The Impact Rules of Descartes' Physics

IN THE PRINCIPIA PHILOSOPHIAE OF 1644 Descartes develops seven rules for predicting what happens when one body collides with another and changes its speed or direction as a result of the impact. Since Descartes implies that these rules are derived from the three "laws of nature" of the Principia, and because the rules themselves appear to be evidently counterexperiential, two problems arise in attempting to understand the significance of these rules for Descartes' science: how does Descartes deduce the rules from the laws of nature, and to what extent are the rules compelling evidence that Descartes' scientific method is nonempirical? To facilitate discussion of the first question, translations of the relevant sections of the laws of nature are provided (they are referred to as L1-L3).1