Descartes and His Critics on Space and Vacuum A
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DESCARTES AND HIS CRITICS ON SPACE AND VACUUM A Dissertation Submitted to the Graduate School of the University of Notre Dame in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy by Joseph Raphael Zepeda Karl Ameriks, Co-Director Anja Jauernig, Co-Director Graduate Program in History and Philosophy of Science Notre Dame, Indiana July 2009 © Copyright by Joseph R. Zepeda 2009 All rights reserved DESCARTES AND HIS CRITICS ON SPACE AND VACUUM Abstract by Joseph Raphael Zepeda This study is an interpretation of Descartes’ theory of space and vacuum. Descartes famously holds that space is identical to matter, and that a vacuum or empty space is logically impossible. These positions earned Descartes a great deal of criticism from philosophers during the seventeenth and eighteenth centuries. Two main strands of criticism are dealt with here. First, Descartes was charged with dogmatism for holding that rival notions of space were inconceivable, a position for which he seems to have no good arguments. Second, some philosophers claimed that Descartes is guilty of inconsistency: his position on the vacuum, they said, was incompatible with his theory of the metaphysics of extended substance. This dissertation comprises a comprehensive interpretation of Descartes’ treatment of space and vacuum, particularly in the Principles of Philosophy (1644). A new reading of the discussion of place and space in Principles Part II is articulated and defended; the result is a fundamental rethinking of what Descartes means by the claim that body and space are identical. This reinterpretation provides the basis for the culminating point of the study. Descartes’ position on the vacuum is discussed in relation to a number of different understandings of what a vacuum might be. The different Joseph R. Zepeda arguments he offers concerning the vacuum are analyzed and related to each other. Two chapters are devoted to objections raised by Arnauld, Henry More, and Spinoza. The implications of these objections for Descartes’ theory of extended substance are pursued in these chapters, and direction for further research on this topic is discussed in an appendix. The central thesis argued here is that Descartes’ position on space and vacuum is more plausible in its context than has been recognized. It turns out that Descartes takes great care to address the strengths of his opponents’ positions on space and vacuum, and that he has an argument for his view involving an appeal to ontological economy or simplicity. His position on this topic, which is commonly taken to be a paradigmatic example of dogmatism, is argued for more plausibly, and more responsibly, than has previously been recognized. For my wife Julie ii CONTENTS Introduction..............................................................................................................1 Chapter One: Descartes on the Concept of a Space...............................................14 Chapter Two: Against the Vacuum........................................................................46 Chapter Three: Descartes’ Critics I: Arnauld and Henry More.............................96 Chapter Four: Descartes’ Critics II: Spinoza.......................................................127 Chapter Five: Matter and Space according to the Order of Reasons...................165 Appendix: The Metaphysics of Extended Substance in Descartes......................208 Bibliography ....................................................................................................... 223 iii INTRODUCTION Descartes famously holds that body and space are identical, and that an empty space or vacuum is logically impossible. Perhaps it would be better to say that he infamously holds these views; certainly there was no lack of criticism directed toward them, even by his followers, in the seventeenth and eighteenth centuries. Locke offers a fairly typical response in the Essay, in his discussion of the idea of space or extension: There are some that would persuade us, that Body and Extension are the same thing; who either change the Signification of Words, which I would not suspect them of, they having so severely condemned the Philosophy of others, because it hath been too much placed in the uncertain meaning, or deceitful obscurity of doubtful or insignificant Terms.1 Locke drives home his point here by referring to Descartes’ criticism of the Scholastic Aristotelians—these are the “others” who based their philosophy on “doubtful or insignificant Terms.” The point, then, is that the Cartesian position is based on nothing but a stipulated definition. Locke goes on to enumerate the ways in which our actual idea of space differs from that of body. This is not an idiosyncratic line of thought on Locke’s part. Among the major early modern philosophers there are few who do not think that Descartes’ position on space and vacuum is either badly argued, hopelessly dogmatic, or both. Among those who do accept the Cartesian 1 John Locke, Essay concerning Human Understanding II.XIII.11, ed. Peter Nidditch (Oxford: Clarendon, 1975): 171. 1 position on the vacuum, most find this incompatible with other aspects of his metaphysics of extension: Spinoza is a notable example, but some important Cartesians fit the description as well. This study aims to provide an interpretation of these notorious theses in Descartes, chiefly as they are articulated in the Principles of Philosophy. Some crucial aspects of Descartes’ view on space and matter have been misunderstood, and once this has been remedied the case for his position against the then-available alternatives is significantly strengthened. Moreover, it turns out that Descartes can plausibly resist the charges of Spinoza and others that his theory of extended substance is incompatible with his position on the vacuum. Before specifying in more detail the context, content and aims of the following chapters, it is important to clarify what this study does not address. The question of the existence or possibility of the vacuum is well-known as a historical battleground between rationalism and empiricism, broadly speaking. Descartes and Pascal on the barometer, Hobbes and Boyle on the air pump; there is a long history of taking these debates as case studies for the conflict between different approaches to natural philosophy.2 This study addresses criticisms of Descartes’ position, but focuses on those which engage Descartes largely on his own terms, rather than those which call into question the whole project of rationalist natural philosophy. This does not rule out some who are normally classified as empiricists; some objections from 2 In the recent decades the literature has embraced a more nuanced view of these debates, a view influenced by the suspicion of naïve or dogmatic empiricism in the history and philosophy of science. For a good discussion of Pascal and Descartes, see Daniel Garber, Descartes’ Metaphysical Physics (Chicago: University of Chicago Press, 1992): 136-143. A now-classic account of the Hobbes- Boyle debate is Stephen Shapin and Simon Schaffer, Leviathan and the Air Pump: Hobbes, Boyle and the Experimental Life (Princeton: Princeton UP, 1989). 2 Locke will receive sustained discussion here. Debates about the place of experiment in natural science, however, are not the topic of this study. Descartes’ views on space have also been examined and criticized with respect to his physics. For example, the issues brought up by Newton in his famous scholium on space and time in the Principia, or by Leibniz and Clarke in their equally famous correspondence, are relevant in assessing Descartes’ views on space taken broadly, notwithstanding the risk of anachronism in interpretation. Generally, it is important to ascertain the degree to which Descartes’ laws of motion are compatible with his rejection of a body-independent space. A recent monograph by Edward Slowik addresses these and related topics, with an eye towards reconstructing, as far as possible, a plausible and coherent relational space-time theory to accompany Descartes’ physics.3 The present study, however, is concerned with a different set of arguments. Descartes’ explicit treatment of space and place deals only with general features of bodies and motion, rather than the particular demands of any developed physics, and it is the former that is addressed here. To the extent that Descartes is defended in this study, it is not an assessment of his physics or the spacetime theory it requires. Descartes’ position on space and vacuum is supposed to be a result of his definition of matter or body, so it is worthwhile to sketch out some of the relevant background within the Cartesian corpus. A conception of matter as having only geometrical features, as mere extension, is a persistent feature of Descartes’ thought, 3 Edward Slowik, Cartesian Spacetime: Descartes’ Physics and the Relational Theory of Space and Motion (Dordrecht: Kluwer, 2002). 3 from the early Rules for the Direction of the Mind (1628) all the way through to the Principles (1644). In the Regulae this is tied up with Descartes’ ambitions for a universal method of problem-solving. Extension is something like a maximally intelligible medium in terms of which problems can be reformulated, classified and solved, if possible. It is contested whether there is any significant continuity between the methodology described in the Regulae and the more schematic rules proposed in later works such as the Discourse on Method or the Replies to Objections to