- Harper and Ducheyne on Newton

*Isaac Newton’s Scientific Method, Turning Data into Evidence about Gravity & Cosmology*, Oxford University Press, 2011

*The Main Business of Natural Philosophy, Isaac Newton’s Natural-Philosophical Methodology*, Springer, 2102

The years 2011–12 will be regarded as memorable ones for the “Newtonian industry” since they have witnessed the publication of two beautiful and long awaited books devoted to Newton’s method and philosophy. They deserve great attention and praise, and I warmly recommend them to any reader interested in 17th and 18th century science and philosophy. The favorable conjunction of 2011–12 should not come as a surprise for those who have been following the recent trends in Newtonian scholarship. Indeed, after the great generation of H. W. Turnbull, A. Koyré, I. B. Cohen, D. T. Whiteside, B. J. T. Dobbs, A. R. Hall, Mary Boas Hall, and R. S. Wesftall, Isaac Newton has continued to be the object of intense historical research. In the 1990s, a new wave of historians of mathematics, who capitalized on the immense riches of Whiteside’s edition of the *Mathematical Papers* (1967–1981), produced a flood of essays devoted to rather technical aspects of Newton’s oeuvre. An incomplete list includes Michel Blay, Dana Densmore, Herman Erlichson, Bruce Brackenridge, François De Gandt, Bruce Pourciau, and Michael Nauenberg.^{1} Now the pendulum seems to be swinging towards philosophy, rather than mathematics, as is immediately apparent from the titles of the two books under review. The focus of Harper and Ducheyne’s books is Newton as the originator of a new method—an alternative and more effective method than the hypothetico-deductive one. **[End Page 463]**

In what follows I will not have the space to delve into all the details of the books under review: such a task would require one to exceed even the generous word limit granted by *Perspectives on Science.* What I will try to do is to provide the reader with an account of the main theses defended in these books by framing them within the context of their respective interpretative traditions. In the closing paragraphs I will attempt to suggest new historiographical approaches that might complement what has been achieved by Harper and Ducheyne.

Harper’s aim in *Isaac Newton on Scientific Method* is to provide a systematic and comprehensive treatment of Newton’s argument in support of the idea of universal gravitation, based on a combination of accurate experimental and observational results^{2}, mathematical inferences^{3} and epistemological assumptions^{4}. Newton’s starting point is the notion that the familiar force of gravity that acts close to the Earth’s surface is, in fact, a long-range force responsible for the motion of primary, secondary planets, and comets, the ebb and flow of tides, as well as for the shape of planets. Part of the problem with Newton’s argument is that in order to capture its cogency one has to read the *Principia* from cover to cover. Indeed, in the *Principia* there is no *single* argument, but a complex handling of mathematical models which are confronted with experimental data. The mathematical sophistication of Newton’s work and his stringent demand for accuracy were unprecedented in his times. As Harper shows, there was something new in Newton’s way of handling models and measuring theoretical parameters. Previous natural philosophers, such as Galileo and Huygens, had followed what might be called a hypothetico-deductive method, whereby a hypothesis is tested by comparing predictions drawn from it with experimental data. If the predictions are accurate enough, the hypotheses can be considered corroborated, whereas small deviations between prediction and observation can be attributed to disturbing factors. As I. B. Cohen, and later George Smith, have demonstrated in great detail, Newton proceeded differently (Cohen 1980 and Smith 2002). Harper puts it as follows: “Newton’s treatment of these deviations exemplifies a method of successive approximations [. . .]. On this method, deviations from the model developed so far count as new *theory-mediated* phenomena to be exploited as carrying information to aid in developing a more accurate successor” (p. 6). Typically, the deviations from Keplerian motions exhibited by planets are interpreted...