Leibniz

Substance

Leibniz was dissatisfied with the way Descartes and Spinoza had described the nature of substance, because he felt they had distorted our understanding of human nature, freedom, and the nature of God. To say, as Descartes did, that there are two independent substances, thought and extension, was to produce the impossible dilemma of trying to explain how those two substances could interact as body and mind either in humanity or in God. Spinoza had tried to solve the dilemma by saying that there is only one substance with two knowable attributes, thought and extension. But to reduce all reality to a single substance was to lose the distinction between the various elements in nature. To be sure, Spinoza spoke of the “world” as consisting of many “modes,” in which the attributes of thought and expression appear. Still, Spinoza’s monism was a pantheism in which God was everything and everything was part of everything else. To Leibniz, this conception of substance was inadequate because it blurred the distinctions among God, humanity, and nature, each of which Leibniz wanted to keep separate. Paradoxically, Leibniz accepted Spinoza’s single-substance theory and his mechanical model of the universe but presented such a unique theory of this one substance that he was able to speak of the individuality of persons, the transcendence of God, and the reality of purpose and freedom in the universe.

 Extension versus Force

Leibniz challenged the fundamental assumption upon which Descartes and Spinoza had built their theory of substance, namely, that “extension” implies actual size and shape. Descartes assumed that “extension” refers to a material substance that is extended in space and is not divisible into something more primary. Spinoza, too, considered extension as an irreducible material attribute of God or Nature. Leibniz disagreed. Observing that the bodies or things we see with our senses are divisible into smaller parts, why can we not assume, asks Leibniz, that all things are compounds or aggregates? “There must be,” he said, “simple substances, since there are compound substances, for the compound is only a collection or aggregatum of simple substances.”

There is nothing new in saying that things must be made of simple substances, for Democritus and Epicurus had argued centuries before that all things consist of small atoms. But Leibniz rejected this notion of atoms, because Democritus had described these atoms as extended bodies, as irreducible bits of matter. Such a particle of matter would have to be considered lifeless or inert and would have to get its motion from something outside itself. Rejecting the idea of matter as primary, Leibniz argued that the truly simple substances are the monads, and these are “the true atoms of nature … the elements of things.” The monads differ from atoms in that atoms were viewed as extended bodies, whereas Leibniz described the monad as being “force” or “energy.” Leibniz therefore said that matter is not the primary ingredient of things but that monads with their element of force constitute the essential substance of things.