Zvi Biener (University of Cincinnati)
Richard Feynman referred to universal gravitation as “the greatest generalization made by the human mind.” Not surprisingly, that generalization has been of perennial interest to philosophers of science, from William Whewell to recent authors in Philosophy of Science. Their concern has been with the status of Newtonian induction, particularly with Newton’s justification of induction in Rule 3 of his Rules of Philosophizing.
I argue that we have improperly read post-Humean worries into Newton’s Rule 3. Although the resulting analyses have been illuminating, we have departed significantly from the historical record and from Newton’s own view of induction. By comparing the 1st and 2nd editions of the Principia, I show that Rule 3 was not intended as a defense of induction, but as a direct response to Christiaan Huygens. I also offer a deflationary view of universality in Newton, one that puts universal induction on par with any other, perhaps severely limited, induction.
Starting with the rule’s genesis is important. The rule first appeared only in the Principia’s second edition (1713), where it replaced the first edition’s (1687) Hypothesis 3, an alchemically-tinged claim about the mutual transformation of all bodies. But Rule 3 doesn’t mention transformation. Rather, it focuses on the invariable qualities of matter. The tension between transmutation and invariability has caused significant interpretive problems. Some have speculated that Newton abandoned Hypothesis 3 because he came to realize it conflicted with atomism or because he adopted Locke’s primary/secondary distinction. But the genesis of Rule 3 betrays a simpler story. It shows that Newton was not concerned with tempering transmutation or promoting a Lockeanism, but with Huygens’s view of gravitation in Discours de la cause de la Pensanteur (1690). The Huygensian context explains some of the rule’s most curious features, such as the discussion of hardness and indivisibility (properties that play no role in the Principia), and Newton’s odd claim (after stressing how well-founded corporeal impenetrability is) that “the argument from phenomena will be even stronger for universal gravity than for… impenetrability.”
Most importantly, the Huygensian context sheds light on Newton’s concept of universality. This concept has also been the subject of debate, since Newton went out of his way (disingenuously, to some) to assert that gravity’s universality did not entail that it was a primary or essential property. I offer a historically sensitive analysis of Newton’s adjectival and adverbial forms of universus that shows “universality” was a more deflationary concept. Its proper home was within discussions of simple induction from instances, and it was meant to indicate nothing more than the applicability of some predicate to all members of a certain class, even a highly restricted one.
Taken together, these considerations entail that Newton didn’t see induction as a methodological problem. Rather, he used induction’s non-problematic status to broaden the range of qualities that could be employed in physical explanations according to Huygens. The analysis shows the benefit of detailed contextual studies in philosophy of science. It also bolsters the case of material theorists of induction like John Norton.
