Time for Empiricist Metaphysics
To what extent are the details of empirical enquiry relevant for the metaphysics of time ? I shall argue that they are deeply, utterly, and inextricably entwined, and moreover that they became so as a consequence of philosophical moves made by Newton in his Principia} Prior to the Principia, general questions about the nature and structure of time, such as whether or not time is merely an aspect of material change, whether there is one time or many, whether time is inherently metrical, and so forth, could be (and were) appropriately addressed via arguments based on broadly a priori considerations. In the wake of Newton’s Principia, this is no longer the case. Newton showed how the answers to these questions depend on the intricate details of empirical enquiry. Those of us who are interested in the metaphysics of time are not free to pretend that the philosophical moves made by Newton were never, in fact, made. He made these moves, and this paper is about their implications for the metaphysics of time.
In the recent Blackwell Companion to Philosophy of Time (2013), there is a section on “The History of the Philosophy of Time,” and there, between a chapter on creation and eternity in medieval philosophy and one on classical empiricist discussions of time, we find a chapter on Newton. In this chapter, Eric Schliesser asks us to pause with Newton, and to look in more detail at his contributions to 
the philosophy of time. Instead of taking Newton’s physics, and then looking at what other philosophers have to say about time in the light of his physics, we look at what philosophical moves Newton himself made. I think Schliesser is right that this is worth doing, and I claim that Newton’s empirical methods reach deeply into metaphysical questions concerning the nature and structure of time. For philosophers with an interest in the metaphysics of time, Newton’s Principia needs to be read as a philosophical text, offering contributions to an empiricist metaphysics of time.
I begin from three distinctions that Newton made at the beginning of his Principia, in the famous scholium on time, space, place, and motion. There, he said that we should distinguish between absolute and relative, true and apparent, and mathematical and common, for each of time, space, place, and motion. I outline these distinctions as they apply to time (section 2), and then discuss Schliesser’s (2013) interpretation of Newton’s distinction between absolute and true time (section 3), explaining why I think a different approach is needed. I then build toward the positive conclusions that I want to draw. I begin by offering an alternative interpretation (section 4), according to which Newton is drawing on existing terminology and implicit conceptual distinctions in order to make explicit and systematic a three-way set of distinctions concerning the nature and structure of time. In so doing, he makes a contribution to the philosophy of time. I then argue that (a) these distinctions are empirically accessible (see section 5), and (b) all three distinctions are necessary for setting up the project of the Principia (see section 6). It follows from this, I argue, that certain questions concerning the nature and structure of time become empirically tractable through the pursuit of that project, or some appropriately similar project. By situating Newton’s Principia in the appropriate philosophical context (section 7), we can read the Principia as a direct contribution to the metaphysics of space, time, matter, and motion, and as offering an empiricist metaphysics of a particular kind. I claim that Newton refined the conceptual distinctions appropriate for asking questions about the nature and structure of time, and transformed the methodology by which such questions should be addressed, and I show this in detail for each of the three distinctions he makes at the outset of the Principia (see section 8). I conclude by drawing together the results of the preceding sections, and then use the specific example tackled in this paper to suggest some more general lessons about how philosophers should approach the relationship between metaphysics and empirical science (section 9).
Time for Empiricist Metaphysics