P9: Both insofar as the Mind has clear and distinct ideas, and insofar as it has confused ideas, it strives, for an indefinite duration, to persevere in its being and it is conscious of this striving it has.

Dem.: The essence of the Mind is constituted by adequate and by inadequate ideas (as we have shown in P3). So (by P7) it strives to persevere in its being both insofar as it has inadequate ideas and insofar as it has adequate ideas; and it does this (by P8) for an indefinite duration. But since the Mind (by IIP23) is necessarily conscious of itself through ideas of the Body’s affections, the Mind (by P7) is conscious of its striving, q.e.d.

Schol.: When this striving is related only to the Mind, it is called Will; but when it is related to the Mind and Body together, it is called Appetite. This Appetite, therefore, is nothing but the very essence of man, from whose nature there necessarily follow those things that promote his preservation. And so man is determined to do those things.

Between appetite and desire there is no difference, except that desire is generally related to men insofar as they are conscious of their appetite. So desire can be defined as appetite together with consciousness of the appetite.

From all this, then, it is clear that we neither strive for, nor will, neither want, nor desire anything because we judge it to be good; on the contrary, we judge something to be good because we strive for it, will it, want it, and desire it.