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Journal of the History of Philosophy 44.2 (2006) 321-322
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Most scholars believe that the problem of infinite divisibility that plagued early modern natural philosophy was an entirely mathematical issue and, therefore, resulted from the short-comings of early modern mathematics. Accordingly, advances in geometry, topology and the logic of infinity are often thought to lay this debate to rest, thereby reducing it to some quaint footnote in the history of natural philosophy. Thomas Holden, however, through thorough textual and philosophical analysis, convincingly argues that this debate was more metaphysical in nature than previously supposed. He shows how the various paradoxes concerning the structure of matter stem from two widely-accepted theses central to the new science. The first resulted from the early modern method of applying the principles of geometry to physics. This geometrical method dictated that bodies are metaphysically divisible (m-divisible) in infinitum, because they occupy regions of space that can, at least by the power of God, be subdivided into those parts occupying corresponding sub-regions of space, and those sub-parts into those sub-sub-parts occupying their respective corresponding sub-sub-regions of space in infinitum. The other thesis is that "the parts of material bodies are each concrete existents in their own right" (3). Such actual parts exist prior to any act of division, whereas parts that are only potential would not exist prior to division but only after a divisive act has occurred. Holden argues that the actual parts doctrine was a metaphysical thesis just as fundamental to Enlightenment natural philosophers as the geometrization of matter. Indeed, it is these two theses that came into conflict and gave rise to a plethora of antimonies at the heart of the new science.
Holden should be applauded for the skill he employs in challenging the received scholarship. In chapter 1, after some historical and terminological preliminaries, Holden reconstructs several of the more popular paradoxes of material structure found throughout the period's vast literature and successfully shows how these paradoxes would not arise if the problems of material structure were merely mathematical. He shows how the metaphysical doctrine of actual parts gave rise to these difficulties because of its conflict with the assumed geometrical doctrine that extension is infinitely m-divisible. For example, some thought it followed from the actual parts doctrine that there must be an actual infinity of parts, because actual parts exist prior to any process of division and, therefore, in order for both actual parts and infinite m-divisibility to be true, there must be an actual infinity of parts. This raised issues about the intelligibility and piety of an actual infinite as well as issues about equal and unequal infinities, e.g., half an infinite number of parts would still be infinite but half as much as the whole collection of parts. Hence, this and other paradoxes would not arise in the absence of the actual parts doctrine, and so the debate is more metaphysical in nature than previously supposed. [End Page 321]
Chapter 2 examines in more detail the actual parts metaphysic and how it leads to tension with infinite m-divisibility. Chapter 3 examines various "short-circuit" arguments designed to undermine the actual parts doctrine. And chapter 4 examines the actual parts doctrine via the argument from composition found in Kant's pre-critical work, Physical Monadology. In chapter 5, Holden briefly examines the potential parts doctrine and how some actual-parts partisans tried to undermine it. It is eventually concluded that actual-parts and potential-parts advocates are at an impasse due to the question-begging nature of their respective arguments. Finally, chapter 6 is "something of an addendum" (74), since it examines a fascinating synthesis of the two conflicting positions, viz. the Kant-Boscovich force-shell atom theory.
Given that the book is about material structure, it is a propos that my critical comment is about the structure of the book. It seems...