By the second half of the thirteenth century, the social conception of a world connected by commerce and held together by a monetarily measured and regulated “flux and reflux of services” was being articulated in the Ethics commentaries of Albertus Magnus and Thomas Aquinas. As the social process of monetization gathered speed, scholastic thinkers expanded Aristotle's geometric model of exchange from its base in personal relationships to a supra-personal system of relations in which aggregate needs and decisions determined value. The great claims Aristotle made for the success of money as a measuring and commensurating medium were expanded as well. In the writings of the most sophisticated economic thinkers of the fourteenth century, the use of money as an instrument of equalization was understood to permit exchangers of unequal social status and occupation, at crossed purposes (each wanting to buy cheap and sell dear), with unequal needs, exchanging unequal goods of unequal value, to arrive, nevertheless, at an approximate equality in their economic transactions – an equality, moreover, sufficient to be named “just.” The monetized marketplace was seen to bind all producers and consumers into a geometrically conceived, self-equalizing system, regulated through a shifting market price determined by common need and estimation.

In order to show that the experience and comprehension of this social context influenced the development of scientific thought, I have been following six clusters of insights, organized into category headings, that in my view characterize the most innovative aspects of both economic thought and natural philosophy in the fourteenth century.