P26: A thing which has been determined to produce an effect has necessarily been determined in this way by God/Nature; and one which has not been determined by God/Nature cannot determine itself to produce an effect.

Dem.: That through which things are said to be determined to produce an effect must be something positive (as is known through itself). And so, God/Nature, from the necessity of his nature, is the efficient cause both of its essence and of its existence (by P25 & P16); this was the first thing. And from it the second thing asserted also follows very clearly. For if a thing which has not been determined by God/Nature could determine itself, the first part of this {proposition} would be false, which is absurd, as we have shown.