Substance in Philosophy: From Aristotle to Heidegger — History of a Fundamental Concept

Few concepts have traversed the history of Western philosophy with such persistence — and so many metamorphoses — as substance. From the Greek ousia to the Latin substantia, from Aristotelian form to the Leibnizian monad, from Cartesian res cogitans to Locke’s unknown substratum, this term has served as the axis for the most decisive metaphysical questions: What truly exists? What persists through change? What is a thing apart from its properties?

This article traces the trajectory of the concept of substance from Aristotle to its radical questioning in contemporary philosophy, examining how each great philosophical system redefined, expanded, or challenged it.

1. Aristotle: the foundation of the concept

1.1 Ousia in the Categories

The starting point is Aristotle (c. 384–322 BC). In the Categories, he distinguishes primary substance (protē ousia) from secondary substance (deutera ousia). Primary substance is the concrete individual — this man, this horse — that which is neither predicated of any subject nor exists in any subject. It is the ultimate substrate of all predication: we say that Socrates is a man, is white, is sitting, but Socrates himself is not predicated of anything.

Secondary substance designates the species and genera under which primary substance is classified: “man” and “animal” are secondary substances of Socrates. They say what the primary substance is, but they do not exist independently of individuals.

The remaining categories — quantity, quality, relation, place, time, position, possession, action, passion — are accidents: they exist only in a substance. Whiteness exists in Socrates; without Socrates (or some other substrate), whiteness does not subsist on its own.

1.2 Ousia in the Metaphysics: hylomorphism

In the Metaphysics (especially the central books Ζ, Η, and Θ), Aristotle reformulates and deepens the concept. Now substance is analysed in terms of matter (hylē) and form (morphē/eidos) — the doctrine of hylomorphism. The concrete substance — the synolon — is the composite of matter and form. A bronze statue is bronze (matter) organized according to a specific configuration (form).

Aristotle wavers among different candidates for the title of primordial substance: matter (the substrate that receives all determinations), form (what makes a thing what it is), the composite, or essence (to ti ēn einai — “what it was to be” for something). In the central books of the Metaphysics, the predominant conclusion is that form is substance in the primary sense, for it is form that confers determination and intelligibility upon the being.

1.3 Act and potency

The doctrine of substance is articulated with the concepts of act (energeia) and potency (dynamis). Matter is potency — the capacity to receive forms; form is act — determinate realization. Motion (change) is the passage from potency to act. Substance in its fullest sense is pure act: the Unmoved Mover, thought thinking itself, is the supreme substance precisely because in it there is no potentiality whatsoever.

2. Scholasticism: substance, accidents, and transubstantiation

2.1 The Latin reception of Aristotle

When Aristotle’s works were translated into Latin in the twelfth and thirteenth centuries — often via Arabic versions by Avicenna and Averroes — the term ousia was rendered as substantia (literally, “that which stands under,” sub-stare). Medieval scholastics inherited and refined the distinction between substance and accidents, integrating it into the framework of Christian theology.

2.2 Thomas Aquinas: being, essence, and existence

Thomas Aquinas (1225–1274) accomplished the most ambitious synthesis of Aristotle and Christian thought. In On Being and Essence (De Ente et Essentia), he distinguishes essence (what a thing is) from existence (the fact that it is). In creatures, essence and existence are really distinct: the essence of a horse does not entail that it exists. Only in God do essence and existence coincide — God is ipsum esse subsistens, subsistent being itself, the pure act of existing.

Created substance is therefore a composite of essence and existence. Accidents — colour, size, position — depend on substance to exist, but are really distinct from it. This real distinction between substance and accidents enabled the philosophical formulation of the theological doctrine of transubstantiation: in the Eucharist, according to Catholic theology, the substance of the bread is converted into the substance of Christ’s body, while the accidents (appearance, taste, texture) remain unchanged. The Council of Trent (1545–1563) ratified this formulation, showing how a Greek philosophical concept found direct theological application.

