The external circumstances which condition conduct are variable, of course, and so they will have a varying effect upon conduct; but their variation is, in effect, construed to be of such a character only as to vary the degree of strain to which the human agent is subject by contact with these external circumstances. The cultural elements involved in the theoretical scheme, elements that are of the nature of institutions, human relations governed by use and wont in whatever kind and connection, are not subject to inquiry but are taken for granted as pre-existing in a finished, typical form and as making up a normal and definitive economic situation, under which and in terms of which human intercourse is necessarily carried on. This cultural situation comprises a few large and simple articles of institutional furniture, together with their logical implications or corollaries; but it includes nothing of the consequences or effects caused by these institutional elements. The cultural elements so tacitly postulated as immutable conditions precedent to economic life are ownership and free contract, together with such other features of the scheme of natural rights as are implied in the exercise of these. These cultural products are, for the purpose of the theory, conceived to be given a priori in unmitigated force. They are part of the nature of things; so that there is no need of accounting for them or inquiring into them, as to how they have come to be such as they are, or how and why they have changed and are changing, or what effect all this may have on the relations of men who live by or under this cultural situation.