  This last point shows that Moore's defence of common sense is not as much of a constraint on philosophical theory as one might at first have thought; for philosophical analysis can reveal to us facts about the ‘principal or ultimate subject’ of a truistic proposition which are by no means what common sense supposes. This implication is important when one turns to consider Moore's most famous paper, his ‘Proof of an External World’ — the text of a British Academy lecture delivered in 1939 just when Moore was retiring from his Cambridge Professorship. Moore here sets himself the task of doing what Kant had earlier set himself to do, namely providing a proof of the existence of ‘external objects’. Much of the lecture is devoted to working out what counts as an ‘external object’, and Moore claims that these are things whose existence is not dependent upon our experience. So, he argues, if he can prove the existence of any such things, then he will have proved the existence of an ‘External World’. Moore then maintains that he can do this —