Part III of Spinoza's
Ethica, ordine geomterico demonstrata (
Ethics demonstrated in geometrical order) concerns the ‘nature and origin of the affects’ (roughly, emotions) and consists chiefly of a long series of arguments to the effect that, in thus-and-such circumstances, we will,
ceteris paribus, be excited with this or that affect: when, for example, ‘anyone conceives that he is loved by another, and believes that he has given no cause for such love, he will love that other in return’ (Prop. XLI), and ‘love or hatred towards a thing, which we conceive to be free, must, other conditions being similar, be greater than if it were felt towards a thing acting by necessity’ (Prop. XLIX). In the process of defending these theses, Spinoza takes himself to be providing a scientific (cause-to-effect) account of the essences of our various affects, and thus ascertaining their real, as opposed to merely nominal, definitions.