The extent to which medieval trade was based on credit does not figure among the favourite problems of economic history. Not that it has been entirely neglected, since the economic theorists have been busy over it for more than seventy-five years: it is the historian who is guilty of neglect. In his absence the field has been entirely appropriated by the economic theorist; and the latter, unsupported and unrestrained by research, inevitably produced notions unrelated to historical facts. These notions spring from the source whence have originated so many current preconceptions about the economic nature of medieval civilisation – namely, speculations as to the ‘stages’ of economic development. In the nineteenth century sociologists and economists regarded their age as biologists regard the homo sapiens, as the culmination of an evolutionary process. To them epochs of history were successive stages in the uninterrupted ascent of mankind from the crude primitivity of prehistory to the complex perfection of their own age. In accordance with this view, the economists have constructed a number of hypothetical models of the evolutionary ladder, in which every step differed from the one which followed in that it did not contain one or other element of the modern economic system, or else contained it in a less developed and a more imperfect form. As credit, especially in its alliance with trade, in fact constitutes an essential principle of our present economic system it was inevitably drawn into the schemes of economic progress. The argument was simple.