Spinoza's Ethics Part 1, Proposition 3

by Corry Shores

[the following is quotation; my summary and commentary is in brackets.]

Spinoza, Ethics, Part I, Proposition III:

Prop. III. Things which have nothing in common cannot be one the cause of the other. 

[If we have two utterly different things, we cannot say that one gives any account for the other, which means that we cannot say that one is the cause of the other.]

Proof.-If they have nothing in common, it follows that one cannot be apprehended by means of the other (Ax. v.), and, therefore, one cannot be the cause of the other (Ax. iv.). Q.E.D.

[By 'cause' we mean that on the account of which something comes about. If things have nothing in common, there is no relation between them, hence understanding one tells us nothing about the other. And if cause is that which accounts for something, and if one thing cannot account for another, then neither of these things can be the cause of the other.]

Spinoza. Ethics. Transl. Elwes. available online at: 

http://ebooks.adelaide.edu.au/s/spinoza/benedict/ethics/index.html