2.3 Duns Scotus and Suárez

Other scholastics introduced important variations. Duns Scotus (c. 1266–1308) proposed that the concept of being is univocal — it is said in the same sense of God and creatures — against the Thomistic analogy. Francisco Suárez (1548–1617), in the Disputationes Metaphysicae, systematized scholastic metaphysics so thoroughly that he directly influenced modern philosophers: Descartes, Leibniz, and Wolff all read Suárez carefully.

3. Descartes: two substances

3.1 The Cartesian revolution

René Descartes (1596–1650) breaks with the Aristotelian-scholastic tradition but preserves the vocabulary of substance. In the Principles of Philosophy (1644, Part I, art. 51), he defines substance as that which exists in such a way that it needs no other thing to exist — a definition the Meditations on First Philosophy (1641) already presuppose, though without formulating it in those terms. In the strict sense, only God satisfies this definition. But in a derivative sense, there are two created substances radically distinct from one another:

• Res cogitans (thinking thing): the mind, whose essence is thought. It is indivisible, non-spatial, free.
• Res extensa (extended thing): body/matter, whose essence is extension in length, breadth, and depth. It is divisible, spatial, mechanical.

3.2 The problem of interaction

Cartesian dualism generates a celebrated problem: how can two substances of absolutely distinct natures — thought and extension — interact? How does the mind (immaterial) move the body (material)? Descartes attempted an answer by appealing to the pineal gland as the point of contact, but the solution was widely considered unsatisfactory. This “mind-body problem” mobilized all of seventeenth-century philosophy and determined the course of subsequent rationalist metaphysics.

4. Spinoza: the single substance

4.1 Deus sive Natura

Baruch Spinoza (1632–1677) resolves the Cartesian dualism by the most radical path: there is a single substance, which is God, that is, Nature (Deus sive Natura). In the Ethics Demonstrated in Geometrical Order (1677), he proceeds from rigorous definitions: substance is that which exists in itself and is conceived through itself, that is, that whose concept does not depend on the concept of another thing. Now, Spinoza demonstrates, there can be only one substance, for if there were two, one would limit the other, and neither would be truly infinite.

4.2 Attributes and modes

This single substance possesses infinite attributes, of which we know two: thought and extension. Thought and extension are therefore not two substances (as Descartes held), but two attributes of one and the same substance. All individual beings — minds and bodies — are modes, that is, finite modifications of the infinite substance. Socrates is not a substance: he is a mode of the divine substance under the attribute of thought (as mind) and under the attribute of extension (as body).

4.3 Consequences

Spinozan monism has radical consequences: there is no free will (everything happens by necessity), there is no personal God (God is not a being separate from the world but the world itself in its totality), and human freedom consists not in escaping necessity but in understanding it — acting from adequate internal causes rather than being driven by external passions.

5. Leibniz: monads as simple substances

5.1 Against monism

Gottfried Wilhelm Leibniz (1646–1716) agrees with Spinoza in rejecting Cartesian dualism, but refuses monism: substance cannot be one alone, because that annihilates the individuality of things. In the Monadology (1714), Leibniz proposes that reality is composed of infinitely many monads — simple, indivisible, immaterial substances, without parts and therefore “windowless” (nothing enters or leaves them through causal interaction).

5.2 Perception and pre-established harmony

Each monad is a centre of perception and appetition: it mirrors the entire universe from its own point of view, with greater or lesser degrees of clarity. The human monad (spirit) has clear and distinct perceptions; lower monads perceive confusedly. God, the Supreme Monad, created all the others and coordinated their internal states through a pre-established harmony: there is no real interaction between substances, but their states correspond because God programmed them to function in perfect synchrony.

5.3 Substance as force

For Leibniz, the essence of substance is not extension (as for Descartes) but force (vis). Substance is activity, entelechy — a term borrowed from Aristotle. Extended matter, by itself, is passive and inert; the true reality is the living force underlying corporeal appearance.

6. Locke: the unknown substratum

6.1 The empiricist critique

John Locke (1632–1704), in the Essay Concerning Human Understanding (1690), approaches substance from a radically different angle: the epistemological. Locke asks: where does our idea of substance come from? Not from direct experience, for we never perceive substance itself — we perceive only qualities (colours, shapes, weights). The idea of substance is therefore the idea of an unknown substratum, a “something, I know not what” that supposedly supports the qualities we actually perceive.

