 The Copy Principle is an empirical thesis, which he emphasizes by offering “one contradictory phenomenon” as an empirical counterexample to the principle. He imagines someone who has had the same sorts of experiences of colors most of us have had, but has never experienced a certain shade of blue. Hume thinks that if he orders all the shades of blue he has experienced from the darkest to the lightest, he will see immediately that there is a gap where the missing shade should be. Then he asks