Key figures include Kit Fine (essence, ground), Karen Bennett (composition, grounding), Jonathan Schaffer (priority monism), L. A. Paul (experience, decision under transformative experience), Helen Beebee (Humeanism), Trenton Merricks (object-restricted ontology), and Achille Varzi (mereology).
L. A. Paul’s Transformative Experience (2014) raises questions about rational decision-making under conditions where one cannot know in advance what an experience will be like.
Karen Bennett’s Making Things Up (2017) systematizes the family of building relations including grounding, composition, and realization.
Object-oriented ontology (OOO), associated with Graham Harman’s Tool-Being (2002) and the speculative realist movement (Meillassoux’s After Finitude 2008), reacts against post-Kantian correlationism.
It defends the autonomy of objects from human access.
Non-Western contributions
The library will also catalog non-Western metaphysical traditions in later notes.
These include Indian metaphysics (Nyaya substance ontology, Buddhist anatman and dependent origination, Advaita Vedanta non-dualism), Chinese metaphysics (Daoist process thought, Neo-Confucian li and qi), and Islamic philosophy (Mulla Sadra’s existential metaphysics, Sufi ontology).
Comparative metaphysics is an active area of current scholarship.
Methods in contemporary metaphysics
Contemporary metaphysics employs several distinctive methods.
Conceptual analysis dissects a concept by tracing entailments and counterexamples.
Reflective equilibrium balances intuitions against principles.
Thought experiments — twin earth, swampman, brain in a vat — test modal claims.
Formal modeling uses possible-worlds semantics, set theory, mereology, and modal logic.
Empirically informed metaphysics draws on results from physics, neuroscience, and cognitive science.
The dispute over metaphysics’s relation to empirical science divides naturalists (Quine, Ladyman) from autonomists (Lowe, Fine).
Recent topical trends
The 2010s and 2020s have seen growing interest in social ontology.
John Searle’s The Construction of Social Reality (1995), Margaret Gilbert’s Joint Commitment (2014), Brian Epstein’s The Ant Trap (2015), and Sally Haslanger’s work address the ontology of money, marriage, race, gender, institutions.
Philosophy of race specifically: Haslanger’s “Gender and Race: (What) Are They? (What) Do We Want Them To Be?” (Nous 2000) defends social constructionism about race.
Quentin Meillassoux’s After Finitude (2008) attacks correlationism — the post-Kantian view that thought and being are correlatives.
The vague-objects debate continues: are there vague entities in the world, or only vague representations?
Gareth Evans’s “Can There Be Vague Objects?” (Analysis 1978) argued not; Terence Parsons Indeterminate Identity (2000) argues for vague identity.