The Direction of Motion: Occasionalism and Causal Closure from Descartes to Leibniz

Leibniz ascribed to Descartes a version of what is now termed the change-of-direction account of voluntary motions, according to which the soul can only determine the body’s motions by changing their directions. In spite of some recent discoveries, the history of this doctrine remains largely unknown. Sections 1 through 5 reconstruct the development of the change-of-direction account among early Cartesians (Regius, Clerselier, Clauberg, La Forge, and Cordemoy) and conclude that the different versions of this account advanced by these authors reveal their different degrees of commitment to occasionalism. Section 6 discusses Garber’s and McLaughlin’s interpretations, concluding that the change-of-direction account prevents the occasionalist world from being causally closed – which indeed constitutes the major divide between occasionalism and Leibnizian harmonism. In section 7, Christian Wolff’s attempt to revise occasionalism by reinforcing the change-of-direction account suggests a reassessment of its real import and implications.