And the phrase, “He sees what all these shades have in common,” may refer to all sorts of different phenomena, i.e., all sorts of phenomena are used as criteria for “his seeing that … ” Or all that happens may be that on being asked to bring another shade of blue he carries out our order satisfactorily. Or a patch of pure blue may appear before his mind's eye when we shew him the different samples of blue: or he may instinctively turn his head towards some other shade of blue which we haven't shewn him for sample, etc. etc.