Philosophical Mechanics in the Age of Reason
Abstract
Philosophical Mechanics in the Age of Reason argues that the Enlightenment was a golden age for the philosophy of material bodies, and for efforts to integrate coherently a philosophical concept of body with a mathematized theory of mechanics. Thereby, it articulates a new framing for the history of 18th century philosophy and science. It explains why, more than a century after Newton, physics broke away from philosophy to become an autonomous domain. And it casts fresh light on the structure and foundations of classical mechanics. Among the figures studied are Malebranche, Leibniz, Du Châtelet, Boscovich, and Kant, alongside d’Alembert, Euler, Lagrange, Laplace, and Cauchy.
... Within France this research program became extremely influential, and some notable successes were achieved. However, there was no complete agreement on the properties of these molecules, which were often seen as point particles but sometimes as having a certain extension; and despite the fact that the explicit aim of this program was to reduce all natural phenomena to the motion of molecules, in practice even the Laplacians found it more convenient to treat matter as continuous in some of their calculations (Brading & Stan 2024). 2 After a brief period of great success, Laplace's program collapsed between 1815 and 1825, and most physicists came to agree that its ontology of point particles was too restrictive to account for all natural phenomena (Fox 1974). ...
... Therefore, how a certain physicist treated matter in his calculations did not necessarily have to match his views on the ultimate constitution of matter. For example, in the 1820s, Cauchy worked with a continuum conception of matter, despite his conviction that matter is actually molecularly constituted -his ontological commitments did not seem to matter to his physics (Brading & Stan 2024). ...
The idea that all physical phenomena should ultimately be reducible to matter and motion was influential throughout the nineteenth century, although this ideal was never realized and never without critics. But could the notion of matter itself be understood? A unified conception of matter was lacking in nineteenth century physics. Physicists used different conceptions of matter, and debated the question of the true nature of matter on the basis of philosophical as well as empirical arguments; it turned out to be very challenging to develop a conception of matter that was consistent with experimental findings as well as philosophically satisfactory. Towards the end of the nineteenth century, physicists increasingly rejected the question of the true nature of matter, arguing that this question was irrelevant for physics or altogether meaningless. This was sometimes seen as an emancipation of physics from philosophy, and sometimes as a result of philosophical reflection on physics.
Newton’s Principia reconceptualizes rational mechanics and physics, and offers a novel unification of these heretofore distinct disciplines. In this paper, I argue for a reading of the Principia that insists on a strict distinction between the rational mechanics (in Books 1 and 2) and the physics (in Book 3), in which the Definitions and the Axioms/Laws play a surprising dual role that both distinguishes the rational mechanics from the physics and unifies them into a single project: a philosophical mechanics.
Early modern foundations for mechanics came in two kinds, nomic and material. I examine here the dynamical laws and pictures of matter given respectively by Newton, Leibniz, and Kant. I argue that they fall short of their foundational task, viz. to represent enough kinematic behavior; or at least to explain it. In effect, for the true foundations of classical mechanics we must look beyond Newton, Leibniz, and Kant.
Botanical and zoological systematics in the early modern period – from Cesalpino in the sixteenth century to Linnaeus and Jussieu in the eighteenth century – was a two-faced and latently contradictory enterprise: It was, on the one hand, an empirical naturalistic science and, on the other hand, aligned with metaphysical principles concerning the order of natural things which form, according to these principles, a continuous chain of beings and a scala naturae, arranged according to degrees of their perfection. According to these principles, and especially according to that of continuity, no botanical or zoological classificatory system could establish anything but an artificial and unnatural order of plants and animals. The chapter illuminates these contradictions and tensions and traces the development of biological insights that eventually, at the turn of the eighteenth century, led systematists to renounce these metaphysical principles.
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