It has been said that in the other kinds of sameness we always find the notion of similarity. When, however, we distinguish two things as two and yet recognize them as similar, we must have what I may call a mixed experience of likeness and unlikeness. In any two things compared, the degrees of likeness and unlikeness may vary, and we may fix attention upon similarities or differences. In proportion to the attention given to dissimilar elements will the two objects be clearly distinguished from each other and discriminated as two. If the purpose in hand does not require a careful attention to differences, and if what is prominent in mind is the likeness of the two objects, the sense of duality may fall into the background, and the man pass readily from one object to the other with little consciousness that he has made a change. As I now look at the two ink-stands on my desk, I clearly recognize them as two and yet as of the one kind. Here I am as distinctly aware that they are two as I am that they are in some respects the same. But in some of the kinds of sameness I have described this sense of duality falls more into the shade. When I speak of seeing the same ink-stand twice, or when I call up in memory an ink-stand once seen, I am likely, unless I take particular pains to reflect upon my mental operation, to have but a dim realization of the fact that I have two distinct things to deal with. How those who distinguish between the immediate and the mediate objects of knowledge have a tendency to forget their distinction, and to pass unconsciously from one to the other, I have dwelt upon sufficiently. Suppose, now, that from two objects which we recognize as similar and yet distinct, we abstract one by one the elements which differ. So long as there is any difference left, we still have "identity in diversity"--similarity in the ordinary sense of the term, which implies a recognition of two things as two. When, however, the last difference disappears, all sense of duality must disappear with it, for any division or distinction within what remains is inadmissible. Things which are distinguished are distinguished through some difference. A sense of duality implies a discrimination between two, and where it is impossible to discriminate duality vanishes. Similarity, as we commonly use the word, must then disappear with the disappearance of all dissimilarity between two objects. I say "between two objects" in default of a better expression, for, of course, we have at this point no longer two objects. My meaning is, however, sufficiently plain. A sense of duality implies difference, and similarity, as commonly understood, implies duality. The similarity will then take itself off with the last difference.