‘Desire’, Spinoza says, ‘is the very essence of the human.’ For Spinoza, there is no ‘essence of humanity’, as in the scholastic Aristotelian ‘rational animal’, the ζῷον ƛόγον ἔχον that Heidegger describes. Rather, in Spinoza's metaphysics each individual mode of substance, and so each human being, has its own unique essence: its conatus or striving to persevere in its being. This striving should not be understood statically, as though each being strives only to remain what it was, but dynamically, in the sense that each being strives to become what it is by actively seeking to increase its powers to affect and be affected, in thought as well as in extension. This is the metaphysical basis for Spinoza's much-lauded anti-anthropocentrism. However, human beings are not entirely unremarkable for Spinoza; they are, for one thing, highly complicated as finite modes go, capable of affecting others and being affected by them in a great many ways. And the complex dynamic striving that constitutes the essence of each human being is clearly both mental as well as corporeal: I strive to increase the power of my body to act, but also my mind's power to think, in one and the same movement. Conversely, as a human being, my incapacities are both corporeal, insofar as there are things that my body cannot do, and mental, insofar as there are things that I do not and cannot adequately understand. The fact that we must have such incapacities in general is inescapable: it is one of the demonstrated propositions of Part IV of the Ethics, but it is also axiomatic. Spinozist ethics is the practice of systematically replacing such incapacities in thought and extension with active powers, so that one actively produces the effects that follow from one's nature, rather than passively undergoing changes determined by natures other than one's own.

To what extent is our striving or desire conscious? In the scholium to Proposition 9 of Part III of the Ethics, Spinoza seems to suggest that human desire is essentially conscious: ‘desire can be defined as appetite together with consciousness of the appetite’.