《伦理学》，第IV部分，命题19
Every man, by the laws of his nature, necessarily desires or shrinks from that which he deems to be good or bad.
证明
The knowledge of good and evil is (IV. viii.) the emotion of pleasure or pain, in so far as we are conscious thereof; therefore, every man necessarily desires what he thinks good, and shrinks from what he thinks bad. Now this appetite is nothing else but man's nature or essence (Cf. the Definition of Appetite, III. ix. note, and Def. of the Emotions, i.). Therefore, every man, solely by the laws of his nature, desires the one, and shrinks from the other, &c. Q.E.D.
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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