Substance
substratum
What a thing fundamentally is, as against the properties it happens to have. Aristotle's ousia is the bearer that persists through change; Descartes defined it as what needs nothing else in order to exist, and Spinoza showed that definition admits exactly one instance.
In practice
Every claim that a business is 'still the same company' after its staff, product and owners have all changed is a claim about substance. So is every claim that a person is the same person after a conversion or a collapse.
The common mistake
Assuming the concept is technical and idle. It is the machinery behind personal identity, the persistence of institutions, the mind-body problem and the doctrine of the Eucharist, and Hume's argument that there is no such thing has never been comfortably answered.
Something persists while its properties change. The chair is repainted and remains that chair; you are not the person you were and are nonetheless that person. Substance is the name for whatever does the persisting, and the long argument is over whether there is any such thing or only the properties.
Aristotle, and the unresolved shift
The Categories gives the doctrine that entered the tradition. Primary substance is the individual — this man, this horseAristotle, Categories 5, 2a11–19. Primary substance is what is neither said of a subject nor in a subject; species and genera are secondary substances. Everything else — quantity, quality, relation — exists in a subject and so depends on substance.; species and genera are secondary. Everything else exists in a subject and so depends on it. But in Metaphysics Z the answer changes: what is most properly substance is the form or essence rather than the composite individual. Reconciling the two texts is one of the standing problems of Aristotle scholarship, and the medieval tradition largely built on the second.
Scholastic philosophy developed the substance-accident distinction into a precise instrument, and it carried doctrinal weight: transubstantiation, defined at the Fourth Lateran Council in 1215 and given its Aristotelian articulation by Aquinas (Summa Theologiae III q. 75), holds that the substance of bread changes while the accidents remain. Whatever one makes of the doctrine, it is the clearest illustration of what the distinction was taken to permit.
Descartes to Spinoza: the definition eats itself
Descartes defined substance as that which requires nothing else in order to exist, then immediately conceded that strictly speaking only God satisfies itDescartes, R. (1644). Principles of Philosophy I.51. Having defined substance as what needs no other thing to exist, Descartes concedes the term applies univocally only to God, and is used of created things in a secondary sense — a concession Spinoza treated as fatal., and applied the term to thinking and extended things in a weaker sense. Spinoza (1677) refused the weaker sense: if substance is what is in itself and conceived through itself, there can be only one, and thought and extension are its attributes rather than separate substances. Descartes's dualism and Spinoza's monism follow from the same definition, which is the strongest evidence that something in the definition was unstable.
The objections
Locke (1689) allowed that we have no positive idea of substance, only the supposition of a substratum supporting the qualities we observe — 'something, he knows not what'. Hume (1739) drew the conclusion: every idea derives from an impression, there is no impression of a substance as distinct from its qualities, so there is no such idea. What we call an object is a bundle of co-occurring qualities, and what we call a self is a bundle of perceptions with nothing underneath.
Kant (1781) answered by relocating the concept: substance is not discovered in experience but is a category the understanding contributes, without which experience of an objective world would not be possible at all. Nietzsche later pressed the deflationary line further, arguing that the subject-predicate structure of Indo-European grammar generates the belief in a doer behind the deed — a diagnosis rather than a refutation, but one that has stuck.
What it rules out
It rules out treating identity over time as obvious. Something must persist for the claim to be true, and naming that thing is the entire difficulty. It rules out the assumption that a list of properties exhausts a description. And on Hume's account it rules out the self as a simple continuing thing, which is the conclusion most people find unbearable and few have refuted.
It does not rule out talking about objects and persons as persisting. Bundle theories explain the practice rather than abolishing it; what they remove is the substratum, not the chair.
Sources
Aquinas, T. (c. 1270). Summa Theologiae III, q. 75. · Aristotle. Categories 5; Metaphysics Z. · Descartes, R. (1644). Principles of Philosophy I.51–52. · Hume, D. (1739). A Treatise of Human Nature I.4.3, I.4.6. · Kant, I. (1781). Critique of Pure Reason, First Analogy. · Locke, J. (1689). An Essay Concerning Human Understanding II.23. · Nietzsche, F. (1888). Twilight of the Idols, 'Reason in Philosophy'. · Spinoza, B. (1677). Ethics, Part I.
Concept web
Open the full webQuestions
What is substance in philosophy?
What a thing fundamentally is, as against the properties it happens to have — the bearer that persists through change. Aristotle called it ousia and took primary substance to be the individual thing.
What is the difference between substance and accident?
Substance is what exists in its own right; accidents are properties that exist only in a subject — colour, size, position. The scholastic development of the distinction is what makes the doctrine of transubstantiation statable.
Why did Spinoza say there is only one substance?
Because he took Descartes's definition literally. If substance is what is in itself and conceived through itself, nothing finite qualifies — Descartes had already conceded only God strictly satisfies it — so there is one substance, and thought and extension are its attributes.
Did Hume reject substance?
Yes. Every idea derives from an impression, and there is no impression of substance apart from its qualities, so there is no such idea. An object is a bundle of co-occurring qualities and the self a bundle of perceptions — A Treatise of Human Nature I.4.