4p51a.md (343B)
1 He, who lives under the guidance of reason, desires for others the good which he 2 seeks for himself (IV. xxxvii.); wherefore from seeing someone doing good to his 3 fellow his own endeavour to do good is aided; in other words, he will feel 4 pleasure (III. xi. note) accompanied by the idea of the benefactor. Therefore he 5 approves of him. Q.E.D. 6 7