The article proposes a new solution to the long-standing problem of the universality of essences in Spinoza's ontology. It argues that, according to Spinoza, particular things in nature possess unique essences, but that these essences coexist with more general, mind-dependent species-essences, constructed by finite minds on the basis of similarities that obtain among the properties of formally-real particulars. This account provides the best fit both with the textual evidence and with Spinoza's other metaphysical and epistemological commitments. The article offers new (...) readings of how Spinoza understands not just the nature of essence, but also the nature of being, reason, striving, definitions, and different kinds of knowledge. (shrink)