William Petty, the Multiplication of Mankind, and Demographic Discourse in Seventeenth-Century England

Abstract

In the 1650s, after a century of increase, the population of England stopped growing. It was not to increase substantially again before 1750. Over the same interval, and not wholly coincidentally, scholars and theologians were trying to defend the orthodox account of how global population had increased since the Creation and must continue to do so, and the first political arithmeticians were trying to measure and analyse demographic change. This article seeks to throw fresh light on this many-sided discourse by examining William Petty's attempt to write an account of the multiplication of mankind, and the reasons why he failed to complete it. It focuses particularly on Petty's part in developing methods of measuring population density which highlighted the potential for future growth, and on the equally important demonstration by John Graunt that high and rising mortality in cities was hindering population growth in reality. As Petty's cousin Robert Southwell pointed out, Graunt's ‘rule of mortality’ was wholly incompatible with any coherent account of the future multiplication of mankind. At the end of this particular discourse, newly discovered facts about demography triumphed over the presuppositions of divinity.

John Graunt F.R.S. (1620-74): The founding father of human demography, epidemiology and vital statistics

“…10 Once again he may have overestimated the true figure, perhaps by about twenty to thirty per cent. 25,26 Despite these relatively minor inaccuracies his population estimates represented the first rational attempt to calculate a population size as distinct from one derived from a survey or census. They also provided denominators for his epidemiological results.…”

“…20 It was for this reason that Graunt was interested not only in the total population but also in population density and therefore, by implication, what size of population a country could sustain. 26 Graunt's estimate of the number of men able to bear arms, and therefore to be eligible for military service, was also made for political purposes. Graunt defined this group as those aged 16-56 and then embarked on perhaps the most tortuous of his many sequences of assumptions and extrapolations.…”

“…20 It was for this reason that Graunt was interested not only in the total population but also in population density and therefore, by implication, what size of population a country could sustain. 26 …”