The author of the earliest general treatise on economics, writing in the middle of the eighteenth century, regarded the entrepreneur as a key factor in production. Later economists have in general had the same feeling, though they have not defined the word entrepreneur in precisely the same manner. By some the entrepreneur has been considered to be primarily a risk or uncertainty bearer, by others an innovator, by still others a superintendent or manager. The list could easily be expanded. The tendency for economists to emphasize now one and now another aspect of entrepreneurship derives, I believe, from several factors: the variations in the volume and nature of economic opportunities, the increasing size of the business unit, and the changes in the legal forms of business organization.