“The main Business of natural Philosophy” pp 107-177 | Cite as

# Uncovering the Methodology of the *Principia* (II): The Phase of Model Application, Theory Formation and Theory Application

## Abstract

At the start of Book III of the *Principia*, Newton noted that in Books I and II he had “presented [tradidi] principles of philosophy that are not, however, philosophical but strictly mathematical – that is, those on which the study of philosophy can be based [ex quibus videlicet in rebus philosophicis disputari possit]” and that “[i]t still remains for us to exhibit the system of the world from these same principles [ut ex iisdem principiis doceamus constitutionem systematis mundani].” In Book III, Newton’s physico-mathematical treatment of force turned into a physical account of the forces in the empirical world. Correspondingly, Newton implicitly offered a physical reinterpretation of quantity of matter in Book III, which explains why, in manuscript material prepared for the third edition, Newton set out to define “body” (“*corpus*”) as any moveable and tangible thing that offers resistance to touch and of which the resistance can be sensed if it is big enough (“Corpus voco rem omnem ↓mobilem &↓ tangibilem qua tangentibus resistitur, & cujus resistentia, si satis magna sit, sentire potest.”).

## Keywords

Centripetal Force Inductive Generalization Universal Gravitation Apsidal Motion Proposition Versus## References

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