Full Idea
It is demonstrated that impenetrability belongs to the essence of extension and not to the essence of any other thing.
Gist of Idea
Impenetrability only belongs to the essence of extension
Source
René Descartes (Two letters on mind [1649], More, Apr 1649), quoted by Robert Pasnau - Metaphysical Themes 1274-1671 15.5
Book Reference
Pasnau,Robert: 'Metaphysical Themes 1274-1671' [OUP 2011], p.318
A Reaction
I'm not sure that I understand how pure extension can be impenetrable.
Related Idea
Idea 16683 Leibniz eventually said resistance, rather than extension, was the essence of body [Leibniz, by Pasnau]