Substance & Property, System & Relation: Metaphysical Orthodoxy in Newton’s Rational Mechanics

Zvi Biener

University of Cinicinnati

Isaac Newton’s heterodoxy is a unifying theme of Newtonian scholarship. Studies of Newton’s innovative methods for handling evidence, his subjugation of natural philosophical and metaphysical questions to experiment, and his professed agnosticism about deep causal explanation mark him as a revolutionary natural philosopher. Newton was also at odds with the prevailing trends of his time in his alchemy, biblical chronology, and theological reflection. In fact, in contemporary scholarship, heterodoxy marks Newton’s modern as well as less-modern pursuits. But Newton’s heterodoxy has been increasingly overemphasized. I argue that Newton held fast to a fairly conventional, Aristotelian-inspired thesis: that the properties and laws which govern the universe and systems within it arise from the properties and laws which govern its most basic parts. This is not a trivial claim, not even in the context of the mechanical philosophy, where it ought to seem at home! Descartes, for example, held that the conservation of motion that governs the collisions of individual parts of matter derives from God’s conversation of motion for the entire universe. For Descartes, a global constraint on matter—that its motion be universally conserved—is primary; the constraint that in each interaction the quantity of matter is likewise conserved is secondary. Descartes thus denies what I call the ‘compositionally thesis’; he holds that the properties and laws of the parts derive from the properties and laws of the whole. Similarly, in the mechanical tradition (both before and after Newton), properties of systems taken as wholes were used to derive properties of the parts of those systems. Newton was aware of such instances and could have certainly rejected the compositionally thesis, but there is no indication that he did. In this matter, his orthodoxy won out. My aim is not simply to reorient the ethos of contemporary scholarship. I argue that Newton’s commitment to the compositionality thesis bears directly on his relationship with the mechanical philosophers as well as the Galilean-Huygensian mechanical tradition. Moreover, it provides an overlooked reference point in the long-lived debate regarding the nature of Newton’s gravity. To show this, I first explicate the nature of the compositionally thesis and its Aristotelian roots. I then highlight Newton’s commitment to it in a variety of texts and use those as foil for several recent works that attempt to articulate Newton’s connection to mechanism and the mixed-mathematical tradition. Lastly, I consider how the compositionally thesis affects our understanding of a simple system: one with only two simple bodies. If there are properties and laws that apply to the entire system but are irreducible — say, a brute fact about a determinate relation that holds between the two bodies — the compositionally thesis would be violated. Since Newton might have understood gravity to a relation like this, the compositionally thesis bears directly on his view of gravity. I consider how Newton’s understanding of the global structure of space might complicate the compositionally thesis.