…the Signs of the Reality of an appearance are, 1st, its Insistency (of which Sign its Vividness is again a Sign), 2nd, its sameness to all witnesses, except for differences that are but corroborative, and 3rd, its physical reactions; and the Reality is that which these Signs go toward proving; so that we have only to ask what they do prove, and the answer to that question will be the Definition of a Percept.
What they prove as thoroughly as any Actual Fact can be proved, is that genuine Percepts represent, both in their qualities and their occasions, Facts concerning Matter as independent of themselves, the Perceptions.