Substance — That which exists by itself, without depending on anything else in order to subsist, and which serves as the bearer of the attributes or qualities predicated of it. The Latin substantia literally means “that which stands underneath,” translating Aristotle’s Greek ousia, sometimes linked to the hypokeimenon, the “substratum” that persists through change. In the Categories, Aristotle distinguishes primary substance — the concrete individual, such as this man named Socrates — from secondary substance, the species or genus (man, animal) under which the individual is classified. Primary substance is the ultimate subject of all predication: qualities, quantities, and relations are said of it, but it is said of no further subject. In the modern period the concept branches in divergent directions. Descartes admits three substances: God (infinite and self-subsisting), mind (res cogitans, whose essence is thought), and matter (res extensa, whose essence is extension). Spinoza, pressing to its limit the definition of substance as that which exists in itself and is conceived through itself, concludes that there can be only one infinite substance — God or Nature (Deus sive Natura) — of which everything else is merely a mode or affection. Leibniz, by contrast, multiplies substances into infinitely many monads, simple, immaterial units without parts. The concept is closely bound up with that of accident (the quality that does not subsist on its own) and that of essence (what makes a thing be what it is).
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