A blind man, Davft Lewni, is travelling in the land of the one-eyed, where he meets Ria Liszt. As our story begins he is trying to sell her his new invention.
RL: But it’s just a stick. And it’s not even the right colour for my outfit.
DL: It is indeed said to be a stick, and not incorrectly; just a stick and yet I may, nonetheless, use it to find out how far things are from me (this actual self that is here) by assuming that it is the same stick each time I use it, and via calculations whose details we may naturally presume must exist. But to begin with, it seems reasonable to suppose that there is space and time out here (for all sorts of reasons that I presume you know of). Now, I don’t know about you, but I find that things distant in space or time are never much of a problem. And with this stick I can calculate whether there is anything of any importance in any spatial direction from here.
RL: Good for you, you big Lewni.
DL: Thank you, but I am not so great (not compared with Hume). But to return to the job in hand, I'm sure that you too could use such a device, from where you are (it being reasonable for me to suppose not only that such a place exists, but that you do too, of course (at least while I'm speaking to you))... As for your earlier objection, about the wrongness of my stick’s colouration, I must confess that I find your supposition of colouration quite nonsensical. You can hardly show me a colour (as you must admit) and so I cannot take them seriously, as scientific possibilities, until you explain how such a reification of a such fuzzily delineated class of sensations could possibly exist. Please do not insult my intelligence by asking me to believe in colours without giving me a complete (and completely logical) theory of them.
RL: But I am sure that, since I do have one good eye, I shall not really need to mess about with your stick, which is actually rather cumbersome and complicated, for a stick.
DL: Ah, but it is just such presumption that would lead you into danger, in infinitely many possible worlds, were you without the assistance of such a device as this, my stick, which you might call 'white' if you wish, as it has in itself, I'm sure, no colour. You presume that your eye can be used to see with, but if so then you might indeed see colours, which is not only absurd, prima facie, but unnecessary, e.g. I do not feel the need to see colours. [Etc. ad nauseum]