We know nothing to be certainly good or evil, save such things as really conduce to understanding, or such as are able to hinder us from understanding.
 Baruch Spinoza, Ethics (1677). copy citation

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Author Baruch Spinoza
Source Ethics
Topic evil good
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

“the first and single basis of virtue, nor shall we endeavour to understand things for the sake of any ulterior object (IV. xxv.) ; on the other hand, the mind, in so far as it reasons, will not be able to conceive any good for itself, save such things as are conducive to understanding. PROP. XXVII. We know nothing to be certainly good or evil, save such things as really conduce to understanding, or such as are able to hinder us from understanding. Proof.—The mind, in so far as it reasons, desires nothing beyond understanding, and judges nothing to be useful to itself, save such things as conduce to understanding (by the foregoing Prop.) . But the mind” source