The Metaphysical Roots of Cartesian Physics: The Law of Rectilinear Motion

This paper presents a detailed account of Descartes' derivation of his second law of nature—the law of rectilinear motion—from a priori metaphysical principles. Unlike the other laws the proof of the second depends essentially on a metaphysical assumption about the temporal immediacy of God's operation. Recent commentators (e.g., Des Chene and Garber) have not adequately explained the precise role of this assumption in the proof and Descartes' reasoning has continued to seem somewhat arbitrary as a result. My account better reveals the dependence of the second law on fundamental principles about time and causality.