6.2 An obscure but unavoidable concept

Locke does not deny the existence of substance; he merely acknowledges that we have no clear and distinct idea of it. We do not know what substance is; we know only that there must be something serving as the support for observed qualities. This confession of ignorance prepares the ground for David Hume’s more radical critique and, ultimately, for the Kantian revolution.

7. Kant: substance as a category of the understanding

7.1 The Copernican revolution

Immanuel Kant (1724–1804) entirely reformulates the problem. In the Critique of Pure Reason (1781/1787), substance ceases to be a property of things in themselves and becomes a category of the understanding — an a priori form that the subject applies to experience to make it intelligible.

7.2 The First Analogy of Experience

In the section on the “Analogies of Experience,” Kant formulates the Principle of the Permanence of Substance: in all change of appearances, substance persists and its quantity in nature neither increases nor diminishes. This principle is not derived from experience (as Locke supposed) but is an a priori condition of the possibility of experience: we can perceive changes only if we presuppose something permanent underlying them. Without permanent substance, the very distinction between change and temporal succession would be impossible.

7.3 The limits of the concept

However, Kant rigorously restricts the scope of the concept: substance is legitimate only in the domain of phenomena — the world as it appears to us. We cannot apply it to the thing-in-itself (Ding an sich), the world as it is independently of our forms of perception and thought. Traditional metaphysics, which claimed to know supersensible substances (God, soul, the world as a totality), oversteps the limits of possible experience and falls into illusions — the antinomies and paralogisms of pure reason.

8. The abandonment of the concept in contemporary philosophy

8.1 Heidegger: the destruction of substance ontology

Martin Heidegger (1889–1976) undertakes a radical critique of the notion of substance. In Being and Time (1927), he argues that Western metaphysics, since Plato and Aristotle, has interpreted being as constant presence (ousia as parousia, permanence) — and this interpretation culminated in the notion of substance as a subsisting, stable, given thing. Heidegger calls this the forgetting of being: by reducing being to substance, the tradition obscured the more fundamental question — the ontological difference between being and beings.

The human mode of being — Dasein — cannot be understood as substance. Dasein is not a thing with properties; it is being-in-the-world, openness, care (Sorge), thrown projection. To think of the human being as a thinking substance (Descartes) is, for Heidegger, to relapse into the same metaphysics of presence that prevents understanding the radical temporality of existence.

8.2 Analytic philosophy: from substance to bundles of properties

In the analytic tradition, the concept of substance underwent a gradual erosion. Bertrand Russell and other logical empiricists revived the Humean critique: if substance is not observable, why posit it? The most influential alternative is the bundle theory: an object is not a substance that has properties, but simply a bundle of co-instantiated properties. There is no hidden substratum behind the whiteness, hardness, and spherical shape — the object is that set of qualities.

Other analytic philosophers — such as P.F. Strawson in Individuals (1959) — attempted to rehabilitate the notion of substance (or “basic particular”) as a condition of possibility for our conceptual scheme: we need substances (bodies and persons) to re-identify objects across time and construct a coherent discourse about the world.

8.3 Whitehead: from substantialism to process philosophy

Alfred North Whitehead (1861–1947), in Process and Reality (1929), replaced the ontology of substance with an ontology of process: ultimate reality is not constituted by permanent substances but by actual occasions — momentary events of creative self-constitution. Static substance yields to dynamic becoming.

9. The concept of substance in perspective

The history of the concept of substance is, in large measure, the history of Western metaphysics itself. Each redefinition marks a shift in philosophical paradigm:

From Aristotle to Heidegger, substance moved from unquestioned ontological foundation to a concept in need of overcoming. But even its dissolution attests to its centrality: understanding why contemporary philosophy abandoned substance requires understanding why, for two millennia, it seemed indispensable.

The concept of substance is not merely a chapter in the history of philosophy — it is the thread by which that history can be told.

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