The Identity of Indiscernibles and Human Essence in Spinoza’s Ethics

Abstract Spinoza denies at E1p5, on the basis of the Principle of the Identity of Indiscernibles, that two different substances can have the same nature. He argues at E1p8s2 and E2p10s that different human beings do have the same nature and that this justifies the conclusion that human beings are not substances. I argue that these commitments, together with further commitments in moral psychology and ethics, suggest that on Spinoza’s view human nature is real and that it is a single thing, which is a component of each individual human being. Where Spinoza writes that to the extent that human beings live from reason we agree in nature (E4p35), he means that in so acting we are one thing.