HKB
will be (III. xiii.) affected with hatred towards the loved object and also towards his rival (III. xv. Cor.), which latter he will envy as enjoying the beloved object. Q.E.D.
*****Note--This hatred towards an object of love joined with envy is called "Jealousy," which accordingly is nothing else but a wavering of the disposition arising from combined love and hatred, accompanied by the idea of some rival who is envied. Further, this hatred towards the object of love will be greater, in proportion to the pleasure which the jealous man had been wont to derive from the reciprocated love of the said object; and also in proportion to the feelings he had previously entertained towards his rival. If he had hated him, he will forthwith hate the object of his love, because he conceives it is pleasurably affected by one whom he himself hates: and also because he is compelled to associate the image of his loved one with the image of him whom he hates. This condition generally comes into play in the case of love for a woman: for he who thinks, that a woman whom he loves prostitutes herself to another, will feel pain, not only because his own desire is restrained, but also because, being compelled to associate the image of her he loves with the parts of shame and the excreta of another, he therefore shrinks from her.
We must add, that a jealous man is not greeted by his beloved with the same joyful countenance as before, and this also gives him pain as a lover, as I will now show.
XXXVI. He who remembers a thing, in which he has once taken delight, desires to possess it under the same circumstances as when he first took delight therein.
Proof--Everything, which a man has seen in conjunction with the object of his love, will be to him accidentally a cause of pleasure (III. xv.); he will, therefore, desire to possess it, in conjunction with that wherein he has taken delight; in other words, he will desire to possess the object of his love under the same circumstances as when he first took delight therein. Q.E.D.
<<<<<Corollary--A lover will, therefore, feel pain if one of the aforesaid attendant circumstances be missing.
Proof--For, in so far as he finds some circumstance to be missing, he conceives something which excludes its existence. As he is assumed to be desirous for love's sake of that thing or circumstance (by the last Prop.), he will, in so far as he conceives it to be missing, feel pain (III. xix.). Q.E.D.
*****This pain, in so far as it has reference to the absence of the object of love, is called "Regret."
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.