Selection from – Ethics – Part III. On the Nature and Origin of the Emotions (Page 16)

Spinoza's Words:(on turning hatred into love)

Proposition. XLIII. Hatred is increased by being reciprocated, and can on the other hand be destroyed by love.

Proof.—He who conceives, that an object of his hatred hates him in return, will thereupon feel a new hatred, while the former hatred still remains. But if, on the other hand, he conceives that the object of hate loves him, he will to this extent regard himself with pleasure, and will endeavour to please the cause of his emotion. In other words, he will endeavour not to hate him, and not to affect him painfully; this endeavour 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, it will get the better of it and banish the hatred from his mind. Q.E.D.