In his 1690 preface to Political Arithmetick, William Petty explained:

Petty had been trained in medicine and was among the first generation to teach Harvey's theory of circulation at Oxford. As his preface indicates, Petty was fascinated by mathematics’ apparent capacity to give experiential, even sensual, validity to ideas that are fundamentally abstract. Convinced by Harvey's argument, Petty saw the potential of applying a new sort of reasoning to other subjects of philosophical concern, including politics, sovereignty and wealth. And even those who were less interested in mathematical reasoning appreciated the implications of Harvey's mathematically-inflected concept of circulation for the nation's financing challenges.

Described in the 1628 publication of De motu cordis and taught by Harvey as part of the natural philosophy course of study at Cambridge, the theory that the heart forces blood through the body in a cyclical-motion circulatory system suggested how money, like blood, could be recirculated, increasing wealth and production through continuous repetition rather than through an increased supply of bullion into the system.