E4P51D
Demonstration — Part IV
Latin
Est enim favor amor erga illum qui alteri benefecit (per 19 affectuum definitionem) atque adeo ad mentem referri potest quatenus hæc agere dicitur (per propositionem 59 partis III) hoc est (per propositionem 3 partis III) quatenus intelligit ac proinde cum ratione convenit etc. Q.E.D.
English (Elwes 1883)
Approval is love towards one who has done good to another (Def. of the Emotions, xix.); therefore it may be referred to the mind, in so far as the latter is active (III. lix.), that is (III. iii.), in so far as it understands; therefore, it is in agreement with reason, &c. Q.E.D.
Another Proof.--He, who lives under the guidance of reason, desires for others the good which he seeks for himself (IV. xxxvii.); wherefore from seeing someone doing good to his fellow his own endeavour to do good is aided; in other words, he will feel pleasure (III. xi. note) accompanied by the idea of the benefactor. Therefore he approves of him. Q.E.D.