The knowledge of good and evil is nothing else but the emotions of pleasure or pain, in so far as we are conscious thereof.
 Baruch Spinoza, Ethics (1677). copy citation

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Author Baruch Spinoza
Source Ethics
Topic pain evil
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

“For the emotion which we undergo can only be checked or destroyed by an emotion contrary to, and stronger than, itself, in other words, (by the general Definition of the Emotions) only by an idea of a modification of the body contrary to, and stronger than, the modification which we undergo. PROP. VIII. The knowledge of good and evil is nothing else but the emotions of pleasure or pain, in so far as we are conscious thereof. Proof.—We call a thing good or evil, when it is of service or the reverse in preserving our being (IV. Deff. i. and ii.) , that is (III. vii.) , when it increases or diminishes, helps or hinders, our power of activity.” source