I have said, that in the present part I shall merely treat of human infirmity.

The power of reason over the emotions I have settled to treat separately.
PROP.XVIII.

Desire arising from pleasure is, other conditions being equal, stronger than desire arising from pain.
Proof .-- Desire is the essence of a man (Def.

of the Emotions, i.), 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.