P10: An idea that excludes the existence of our Body cannot be in our Mind, but is contrary to it.

Dem.: Whatever can destroy our Body cannot be in it (by P5), and so the idea of this thing cannot be in God/Nature insofar as he has the idea of our Body (by IIP9 C), i.e. (by IIP11 and P13), the idea of this thing cannot be in our Mind.

On the contrary, since (by IIP11 and P13) the first thing that constitutes the essence of the Mind is the idea of an actually existing Body, the first and principal {tendency} of the striving of our Mind (by P7) is to affirm the existence of our Body. And so an idea that denies the existence of our Body is contrary to our Mind, etc., q.e.d.