The mercantilists and the physiocrats each thought that a particular social class held the key to social progress in their respective societies. What were these classes, and what element of reasonableness (from the standpoint of economic theory) was there in their advocacy for these respective classes? In today's U.S. society, do mainstream economists believe that a particular social class is the key force for development and progress? If so, describe that class and the element of reasonableness (from the standpoint of economic theory) in this belief. (If not, provide a discussion of what does constitute the source of development and progress in modern society). Offer a critique of each of the three beliefs about the sources of progress.