P14: Except God/Nature, no substance can be or be conceived.

Dem.: Since God/Nature is an absolutely infinite being, of whom no attribute which expresses an essence of substance can be denied (by D6), and he necessarily exists (by P11), if there were any substance except God/Nature, it would have to be explained through some attribute of God/Nature, and so two substances of the same attribute would exist, which (by P5) is absurd. And so except God/Nature, no substance can be or, consequently, be conceived. For if it could be conceived, it would have to be conceived as existing. But this (by the first part of this demonstration) is absurd. Therefore, except for God/Nature no substance can be or be conceived, q.e.d.

Cor. 1: From this it follows most clearly, first, that God/Nature is unique, i.e. (by D6), that in Nature there is only one substance, and that it is absolutely infinite (as we indicated in P10 S).

Cor. 2: It follows, second, that an extended thing and a thinking thing are either attributes of God/Nature, or (by A1) affections of God/Nature’s attributes.