De Gravitatione reconsidered: The changing significance of experimental evidence for Newton's metaphysics of space

Abstract

I argue that Isaac Newton's De Gravitatione should not be considered an authoritative expression of his thought about the metaphysics of space and its relation to physical inquiry. I establish the following narrative: In De Gravitatione (circa 1668-84), Newton claimed he had direct experimental evidence for the work's central thesis: that space had "its own manner of existing" as an affection or emanative effect. In the 1710s, however, through the prodding of Roger Cotes and G. W. Leibniz, he came to see that this evidence relied on assumptions that his own Principia rendered unjustifiable. Consequently, he (i) revised the conclusions he explicitly drew from the experimental evidence, (ii) rejected the idea that his spatial metaphysics was grounded in experimental evidence, and (iii) reassessed the epistemic status of key concepts in his metaphysics and natural philosophy. The narrative I explore shows not only that De Gravitatione did not constitute the metaphysical backdrop of the Principia as Newton ultimately understood it, but that it was the Principia itself that ultimately lead to the demise of key elements of De Gravitatione. I explore the implications of this narrative for Andrew Janiak's and Howards Stein's interpretations of Newton's metaphysics.