Monad (monade, from Greek monás, “unit”) — In Leibniz, a simple substance without parts, constituting the ultimate and truly real element of composite things. The word comes from the Greek monás, “unity,” used by the Pythagoreans and revived in the Renaissance by Giordano Bruno (De monade, 1591). In the Monadology (written in 1714 and first published in 1720, in a German translation), Leibniz argues that if there are composites there must be simples; monads, having no parts, have no extension, shape, or divisibility, and can begin only by creation and end only by annihilation. They “have no windows” (§ 7): nothing can enter or leave them, so they do not interact causally. Each monad is nevertheless endowed with perception, which expresses the entire universe from its own point of view, and with appetition, the tendency leading it from one perception to another (§§ 14-15). The agreement among monads, and between soul and body, is explained by the pre-established harmony instituted by God, the supreme or primitive monad (§ 47). The doctrine responds to Cartesian dualism, which Leibniz considers unable to explain the unity of substances, and to Spinoza’s monism, against which he sets a plurality of individual substances. It is also a theory that ultimate reality is not material: bodies are well-founded phenomena grounded in monads. See Leibniz, Giordano Bruno, Spinoza, Descartes, and substance.
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