For the chief part of our knowledge concerning substances is not, as in other things, barely of the relation of two ideas that may exist separately; but is of the necessary connexion and co-existence of several distinct ideas in the same subject, or of their repugnancy so to co-exist.
Izan ere, substantziei buruz daukagun ezagutzaren atal garrantzitsuena ez da, beste gauza batzuetan bezala, banan existi daitezkeen bi ideiari buruz, baizik zenbait ideia bereizik subjektu berean duten lotura eta koexistentziari buruz, edo horrela koexistitzeko duten aurkakotzari buruz.