《伦理学》，第IV部分，命题71
Only free men are thoroughly grateful one to another.
证明
Only free men are thoroughly useful one to another, and associated among themselves by the closest necessity of friendship (IV. xxxv., and Coroll. i.), only such men endeavour, with mutual zeal of love, to confer benefits on each other (IV. xxxvii.), and, therefore, only they are thoroughly grateful one to another. Q.E.D.
附释
The goodwill, which men who are led by blind desire have for one another, is generally a bargaining or enticement, rather than pure goodwill. Moreover, ingratitude is not an emotion. Yet it is base, inasmuch as it generally shows, that a man is affected by excessive hatred, anger, pride, avarice, &c. He who, by reason of his folly, knows not how to return benefits, is not ungrateful, much less he who is not gained over by the gifts of a courtesan to serve her lust, or by a thief to conceal his thefts, or by any similar persons. Contrariwise, such an one shows a constant mind, inasmuch as he cannot by any gifts be corrupted, to his own or the general hurt.
Benedict de Spinoza, The Ethics (Ethica Ordine Geometrico Demonstrata), 由R. H. M. Elwes译自拉丁文.
首次出版于The Chief Works of Benedict de Spinoza，第II卷（London：George Bell and Sons，1884）。
本译文在美国已超出版权保护期（1884年出版于美国），在版权期限为作者终身加100年或更短的任何地方同样如此；其译者卒于1892年。
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