Let us start again from the consideration of our original logical purpose. We feel ourselves bound and limited in our will by physical things, by psychical contents, by the demands of other subjects, and by norms. The purpose of all our knowledge is to develop completely all that is involved in this bondage. We want to develop in an over-individual way all the obligations for our submission which are necessarily included in the given objects and the given demands of subjects. We start of course everywhere and in every direction from the actual experience, but we expand the experience by seeking those objects and those demands to which, as necessarily following from the immediately given experience, we must also submit. And in thus developing the whole system of submissions, the interpretation of the experience itself becomes transformed: the physicist may perhaps substitute imperceptible atoms for the physical object and the psychologist may substitute sensations for the real idea, and the historian may substitute combinations of influences for the real personality, and the student of norms may substitute combinations of conflicting demands for the one complete duty; yet in every case the substitution is logically necessary and furnishes us what we call truth inasmuch as it is needed to develop the concrete system of our submissions and thus to express our confidence in the order-lines of reality. And each of these substitutions and supplementations becomes, as material of knowledge, itself a part of the world of experience. 3. _The Physical and the Mental Sciences_