II. The power of an effect is defined by the power of its cause, in so far as its essence is explained or defined by the essence of its cause.
 Baruch Spinoza, Ethics (1677). copy citation

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Author Baruch Spinoza
Source Ethics
Topic power 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

“Therefore, since the power of the mind, as I have shown above, is defined by the understanding only, we shall determine solely by the knowledge of the mind the remedies against the emotions, which I believe all have had experience of, but do not accurately observe or distinctly see, and from the same basis we shall deduce all those conclusions, which have regard to the mind's blessedness.
AXIOMS.
I. If two contrary actions be started in the same subject, a change must necessarily take place, either in both, or in one of the two, and continue until they cease to be contrary.
II. The power of an effect is defined by the power of its cause, in so far as its essence is explained or defined by the essence of its cause.
vii.). (This axiom is evident from III
PROPOSITIONS.
PROP. I. Even as thoughts and the ideas of things are arranged and associated in the mind, so are the modifications of body or the images of things precisely in the same way arranged and associated in the body.” source