<ontology, epistemology, causality, necessity, empiricism> technically (for Leibniz, Spinoza, Descartes, et. al.) - a self-subsistent entity or thing, not depending on anything (except, possibly God) for its existence: also, the ultimate bearer of attributes or properties. In a somewhat looser sense (closer to Aristotle's) "substance" is used to refer to the individuals which are the bearers of attributes or havers of properties as opposed to the attributes or properties - universals - that they have or which inhere in them.
<philosophical terminology> what a thing is made of; hence, the underlying being that supports, exists independently of, and persists through time despite changes in, its accidental features. Aristotle identified substance - both primary and secondary - as the most fundamental of the ten categories of being. According to Spinoza, there can be no more than one truly independent being in the universe. Recommended Reading: Mary Louise Gill, Aristotle on Substance (Princeton, 1991); Charlotte Witt, Substance and Essence in Aristotle (Cornell, 1994); R. S. Woolhouse, Descartes, Spinoza, Leibniz: The Concept of Substance in Seventeenth-Century Metaphysics (Routledge, 1993); Jeffrey Edwards, Substance, Force, and the Possibility of Knowledge: On Kant's Philosophy of Material Nature (California, 2000); Joshua Hoffman and Gary S. Rosenkranz, Substance: Its Nature and Existence (Routledge, 1996); Anthony Quinton, The Nature of Things (Routledge, 1993); and David Wiggins, Sameness and Substance Renewed (Cambridge, 2001).
[A Dictionary of Philosophical Terms and Names]
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