Newton’s notion and practice of unification

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Abstract

In this paper I deal with a neglected topic with respect to unification in Newton’s Principia. I will clarify Newton’s notion (as can be found in Newton’s utterances on unification) and practice of unification (its actual occurrence in his scientific work). In order to do so, I will use the recent theories on unification as tools of analysis (Kitcher, Salmon and Schurz). I will argue, after showing that neither Kitcher’s nor Schurz’s account aptly capture Newton’s notion and practice of unification, that Salmon’s later work is a good starting point for analysing this notion and its practice in the Principia. Finally, I will supplement Salmon’s account in order to answer the question at stake.

Introduction

In this paper I try to capture Newton’s notion of unification and the actual practice of unification in his scientific work. It is a communis opinio that Newton’s unification of the terrestrial and heavenly bodies is an unprecedented achievement. In the literature on the nature and place of unification in scientific theories, philosophers of science therefore frequently refer to Newton’s mechanics. Nevertheless, few attempts have been made to really assess what Newton wrote/thought on the matter of unification in science (Newton’s notion of unification) and whether Newton actually practised what he preached (Newton’s practice of unification).1

I will use contemporary approaches on unification as tools of analysis. In the literature on unification in philosophy of science there are broadly two positions: the bottom-up approach––defended by the causalists––and the top-down approach––defended by the unificationists. According to the first approach explanation is local; according to the second it is global. The causalists claim that unification is ‘parasitic on the causal explanation of individual facts’ (Kitcher, 1985, p. 636). This approach was epitomised by Salmon (1984).2 The unificationists, on the other hand, endorse the view that causal explanation of particular occurrences recapitulates the ordering derived from the systematisation of regularities (Kitcher, 1985, p. 635). This tradition is primarily embodied by Kitcher (1989). Recently Gerhard Schurz defended a rather different top-down approach (Schurz, 1999).

First, I will argue that Kitcher’s account of unification does not provide an adequate perspective on Newton’s practice of unification (Section 2). I will omit a comparison between Newton’s notion of unification and Kitcher’s account. The reason for this is that there are few statements in Newton’s work that explicitly converge to or differ from Kitcher’s account. Second, I will argue that Schurz’s account is at odds with Newton’s notion and practice of unification (Section 3). Finally, I will argue that Salmon’s later synthesis of the two approaches (Salmon, 1998) is a good starting point for describing and understanding Newton’s notion and practice of unification (Section 4). In this section I attempt to characterise Newton’s notion and practice of unification. To sum up, in this paper I will deal with different but obviously interconnected questions. Did Newton conceive unification according to one of our contemporary approaches? Did he realise unification according to one of our contemporary approaches? Is the end product unified in the sense of one of our contemporary theories? What are the essential differences and/or similarities between Newton’s conception and practice of unification and ours?

Section snippets

Kitcher’s views on unification

Kitcher claims that behind the official view of the logical positivists, which states that explanation aims at expectability, there is also an unofficial view which regards explanation essentially as unification (Kitcher, 1981, p. 508). Kitcher tries to develop this idea. Our understanding of nature advances by increasing the degree of unification:

Science advances our understanding of nature by showing us how to derive descriptions of many phenomena, using the same patterns of derivation again

Schurz’s ideas on unification

In my presentation of Schurz’s ideas I will mainly focus on two propositions concerning unification and explanation which Schurz argues for and which can be considered as the core of his view. The four elements of an explanation, according to Schurz, are:

  • (i)

    the why-question (‘Why P?’);

  • (ii)

    the cognitive state C of the questioner;

  • (iii)

    the answer A, and finally;

  • (iv)

    the expanded or revised cognitive state C + A after receiving the answer.

Schurz further proposes a necessary condition (U) for explanation. This

Newton’s views positively described

In order to get a grasp on Newton’s notion and practice of unification I will focus on the analytic and the synthetic moment in Book III, the systema mundi, of the Principia. As Newton put it, the basic difficulty of natural philosophy is ‘to discover the forces of nature from the phenomena of motions and then to demonstrate the other phenomena from these forces’ (Newton, 1999, p. 382). The first conjunct refers to analysis, the second to synthesis. The analysis in the Principia consists in

Conclusion

Neither Kitcher’s not Schurz’s account seem to shed light on Newton’s notion and practice of unification. Of all modern alternatives Salmon’s later work on unification and causal explanation seems to be the closest to Newton’s way of conceptualising and performing unification. There are two notions of unification in Newton’s work that succeed each other:

(1) unification1 refers to unification which is established by identification of causal mechanisms (this is based on the premise that nature

Acknowledgements

The author wishes to thank the anonymous referees, Maarten Van Dyck, and especially Erik Weber for their valuable comments on previous versions.

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