Born 1623

William Petty founded political arithmetic, the discipline of analyzing economic phenomena through number, weight, and measure rather than rhetoric. Marx called him the de facto founder of political economy.

Born 1623 in Romsey, Hampshire, a clothier's son. Went to sea at fourteen, reached France, studied at a Jesuit school, then gained Thomas Hobbes's acquaintance in Paris. Studied anatomy at Leiden and Oxford, becoming Oxford's anatomy professor in 1651.

In 1652 Cromwell appointed him to direct the Down Survey, mapping confiscated Irish Catholic lands for redistribution to soldiers. Petty devised efficient methods completing it ahead of schedule, acquiring vast Kerry estates himself. He retained influence after the Restoration, receiving a knighthood in 1661.

His central legacy is political arithmetic's methodology. In Political Arithmetick (written c.1676, published 1690), he declared his intent to express himself in terms of number, weight, or measure rather than comparative words. This earliest systematic declaration of quantitative social science directly prefigured statistics, econometrics, and national income accounting.

In A Treatise of Taxes and Contributions (1662), he analyzed rent and labor as value sources, presenting a labor theory precursor. His dictum that land is wealth's mother and labor its father became foundational for classical economics. He also attempted England's national income estimation, pioneering GDP methodology.

A Royal Society charter member who pursued catamaran designs, he died 1687 in London aged sixty-four. His contribution lies in methodological revolution: turning economics from speculation toward quantitative evidence.