PETTY, WILLIAM

(1623–1687)

Sir William Petty was born in London in very modest circumstances, the son of a clothmaker. After some years in the navy of King Charles I, he studied medicine in the Netherlands; in Paris, where he became a friend of the philosopher Thomas Hobbes; and at Oxford. In 1650, at the age of twenty-seven, he became professor of anatomy at Oxford, resigning the next year when he was appointed physician-general to Cromwell's army in Ireland.

Much of the rest of Petty's life was spent in Ireland in various capacities. He organized a major topographical survey that was needed for the redistribution of the forfeited property of Catholic landowners; after the restoration of Charles II he was a member of parliament for Ireland and was engaged in managing an industrial colony on the estate he had acquired in County Kerry. In his London life he was one of the group of philosophers and scientists, including Robert Boyle and John Graunt (1620–1674), who founded the Royal Society. He was knighted in 1661.

Petty's major intellectual contributions to both economics and demography fall under the broad rubric of political arithmetic, a term he invented. This was the application of Francis Bacon's (1561–1626) methods of natural philosophy to understanding social conditions and economic life–on the assumption that the body politik could be studied quantitatively in the same manner as the body natural. In his account of Petty in Brief Lives (c. 1690), John Aubrey concisely, if somewhat dismissively, characterized the approach as "reducing polity to numbers." Petty's work laid the foundations for the development of systematic social and economic statistics by subsequent scholars such as Charles Davenant (1656–1714) and Gregory King (1648–1712). On the basis of his pamphlet Verbum Sapienti (1690, a posthumous publication, like most of Petty's writings) Richard Stone (1997) calls Petty "the originator of national accounting." This general perspective and its influence on the thinking of his contemporaries and successors is the main reason Petty has a place in the history of demography: Population dynamics were to him an integral part of social accounting.

Petty also made specific demographic contributions, in particular in estimating mortality and population size, chiefly of major cities. He played a role, most likely minor, in the preparation of Graunt's pathbreaking Observations on the (London) bills of mortality (1662). Petty has sometimes been credited with virtual authorship of this work, but a detailed investigation by his later editor Charles Henry Hull found little evidence to support that contention. Stone agrees that such an attribution is baseless. Petty admired Graunt's work and drew on it in his own studies, especially of the Dublin bills of mortality.

His estimates of city sizes–based on calculations such as the number of burials divided by the supposed death rate or the number of houses multiplied by the average household size (guessed)–he recognized as highly conjectural, needing to be replaced by independent enumerations. (His population of London was much too large, that of Paris too small.) At the end of his Observations on the Dublin Bills (1683), he wrote: "Without the knowledge of the true number of the people, as a principle, the whole scope and use of keeping bills of birth and burials is impaired; wherefore by laborious conjectures and calculations to deduce the number of people from the births and burials, may be ingenious, but very preposterous." Petty's land survey of Ireland, the results of which were published in his Political Anatomy of Ireland (1691), was effectively Ireland's first census (1659).

BIBLIOGRAPHY

SELECTED WORKS BY WILLIAM PETTY.

Petty, William. 1686. An Essay Concerning the Multiplication of Mankind: Together with Another Essay in Political Arithmetick, Concerning the Growth of the City of London: with the Measures, Periods, Causes, and Consequences thereof, 1862. 2nd edition. London: Mark Pardoe. Excerpted in Population and Development Review 10(1984): 127–133.

——. 1690. Political Arithmetick, or, A discourse concerning the extent and value of lands, people, buildings, husbandry, manufacture, commerce,…, as the same relates to every country in general… London: Robert Clavel and Hen. Mortlock.

——. 1691. The Political Anatomy of Ireland… To which is added Verbum sapienti, or, An account of the wealth and expences of England, and the method of raising taxes in the most equal manner… London: D. Brown and W. Rogers. Facsimile edition: Shannon, Ireland: Irish University Press, 1970.

——. [1899] 1964. The Economic Writings of Sir William Petty, ed. Charles H. Hull. 2 vols. New York: A. M. Kelly.

SELECTED WORKS ABOUT WILLIAM PETTY.

Aubrey, John. 1898. Brief Lives … Set Down between the Years 1669 & 1696. Oxford: Clarendon Press.

Hull, Charles H. 1900. "Petty's Place in the History of Economic Theory." Quarterly Journal of Economics 14(4): 307–340.

Stone, Richard. 1997. Some British Empiricists in the Social Sciences 1650–1900. Cambridge, Eng.: Cambridge University Press.