Since agricultural history first acquired independent status it has been carried forward without much theoretical direction. So much research has been done in the field, however, that possibly a tentative general theory for further work may now be advanced. To be useful, an historical hypothesis should probably center on some common denominator of human experience. One possible common denominator is that all men are located within, or are a certain definite distance from metropolitan unit. All those who live within a certain given zone around the metropolis have at least one common experience: they are all some specific distance from the metropolis. Furthermore, for any given group of people this one common experience may have shaped many of their ideas and actions. Since human events take place in time and space, a theory based primarily on these dimensions might be at least roughly applicable to most history.