In this essay, I claim that certain passages in Book IV of Benedict de Spinoza’s Ethics suggest a novel version of what is known as metaethical constructivism. The constructivist interpretation emerges in the course of attempting to resolve a tension between Spinoza’s apparent ethical egoism and some remarks he makes about the efficacy of collaborating with the right partners when attempting to promote our individual self-interest . Though Spinoza maintains that individuals necessarily aim to promote their self-interest, I argue that (...) Spinoza has an atypical conception of self that allows the interests of other people to be partially constitutive of one's own self-interest. In this way, Spinoza can account for the rationality of concern for the interests of others . This interpretation attributes to Spinoza a form of constructivism that differs in important ways from contemporary Humean and Kantian constructivisms and which can in principle be detached from Spinoza’s particular metaphysical commitments in order to yield a third general category of constructivist view . Though my treatment is necessarily brief, it is my hope that it can serve both to motivate a constructivist reading of Spinoza and, perhaps even more crucially, to suggest a Spinozistic variety of constructivism as a live theoretical option in metaethics. (shrink)