How does one explain to a man how he should carry out the order, “Go this way!” (pointing with an arrow the way he should go)? Couldn't this mean going the direction which we should call the opposite of that of the arrow? Isn't every explanation of how he should follow the arrow in the position of another arrow? What would you say to this explanation: A man says, “If I point this way (pointing with his right hand) I mean you to go like this” (pointing with his left hand the same way)? This just shews you the extremes between which the uses of signs vary.