call'd Grounds), as to foretel the cast of a Dye; to play well at Tennis, Billiards, or Bowles (without long practice,) by virtue of the most elaborate Conceptions that ever have been written De Projectilibus & Missilibus, or of the Angles of Incidence and Reflection."[1]
At many other points he returns to the idea that quantitative precision is necessary in economics as in other sciences. For example, the first chapter of the Treatise of Ireland contains "six points" which the author proposes to establish. In the second chapter we encounter, in twenty postulates, "the state of the case represented in terms of number, weight, and measure, and thereby made capable of demonstrations." And in the third chapter "the 6 first mention'd points are proved out of the 20 suppositions or assertions next before going." It must not be supposed that the pseudo-geometrical form of Petty's argument is either important or novel. On the contrary Roger Coke's Treatise wherein is Demonstrated that the Church and State of England are in Equal Danger with the Trade of it (London, 1671)—the very book against which Petty's Political Arithmetick was specifically directed—is more strictly Euclidian in form than anything that Petty wrote. But Coke's demonstrations rest, in every case, upon "comparative and superlative words," not upon quantitative determinations.
Judging from Petty's professions, we might expect his works to show the strictest of statistical methods. But, as has already been said, trustworthy numerical data of social interest were far more scanty at the time when Graunt and Petty began statistical investigation than they now are. No census of England had been taken. Since Domesday no complete survey or valuation of the lands had been made. Even the amounts of imports and exports were inaccurately known. Petty was unceasing in his demands for more precise information. With that end
- ↑ Preface to Political Arithmetick, Writings, i. 244.
