Eric Schliesser

In this paper I clarify what Newton could have meant when he insisted that gravity is a real force. I interpret Newton’s speculative treatment of gravity as a relational, accidental quality of matter that arises through what Newton calls “the shared action” of two bodies. I argue that when Newton drafted the first edition of the Principia in the mid 1680s, he thought that (at least a part of) the cause of gravity is the disposition inherent in any individual body, but that the force of gravity is the actualization of that disposition; a necessary condition for the actualization of the disposition is the actual obtaining of a relation between two bodies having the disposition. The cause of gravity is not essential to matter because God could have created matter without that disposition. Nevertheless, at least a part of the cause of gravity inheres in individual bodies and were there one body in the universe it would inhere in that body. On the other hand, the force of gravity is neither essential to matter nor inherent in matter, because (to repeat) it is the actualization of a shared disposition. A lone part-less particle would, thus, not generate a gravity field.

This paper is a critical response to Hylarie Kochiras’ “Gravity and Newton’s substance counting problem,” Studies in History and Philosophy of Science 40 267–280. First, the paper argues that Kochiras conflates substances and beings; it proceeds to show that Newton is a substance monist. The paper argues that on methodological grounds Newton has adequate resources to respond to the metaphysical problems diagnosed by Kochiras. Second, the paper argues against the claim that Newton is committed to two speculative doctrines attributed to him by Kochiras and earlier Andrew Janiak: i) the passivity of matter and ii) the principle of local causation. Third, the paper argues that while Kochiras’ arguments about Newton’s metaphysical commitments are mistaken, it qualifies the characterization of Newton as an extreme empiricist as defended by Howard Stein and Rob DiSalle. In particular, the paper shows that Newton’s empiricism was an intellectual and developmental achievement that built on non trivial speculative commitments about the nature of matter and space.Keywords: Newton; Substance; Action at a distance; Space; Matter; Empiricism

The main aim of this paper is to explore why it is so important for Hume to defi ne ‘cause’ as he does. This will shed light on the signifi cance of the natural/philosophical relation (hereafter NPR) distinction in the Treatise. Hume's use of the NPR distinction allows him to dismiss on general grounds conceptions of causation at odds with his own. In particular, it allows him to avoid having to engage in detailed re-interpretation of potentially confl icting theories formulated by natural philosophers. Moreover, it provides an instance of the normative nature of Hume's “science of man.” The paper argues that the NPR distinction - in conjunction with the so-called copy principle - is meant to undercut appeals to the authority of theories not founded on Hume's “principles.” In order to illustrate its claims about Hume, this essay explores some aspects of Newton's natural philosophy. Finally, this paper resolves a long-standing interpretive problem: how to reconcile Hume's two “defi nitions” of causation in the Treatise

David Hume's philosophy, especially the positive project of his science of man, is often thought to be modeled on Newton's successes in natural philosophy. Hume's self-described experimental method (see the subtitle to Treatise) and the resemblance of his rules of reasoning (Treatise, 1.3.15)1 with Newton's are said to be evidence for this position (Noxon 1973; De Pierris 2002). Hume encourages this view of his project by employing Newtonian metaphors: he talks of an attraction in the mental world on a par with that in the natural world (1.1.4.6). Hume infers the existence of habits as a kind of mental force (EHU 5.2.2) analogous to gravity; the discovery of the the principles of association, which in thehe calls his most important achievement see the section on Association in the entry on Hume in this Encyclopedia, are, then, analogous to the laws of motion. Hume certainly appears to want his readers to feel that he is modeling his project on the successes of natural philosophy, exemplified by Newton. In the Introduction to the Treatise and even more explicitly in the opening pages of EHU (1.15), Hume suggests that his science of man can parallel recent achievements in natural philosophy (with rather obvious nods to Newton's successes in planetary astronomy). And at the start of EPM, he echoes Newton's rejection of hypotheses (1.10). There is, thus, no doubt that Hume wants his readers to believe that Newton forms a kind of model