Economic works and theories
Two men crucially influenced Petty's economic theories. The first was Thomas Hobbes, for whom Petty acted as personal secretary. According to Hobbes, theory should set out the rational requirements for "civil peace and material plenty". As Hobbes had centred on peace, Petty chose prosperity.
The influence of Francis Bacon was also profound. Bacon, and indeed Hobbes, held the conviction that mathematics and the senses must be the basis of all rational sciences. This passion for accuracy led Petty to famously declare that his form of science would only use measurable phenomena and would seek quantitative precision, rather than rely on comparatives or superlatives, yielding a new subject that he named "political arithmetic". Petty thus carved a niche for himself as the first dedicated economic scientist, amidst the merchant-pamphleteers, such as Thomas Mun or Josiah Child, and philosopher-scientists occasionally discussing economics, such as John Locke.
He was indeed writing before the true development of political economy. As such, many of his claims for precision are of imperfect quality. Nonetheless, Petty wrote three main works on economics, Treatise of Taxes and Contributions (written in 1662), Verbum Sapienti (1665) and Quantulumcunque Concerning Money (1682). These works, which received great attention in the 1690s, show his theories on major areas of what would later become economics. What follows is an analysis of his most important theories, those on fiscal contributions, national wealth, the money supply and circulation velocity, value, the interest rate, international trade and government investment.
Many of his economic writings were collected by Charles Henry Hull in 1899 in The Economic Writings of Sir William Petty.
Hull, in his scholarly article 'Petty's Place in the History of Economic Theory' (1900) proposed a division of the economic writings of Petty in three (or four) groups:
the first group, written when Petty had returned to London after finishing his "Down Survey" in Ireland, consists mainly of A Treatise of Taxes & Contributions (written and first published 1662) and Verbum Sapienti (written 1665, printed 1691). These texts relate to the discussions about fiscal issues, following the Restoration and the expenses of the first Dutch war.
the second group holds The Political Anatomy of Ireland and Political Arithmetick. These texts were written some ten years later in Ireland. As Hull writes, the "direct impulse to their writing came from Dr. Edward Chamberlayne's Present State of England, published 1669".
Again ten years later the third group of pamphlets was written, that were contributions to the dispute whether London was a larger city than Paris, and that are titled the Essays in Political Arithmetick by Hull. This group of pamphlets had a close relation to John Graunt's Observations upon the Bills of Mortality of London.
The Quantulumcunque concerning Money (written in 1682, and printed in 1695, and perhaps in 1682), can probably be considered as belonging to a group of its own.
The division given here was still used by scholars at the end of the twentieth century.
