Abstract
Nature, as Spinoza conceives of it, contains individual things or finite modes, each with its own essence. Although we humans classify individuals into kinds, Spinoza is adamant that the resulting types or species “are nothing”. Despite Spinoza's nominalism, his mature works posit differences between animal kinds that are discoverable by reasoning and available to philosophical understanding. Spinoza's world is fluid in the sense that the powers of individuals are in flux, changing as they interact with one another. In Spinoza's view, changes in an individual's power are typically the effects of its interactions with external things. Spinoza contrasts the affective dynamics between human natures with a lack of affective commonality between humans and other kinds of animals. In his political works Spinoza translates his account of natures or essences into juridical terms. The claim that mutual sociability is what makes an animal kind is of a piece with the rest of Spinoza's philosophy.