《伦理学》，第III部分，情感的定义1

We have said above, in the note to Prop. ix. of this part, that desire is appetite, with consciousness thereof; further, that appetite is the essence of man, in so far as it is determined to act in a way tending to promote its own persistence. But, in the same note, I also remarked that, strictly speaking, I recognize no distinction between appetite and desire. For whether a man be conscious of his appetite or not, it remains one and the same appetite. Thus, in order to avoid the appearance of tautology, I have refrained from explaining desire by appetite; but I have take care to define it in such a manner, as to comprehend, under one head, all those endeavours of human nature, which we distinguish by the terms appetite, will, desire, or impulse. I might, indeed, have said, that desire is the essence of man, in so far as it is conceived as determined to a particular activity; but from such a definition (cf. II. xxiii.) it would not follow that the mind can be conscious of its desire or appetite. Therefore, in order to imply the cause of such consciousness, it was necessary to add, in so far as it is determined by some given modification, &c. For, by a modification of man's essence, we understand every disposition of the said essence, whether such disposition be innate, or whether it be conceived solely under the attribute of thought, or solely under the attribute of extension, or whether, lastly, it be referred simultaneously to both these attributes. By the term desire, then, I here mean all man's endeavours, impulses, appetites, and volitions, which vary according to each man's disposition, and are, therefore, not seldom opposed one to another, according as a man is drawn in different directions, and knows not where to turn.