Dialogue about G. E. Moore's famous proof, using the following passages from his article, "Proof of an External World":

"proof of the existence of things outside of us... I can now give a large number of different proofs [of the existence of things outside of us], each of which is a perfectly rigorous proof... I can prove now, for instance, that two human hands exist. How? By holding up my two hands, and saying, as I make a certain gesture with the right hand, "Here is one hand", and adding, as I make a certain gesture with the left, "and here is another"

"the proof which I gave was a perfectly rigorous one; and... it is perhaps impossible to give a better or more rigorous proof of anything whatever.... (1)... the premiss which I adduced as proof of the conclusion was different from the conclusion I adduced it to prove; (2)... the premiss which I adduced was something which I knew to be the case, and not merely something which I believed but which was by no means certain, or something which, though in fact true, I did not know to be so; and (3)... the conclusion did really follow from the premiss."