Introduction

This chapter opens with an overview of the anti-Cartesian themes that inform the “experimental philosophy” that Newton pursues in the Principia (1687). Central to this discussion are Newton’s rejection of the Vortex Hypothesis and his critical stance toward Descartes’s use of hypotheses in the Principles of Philosophy (1644). Also considered are the different ways that Newton and Descartes explain celestial motions and characterize gravity and their competing claims about our capacity for knowing the essential features of bodies. The second section of the chapter focuses on the four Rules for the Study of Natural Philosophy, which are presented at the opening of Book 3 of the Principia. Special attention is given to Rule 3. This is Newton’s universalizing rule. It specifies the evidentiary conditions under which the experimental philosopher can infer that a quality belongs to all bodies universally. The Two-Set Reading of Rule 3 that is defended in the book is introduced as an alternative to the long-standard One-Set Reading of the Rule. The chapter concludes with the complete text of the “Rules for the Study of Natural Philosophy” as it was presented in the third edition (1726) Principia.