William Petty

William Petty (1623-1687) published only one work during his lifetime (in 1662), but in the ten years following his death four others were printed. We term these "works" because they were more tracts than books; they lacked coherent organizational structure. Petty was a brilliant thinker who rose from poverty as a weaver's son and mastered Latin, Greek, French, arithmetic, geometry, and navigation by the time he was fifteen years old. He ended life as a wealthy man after spending time as a sailor, physician (he studied anatomy in Paris with Hobbes), inventor, surveyor, and—most important—being the first economic writer to advocate the measurement of economic variables. His economic writings were not general treatises; they were the result of his practical interests in matters such as taxation, politics, money, and measurement.
Petty's Political Arithmetic was written in 1676 but not published until 1690. He seemed conscious that he was breaking new ground by discussing the methodology of political arithmetic.

The method I take to do this is not yet very usual. For instead of using only comparative and superlative words and intellectual arguments, I have taken the course ... to express myself in terms of number, weight, or measure; to use only arguments of sense, and to consider only such causes as have visible foundations in nature.

Petty was influenced by broad philosophical movements that took place before and during his lifetime. Aristotle and the scholastics developed their arguments almost exclusively with words, but Descartes, Hobbes, and Bacon brought induction, empiricism, and mathematics to the attention of the intellectual community.

Petty apparently was the first to explicitly advocate the use of what we would call statistical techniques to measure social phenomena. He tried to measure population, national income, exports, imports, and the capital stock of a nation. His methods were crude almost beyond belief, leading Adam Smith to indicate that he had little use for political arithmetic.

A fairly typical mercantilist in his analysis and policy conclusions, Petty does represent the beginning of an aspect of economics and the social sciences whose full conclusion has yet to play out. In the appendix to Chapter 1 we examined some of the methodological issues in economics; one of the most crucial concerns was the mechanisms used in an attempt to establish fundamental principles. One of the strongest traditions in economics has been a literary methodology whereby problems are explored and theories are developed by the use of language. Until the end of the nineteenth century, testing of hypotheses was done by appealing to present circumstances or to history, and the use of statistics was minimal. Petty's seminal insight that ideas should be expressed in terms of numbers, weight, and measure and that only arguments that have visible foundations in nature should be accepted is the cornerstone of modern thinking in economics. His early use of statistics was crude, but the methodological position he represents has a lineage from the empirical inductionism of his time to the modern application of econometrics that is prevalent in contemporary economics journals. We will return to these issues of measurement and estab­lishment of the principles of economics in Part IV Economics and Its Critics.