《伦理学》，第II部分，定义2
I consider as belonging to the essence of a thing that, which being given, the thing is necessarily given also, and, which being removed, the thing is necessarily removed also; in other words, that without which the thing, and which itself without the thing, can neither be nor be conceived.
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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