To ascribe to Newton what I have called robust action at a distance, is to miss out on significant features of his methodology, namely his desire in De mundi systemate to remain neutral with respect to defining “a species or mode of action, or a physical cause or reason [modum actionis causamve aut rationem physicam].”... Furthermore, there are clear indications that Newton thought that De mundi systemate contained no speculations or hypotheses on the cause of gravitational interaction. Newton wrote, for instance, that he wanted “to avoid all questions about the nature or quality of this force, which we would not understood to determine by any hypothesis” (Newton, A Treatise of the System of the World, 4;]--Steffen Ducheyne, "Newton on Action at a Distance." Journal of the History of Philosophy 52.4 (2014): 690 and note 95 (on p. 690).
In a classic paper, quoted above, Steffen Ducheyne went through then quite recent, renewed scholarly recent debate over the physical and metaphysical underpinnings of law of gravitation in the Principia. It was then, I think, agreed by all parties to the debate that in the Principia itself Newton intended [A] to be agnostic about its underlying cause. That is compatible with four other claims: (i) that Newton's early readers attributed all kinds of non-agnostic positions to Newton; (ii) that the Principia itself constraints any possible physics and metaphysics of the law of gravitation; (iii) that there is evidence of Newton's own views on the physics and metaphysics of the law of gravitation in his other writings that may either bear on (ii) or explain (iv) what Newton himself held about the physics and metaphysics of the law of gravitation, but did not print in the Principia.
In a number of papers, I have tried to contribute to debates over (i-iv). In particular, following (2002) work by Howard Stein, I claimed [and this bears on (ii)-(iii)-(iv)] that Newton's discarded original draft of the system of the world (which ended up being book 3 of the Principia), the so-called Treatise of the System of the World (published shortly after Newton died) --offers evidence for attributing to Newton the idea that, while drafting the Principia, he thought that gravity was the effect or manifestation of a two-fold disposition, a non-intrinsic relational quality of matter. And so lurking in the Principia is a kind of matter theory (something Katherine Brading, Zvi Biener and Chris Smeenk have argued on different, more (ahh) solid grounds.)
On my view A body has two dispositions: a “passive” disposition to respond to impressed forces which is codified in the second law of motion whereas an “active” disposition to produce gravitational force is treated as a distinct interaction codified in the third law of motion. And the “cause” of the action is “the conspiring nature of both” bodies. For the “conspiring” to occur, the bodies must share a “nature.” (For the full defense of these ideas see here and here.) In my argument, and again following Stein, I relied on passages like the following:
For all action is mutual, and makes the bodies mutually to approach onę to the other, and therefore must be the same in both bodies. It is true that we may conſider one body as attracting, another as attracted. But this diſtinction is more mathematical than natural. The attraction is really common of either to other, and therefore of the same kind in both.
Now, confronted by my interpretation of this passage, Ducheyne wants to argue that Newton's language is "rather loose, and without aiming at “speculatively metaphysical” conclusions." (689-690) And Ducheyne's evidence for this is the following passage he (partially) quotes in the footnote above:
But our purpoſe is only to trace out the quantity and properties of this force from the phænomena, and to apply what we diſcover in some simple cases, as principles, by which, in a mathematical way, we may estimate the effects thereof in more involved caſes. For it would be endleſs and impossible to bring every particular to direct and immediate observation.
We said, in a mathematical way, to avoid all questions about the nature or quality of this force, which we would not be understood to determine by any hypothesis; as it is a force which is directed towards some center; and as it regards more particularly a body in that center, we call it circum-solar, circum-terreſtrial, cir cum - jovial, and in like manner in respect of other central bodies. (Treatise pp. 4-5; emphasis in original)
And I certainly agree with Ducheyne that this passage seems to be a problem for my interpretation. It seems that when Newton composed the Treatise System of the World, he had the same methodological stance of the Principia, that is [A]. In context, it is clear that "this force" refers to the force that keeps planets in orbits. And Newton discusses and rejects a number of hypotheses (solid orbs; vortices, principle of impulse or attraction, etc.) which he attributes to Ancient and seventeenth century thinkers.
