Selection from – Ethics – Part IV. Of Human Bondage, or the Strength of the Emotions (Page 6)
Spinoza's Words: (pleasure is better than pain)
Proposition XVIII. Desire arising from pleasure is, other conditions being equal, stronger than desire arising from pain.
Proof.—Desire is the essence of a man, that is, the endeavour whereby a man endeavours to persist in his own being. Wherefore desire arising from pleasure is, by the fact of pleasure being felt, increased or helped; on the contrary, desire arising from pain is, by the fact of pain being felt, diminished or hindered; hence the force of desire arising from pleasure must be defined by human power together with the power of an external cause, whereas desire arising from pain must be defined by human power only. Thus the former is the stronger of the two. Q.E.D.
Comment:
Spinoza takes nothing for granted. He feels he must, in the attempt to keep his philosophy logically consistent, prove even the obvious. Thus in this proposition he shows that humans prefer pleasure over pain. But he is on his way to state the essence of his revolutionary ethical system.