Desire is man’s very essence, insofar as it is conceived to be determined, from any given affection of it, to do something.

Exp.: We said above, in P9 S, that Desire is appetite together with the consciousness of it. And appetite is the very essence of man, insofar as it is determined to do what promotes his preservation.

But in the same scholium I also warned that I really recognize no difference between human appetite and Desire. For whether a man is conscious of his appetite or not, the appetite still remains one and the same. And so—not to seem to commit a tautology—I did not wish to explain Desire by appetite, but was anxious to so define it that I would comprehend together all the strivings of human nature that we signify by the name of appetite, will, desire, or impulse. For I could have said that Desire is man’s very essence, insofar as it is conceived to be determined to do something. But from this definition (by IIP23) it would not follow that the Mind could be conscious of its Desire, or appetite. Therefore, in order to involve the cause of this consciousness, it was necessary (by the same proposition) to add: insofar as it is conceived, from some given affection of it, to be determined etc. For by an affection of the human essence we understand any constitution of that essence, whether it is innate {NS: or has come from outside}, whether it is conceived through the attribute of Thought alone, or through the attribute of Extension alone, or is referred to both at once.

Here, therefore, by the word Desire I understand any of a man’s strivings, impulses, appetites, and volitions, which vary as the man’s constitution varies, and which are not infrequently so opposed to one another that the man is pulled in different directions and knows not where to turn.