Now, I think Ducheyne misreads the the significance passage. But let's first assume Ducheyne gets it right. Notice that on Ducheyne's reading of the passage, Newton's mathematical way avoids discussion of the ontology and metaphysics of forces, that is, avoids speculation.
Now, if we go back to the first paragraph of the Newton passage I quoted above, in light of Ducheyne's emphasis on the mathematical way, we notice something fascinating:
For all action is mutual, and makes the bodies mutually to approach onę to the other, and therefore must be the same in both bodies. It is true that we may conſider one body as attracting, another as attracted. But this distinction is more mathematical than natural. The attraction is really common of either to other, and therefore of the same kind in both.
Newton explicitly offers a contrast here between the "mathematical" and natural way. And he treats the natural way as what "really" is. So, here Newton explicitly violates the injunction Ducheyne attributes to Newton. And Newton does so in terminology that evokes the passage Ducheyne offers as evidence against this happening.
One way to handle this is to claim that Newton is contradicting himself in the Treatise. (Nobody has suggested that, as far as I know.) Another, which is Ducheyne's approach, is despite the rather technical description, to treat the passage on pp. 38/39 as loose talk. But this means that Ducheyne must explain away Newton's invocation of the very contrast that grounds Ducheyne's original interpretation and he has not done so. Another way, which is the one I preferred, is that Newton means what he says and says so explicitly.
But does that leave me attributing to Newton a singular violation of his own methodological principle [A]? I don't think so. Because I deny that Newton holds [A] in the Treatise.
For, the point of Newton's mathematical way is to use it as a means to infer stuff about the nature of reality (including that Copernicus is true, etc.). This becomes clear if we look at what Newton does after he has explained the nature of centripetal forces. For example, he then goes on to "infer" that "That there are centripetal forces actually directed to the bodies of the Sun, of the Earth, and other Planets." (p. 10) In fact, Newton argues from "astronomical experiments" it "follows by geometrical reasoning, that there are centripetal forces, actually directed (either accurately or without conſiderable errour) to the centers of the Earth, of Jupiter of Saturn , and of the Sun." (12; emphasis added. Yhe nature of an astronomical experiment is of interest, but I leave it aside here)
So, it is misleading to use Newton's claims about the mathematical way as ruling out the possibility that Newton is making claims about the nature of reality. Rather, Newton treats them as a means to infer all kinds of things about what actually or really is the case. That is to say, the mathematical way is a mechanism to make inferences from theory-mediated measurements and (astronomical) experiments to the nature of reality.* Of course, to say that is not to do justice to the nature of Newton's inferential arguments (see Smith 2014).
That Newton does not treat the passage on pp. 38-39 as loose talk is also evinced by his illustrative claim directly following it that the "action betwixt the load-stone and iron is single, and is considered as single by the philosophers." (40; emphasis added) In fact, it is no coincidence that Newton draws attention to magnetism because his treatment here (of the analogy between magnetic and gravitational action) evokes, as I have argued in work unfamiliar to Ducheyne, Gilbert's (1651) De Mundo. That is to say, Newton draws attention to the fact that the very conceptual apparatus he is deploying is one used by other philosophers (including the expert on magnetism). That would be very odd if he were merely talking loosely.+
Of course, my position does entail that Newton came to see that his way of putting things in the Treatise was likely to be thought a kind of speculative talk he was ruling out when he rejected the explanatory demands (the "hypotheses") of the mechanical philosophers to put all explanations in terms of the size, figure, and motion of colliding bodies.
*I thank Marius Stan for urging this on me.
+Obviously, the argument of this post is compatible with the further claim (also defended by Ducheyne) that I misrepresent Newton's metaphysics.
Comments