We are obliged in every hour of our lives to act upon beliefs which have been arrived at by inferences of these two kinds; inferences based on the assumption of uniformity in nature, and inferences which add to this the assumption of feelings which are not our own. By organizing the 'common sense' which embodies the first class of inferences, we build up the physical sciences; that is to say, all those sciences which deal with the physical, material, or phenomenal universe, whether animate or inanimate. And so by organizing the common sense which embodies the second class of inferences, we build up various sciences of mind. The description and classification of feelings, the facts of their association with each other, and of their simultaneity with phenomena of nerve-action,--all this belongs to psychology, which may be historical and comparative. The doctrine of certain special classes of feelings is organized into the special sciences of those feelings; thus the facts about the feelings which we are now considering, about the feelings of moral approbation and reprobation, are organized into the science of ethics and the facts about the feeling of beauty or ugliness are organized into the science of æsthetics, or, as it is sometimes called, the philosophy of art. For all of these the uniformity of nature has to be assumed as a basis of inference; but over and above that it is necessary to assume that other men are conscious in the same way that I am. Now in these sciences of mind, just as in the physical sciences, the uniformity which is assumed in the inferred mental facts is a growing thing which becomes more definite as we go on, and each successive generation of observers knows better what to observe and what sort of inferences may be drawn from observed things. But, moreover, it is as true of the mental sciences as of the physical ones that the uniformity is in the present stage of science an atomic uniformity. We have learned to regard our consciousness as made up of elements practically alike, having relations of succession in time and of contiguity at each instant, which relations are in all cases practically the same. The element of consciousness is the transference of an impression into the beginning of action. Our mental life is a structure made out of such elements, just as the working of our nervous system is made out of sensori-motor processes. And accordingly the interaction of the two branches of science leads us to regard the mental facts as the realities or things-in-themselves, of which the material phenomena are mere pictures or symbols. The final result seems to be that atomism is carried beyond phenomena into the realities which phenomena represent; and that the observed uniformities of nature, in so far as they can be expressed in the language of atomism, are actual uniformities of things in themselves.