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.
II. Pleasure is the transition of a man from a less to a greater perfection.
III. Pain is the transition of a man from a greater to a less perfection.
Explanation—I say transition: for pleasure is not perfection itself. For, if man were born with the perfection to which he passes, he would possess the same, without the emotion of pleasure. This appears more clearly from the consideration of the contrary emotion, pain. No one can deny, that pain consists in the transition to a less perfection, and not in the less perfection itself: for a man cannot be pained, in so far as he partakes of perfection of any degree. Neither can we say, that pain consists in the absence of a greater perfection. For absence is nothing, whereas the emotion of pain is an activity; wherefore this activity can only be the activity of transition from a greater to a less perfection—in other words, it is an activity whereby a man's power of action is lessened or