4p18d.md (588B)
1 Desire is the essence of a man (Def. of the Emotions, 2 i.), that is, the endeavour whereby a man endeavours to persist 3 in his own being. Wherefore desire arising from pleasure is, by 4 the fact of pleasure being felt, increased or helped; on the 5 contrary, desire arising from pain is, by the fact of pain being 6 felt, diminished or hindered; hence the force of desire arising 7 from pleasure must be defined by human power together with the 8 power of an external cause, whereas desire arising from pain must 9 be defined by human power only. Thus the former is the stronger 10 of the two. Q.E.D. 11 12