Now as a matter of fact there are no two concrete things in the world in which there cannot be found some sameness. Both somehow affect sentiency; we say they consist of matter. Both can be measured in size, breadth, and height: we say, they are extended. Both are at any given moment in a certain relation to other things: we say, they are in space. Both have a definite form and consist of one or several special structures (i. e., so to say, inside-forms). All things can in some way or other be classed together under one heading. These samenesses of things go along with differences, and the degree of sameness in the different things varies greatly. Whether there is any sameness and difference at all in the world, cannot be decided _a priori_, but is a problem which can be solved only on the ground of, first, an _a posteriori_ statement of the facts, second, a systematical arrangement of the facts. If this is accomplished we can venture into a methodical investigation as to the nature of the samenesses as well as the differences that obtain in the universe, and having arranged them in a system, we can apply _a priori_ this system to facts with which we are not as yet acquainted. The many samenesses which are experienced are not purely mental additions; they are not mere subjective imputations transferred upon objective existence. They are real; i. e. there are in the objective things actual features which allow of certain substitutions. A ray of light awakens in some feeling substance the traces left by former rays of light; and this reawakening is called memory. The perception of sameness is the beginning of mind, and it involves the perception of difference as a natural consequence. Suppose that the stuff of which the world consists were capable of acquiring feeling, but there were no samenesses whatever; which would mean that every smallest piece of the world-stuff were a particular thing by itself and in every respect unlike every other piece, of a different material or of no material at all, of different size or of no size at all, and also possessed of a different number of space dimensions. In such a world all the impacts made upon a sentient being would be different; not one would be like the other, and all feelings would present a chaos without uniformities, worse than the most complex crazy-quilt. Under such circumstances mind would be impossible: it would neither originate nor could it develop.