Seventeenth-century Europe is marked by the rise of mathematical science and the modern nation-state. The former facilitates the naturalization of human psychology. The latter forces rethinking political sovereignty through social contract theories. But as the faculties of mind are reduced to bodily affects, traditional ethics is threatened: reason no longer clearly rules the passions; if political reason is dissolved into affective undercurrents, the constitution turns out to rest on illusion. This thesis argues that Spinoza embraces the consequences of the naturalization of reason, contrasting his views with elements in Descartes’ Passions of the Soul and Hobbes’ Leviathan.