Ética, Parte IV, Proposición 43

Localized pleasure or stimulation (titillatio) is pleasure, which, in so far as it is referred to the body, consists in one or some of its parts being affected more than the rest (see its Definition, III. xi. note); the power of this emotion may be sufficient to overcome other actions of the body (IV. vi.), and may remain obstinately fixed therein, thus rendering it incapable of being affected in a variety of other ways: therefore (IV. xxxviii.) it may be bad. Again, grief, which is pain, cannot as such be good (IV. xli.). But, as its force and increase is defined by the power of an external cause compared with our own (IV. v.), we can conceive infinite degrees and modes of strength in this emotion (IV. iii.); we can, therefore, conceive it as capable of restraining stimulation, and preventing its becoming excessive, and hindering the body's capabilities; thus, to this extent, it will be good. Q.E.D.