On the Origin and Nature of the Emotions Propositions 37, 38, 43 &44

37 Desire arising through pain or pleasure, hatred or love, is greater in proportion as the emotion is greater. Pain diminishes or constrains man's power of activity, in other words, diminishes or constrains the effort, wherewith he endeavours to persist in his own being; therefore 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 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. 38 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. 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 which a man endeavours as far as he can to render permanent; 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. Now these endeavours are constrained by hatred towards the object of love; wherefore the lover 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. 43 Hatred is increased by being reciprocated, and can on the other hand be destroyed by love. He who conceives, that an object of his hate hates him in return, will thereupon feel a new hatred, while the former hatred (by hypothesis) still remains (E3P40). But if, on the other hand, he conceives that the object of hate loves him, he will to this extent (E3P30) regard himself with pleasure, and (E3P29) will endeavour to please the cause of his emotion. In other words, he will endeavour not to hate him (E3P41), and not to affect him painfully; this endeavour (E3P37) will be greater or less in proportion to the emotion from which it arises. Therefore, if it be greater than that which arises from hatred, and through which the man endeavours to affect painfully the thing which he hates [by E3P26], it will get the better of it and banish the hatred from his mind. Q.E.D. 44 Hatred which is completely vanquished by love passes into love: and love is thereupon greater than if hatred had not preceded it. The proof proceeds in the same way as E3P38: for he who begins to love a thing, which he was wont to hate or regard with pain, from the very fact of loving feels pleasure. To this pleasure involved in love [see its definition in E3P13CN] is added the pleasure arising from aid given to the endeavour to remove the pain involved in hatred (E3P37), accompanied by the idea of the former object of hatred as cause.