“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.' And if, by doing this, I have proved ipso facto the existence of external things. And if, by doing this, I have proved ipso facto the existence of external things, you will all see that I can also do it now in numbers of other ways: there is
no need to multiply examples. But did I prove just now that two human hands were then in existence? I do want to insist that I did; that the proof which I gave was a perfectly rigorous one; and that it is perhaps impossible to give a better or more rigorous proof of anything whatever.”