If a thing can be conceived as non—existing, its essence does not involve existence.
 Baruch Spinoza, Ethics (1677). copy citation

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Author Baruch Spinoza
Source Ethics
Topic existence essence
Date 1677
Language English
Reference
Note Translated by R. H. M. Elwes
Weblink http://www.gutenberg.org/files/3800/3800-h/3800-h.htm

Context

“Things which have nothing in common cannot be understood, the one by means of the other; the conception of one does not involve the conception of the other. VI. A true idea must correspond with its ideate or object. VII. If a thing can be conceived as non—existing, its essence does not involve existence. PROPOSITIONS. PROP. I. Substance is by nature prior to its modifications. Proof.—This is clear from Deff. iii. and v. PROP. II. Two substances, whose attributes are different, have nothing in common.” source