אתיקה, חלק III, משפט 10

Whatsoever can destroy our body, cannot be postulated therein (III. v.). Therefore neither can the idea of such a thing occur in God, in so far as he has the idea of our body (II. ix. Coroll.); that is (II. xi., xiii.), the idea of that thing cannot be postulated as in our mind, but contrariwise, since (II. xi., xiii.) the first element, that constitutes the essence of the mind, is the idea of the human body as actually existing, it follows that the first and chief endeavour of our mind is the endeavour to affirm the existence of our body: thus, an idea, which negatives the existence of our body, is contrary to our mind, &c. Q.E.D.