And, if I don't, then it seems really possible that this presented object really is identical with this part of the surface of this inkstand; since, when I judge, as in the cases supposed, that the surface in question is not so far as I can tell, perceptibly different from what it was, I might really be judging of the two sense data that they also were not, so far as I can tell, perceptibly different, the only difference between the two that is perceptible, being that the one seems to be of a certain size, shape or colour, and the other to be of a different and incompatible size, shape or colour.