Note.—This pain, in so far as it has reference to the absence of the object of love, is called Regret.

Prop. XXXVII. Desire arising through pain or pleasure, hatred or love, is greater in proportion as the emotion is greater.

Proof.—Pain diminishes or constrains a man's power of activity (III. xi. note), in other words (III. vii.), diminishes or constrains the effort, wherewith he endeavours to persist in his own being ; therefore (III. v.) it is contrary to the said endeavour : thus all the endeavours of a man affected by pain are directed to removing that pain. But (by the definition of pain), in proportion as the pain is greater, so also is it necessarily opposed to a greater part of man's power of activity ; therefore the greater the pain, the greater the power of activity employed to remove it ; that is, the greater will be the desire or appetite in endeavouring to remove it. Again, since pleasure (III. xi. note) increases or aids a man's power of activity, it may easily be shown in like manner, that a man affected by pleasure has no desire further than to preserve it, and his desire will be in proportion to the magnitude of the pleasure.

Lastly, since hatred and love are themselves emotions of pain and pleasure, it follows in like manner that the endeavour, appetite, or desire, which arises through hatred or love, will be greater in proportion to the hatred or love. Q.E.D.

Prop. XXXVIII. If a man has begun to hate an object of his love, so that love is thoroughly destroyed, he will, causes being equal, regard it with more hatred than if he had never loved it, and his hatred will be in proportion to the strength of his former love.

Proof.—If a man begins to hate that which he had loved, more of his appetites are put under restraint than if he had never loved it. For love is a pleasure (III. xiii. note) which a man endeavours as far as he can to render permanent (III. xxviii.) ; he does so by regarding the object of his love as present, and by affecting it as far as he can pleasurably ; this endeavour is greater in proportion as the love is greater, and so also is the endeavour to bring about that the beloved should return his affection (III. xxxiii.). Now these endeavours are constrained by hatred towards the object of love (III. xiii. Coroll. and III. xxiii.) ; wherefore the lover (III. xi. note) will for this cause also be affected with pain, the more so in proportion as his love has been greater ; that is, in addition to the pain caused by hatred, there is a pain caused by the fact that he has loved the object ; wherefore the lover will regard the beloved with greater pain, or in other words, will hate it more than if he had never loved it, and with the more intensity in proportion as his former love was greater. Q.E.D.

Prop. XXXIX. He who hates anyone will endeavour to do him an injury, unless he fears that a greater injury will thereby accrue to himself ; on the other hand, he who loves anyone will, by the same law, seek to benefit him.