Ever since Moore revived the gospel of certainty, philosophers content with commonsense have tried to provide a perspicuous formulation of its merits. Neither Moore nor his ablest successors have completely fulfilled this task, and although few philosophers would take up Wittgenstein's challenge, “Just try ——in a real case ——to doubt someone else's fear or pain”, many would disagree that if one does he will “find these words becoming quite meaningless”. The psychological conviction that men have in many beliefs is philosophically trivial, but the suggestion that sceptical claims are meaningless seems simply false. The problem for advocates of commonsense is that there is no evident room between psychological indubitability and logical necessity, uninteresting ‘subjective’ certainty and unattainable ‘objective’ certainty. Only by describing linguistic stringencies intermediate between psychological and logical ones can this problem be overcome.

In Philosophical Papers Moore frequently claims to ‘know with certainty’ that many empirical propositions are true.