Q8 is part of the collateral information a subject needs independent justification for in order to gain justification for the perceptual premise from perceptual evidence.

According to Wright there exist cornerstone propositions—or simply cornerstones—for different areas of discourse. In accordance with Wright’s characterization of it, c is a cornerstone for an area of discourse d just in case for any proposition p belonging to d, p could not be justified for any subject s if s had no independent justification for accepting c (see mostly Wright 2004).[10] Cornerstones for the area of discourse about perceivable things are for instance the logical negations of sk