a)  There is a kind of experience which one might call being hardly able to distinguish. You see, e.g., two lengths, two colours, almost exactly alike. But if I ask myself, “Does this experience consist in having a peculiar feeling?”, I should have to say that it certainly isn't characterized by any such feeling alone, that a most important part of the experience is that of letting my glance oscillate between the two objects, fixing it intently, now on the one, now on the other, perhaps saying words expressive of doubt, shaking my head, etc. etc. There is, one might say, hardly any room left for a feeling of similarity between these manifold experiences.