Newton's critique of Descartes's Theory of Motion

Alex W Carmical, Purdue University


Newton’s Critique of Descartes’s Theory of Motion examines Isaac Newton's critique of René Descartes’s theory of motion as well as the former’s positive views regarding the metaphysics of space and motion. At the heart of this monograph is an interpretation of a family of arguments taken from the unfinished, posthumously published manuscript, De Gravitatone et Aequipondio Fluidorum, as well as from a scholium to a definition of one of the technical terms of his theory of dynamics. Against the traditional interpretation, which argues that Newton uses these arguments to support the conclusion that substantival space exists, I contend that these arguments are interpreted correctly only if they are placed in the context of a sustained critique of Descartes’s theory of motion. Their aim is more modest in that they try to show that Descartes’s theory is false. Consequently, these arguments should be evaluated according to whether they rebut the Cartesian position and not according to whether they establish the thesis of substantivalism. The first three chapters set the stage for this evaluation. Chapter One—Customary Space-time Primer—emphasizes the distinction between two kinds of discourse. On the one hand one may talk about mathematical entities, e.g., differentiable manifolds and the functional “structures” defined upon them; and on the other he may talk about the ontology that is, in some way, modeled by the mathematics. The line between the two is sometimes blurred and, so, confusion results. The other objective of the Customary Space-time Primer is to survey the various space-time structures in order to prepare the way for Newton’s Argument from the Meaning of Motion (Chapter Five) and his Argument from the Principle of Inertia (Chapter Six). Chapter Two—Newton’s Doctrine of Space—presents Newton’s positive views regarding the nature of space. Since Newton regards the mobility of Cartesian places as the fundamental flaw of Descartes’s theory, this chapter examines his arguments for the immobility of the places that make up Newtonian space. In the final section, I present what I take to be Newton’s argument for the existence of substantival space, an argument that has a theologico-metaphysical basis rather than the physico-metaphysical basis some commentators ascribe to other of Newton’s arguments. Chapter Three—The Cartesian World—argues that, given his metaphysical commitments, Descartes is confronted with a dilemma: either motion is defined in the “vulgar sense,” i.e., with respect to some noncircumambient bits of the plenum, or it is defined in the “philosophical sense,” i.e., as translation out of one neighborhood of circumambient bodies into another. If defined in the former sense, then he is impaled on the horn of the Problem of Arbitrariness; and if defined in the latter sense, then he is impaled on the horn of the Problem of Impoverished Space-time Structure. Newton, confronted with what appear to be the intractable difficulties of the Cartesian account of motion, can be seen as postulating absolute space as a way out of this dilemma. In the second part of this dissertation, I turn to Newton’s critical program. Specifically, I examine Newton’s Bucket Experiment Argument, his Argument from the Meaning of Motion and his Argument from the Principle of Inertia. Chapter Four—Myth of the Bucket Experiment—takes up the Bucket Experiment Argument and contends that, contrary to the “Received View,” Newton did not intend this as a positive argument for the existence of substantival space; rather he intended this argument to be a refuter of Descartes’s philosophical account of place and motion. Chapter Five—Argument from the Meaning of Motion—presents a reductio of Descartes’s theory of motion, one that tries to show that, if the circumambient bodies that define Descartes’s philosophical places are taken as the basis for defining (absolute) motion, then “Cartesian motion is not motion.” I argue that, as presented Newton’s argument begs the question against Descartes. But a reconstructed version succeeds in reducing the Cartesian position to absurdity. Chapter Six—Argument from the Principle of Inertia—considers another reductio of Descartes’s theory. In this case, Newton tries to show that Descartes’s theory of motion is incompatible with his principle of inertia. Then I present one of Edward Slowik’s attempts to salvage the Cartesian programme and argue that, ultimately, it fails to do so.




Curd, Purdue University.

Subject Area

Philosophy of Science|Philosophy

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