"[E]conomic relations constitute a machinery by which men devote their energies to the immediate accomplishment of each other's purposes in order to secure the ultimate accomplishment of their own, irrespective of what those purposes of their own may be, and therefore irrespective of the egoistic or altruistic nature of the motives which dictate them and which stimulate efforts to accomplish them. And the things and doings with which economic investigation is concerned will therefore be found to include everything which enters into the circle of exchange—that is to say, everything with which...