Substance, nature, and necessity › Desire and the effort to persist

Part III, propositions 6 and 7 introduce the effort, often called conatus, through which each thing strives to persevere in its being. Spinoza identifies this striving with the thing's actual essence. Applied to human beings, the account makes desire part of what we are, rather than an intrusion into an otherwise detached intellect.

In the scholium to proposition 9, he connects desire with appetite together with consciousness of appetite. He also reverses a familiar explanation of valuation: we do not first judge something good and therefore strive for it; we call it good because we strive for it. This is part of his account of desire and judgment. It should not be mistaken for a recommendation to endorse every desire we happen to have.

The ethical argument has to distinguish desires that help us act through understanding from those through which we remain vulnerable to external determination. Part IV, proposition 24 connects acting through virtue with acting through reason and seeking what is useful to our preservation. Proposition 35 argues that people agree in nature insofar as they live under reason. Its corollaries connect rational self-interest with the usefulness of other people and shared advantage.

This matters because "persevering in one's being" can otherwise sound like permission for isolated selfishness. Spinoza's reasoning does not stop with the survival of a solitary individual. He argues that rationally guided people can support one another. Whether a particular act benefits someone still requires an argument about what it does; calling it self-interest cannot settle that question on its own.