The correspondence between Leibniz and Arnauld was judged by Leibniz himself to be very useful for understanding his philosophy. Historians have concurred in this judgment. Leibniz did not find any philosophy of independent interest in the letters Arnauld sent him. Historians have, for the most part, also concurred in this finding. I shall argue that on one set of issues at least — modal metaphysics and free will — Arnauld accomplished more than facilitating Leibnizian elucidations. He held his own in (...) this dispute. Indeed, were it not for the general sophistication and superior handling of such issues as identity, unity, and the nature of body enjoyed by the Leibnizian system, the Cartesian position on modal metaphysics and free will espoused by Arnauld might have won the day in the eyes of later philosophers. A proper appreciation of the Cartesian framework should also make it of considerable interest to philosophers presently at work on the metaphysics of modality. I shall argue that Descartes and some Cartesians like Arnauld espoused a strongly actualist doctrine. This means they thought that all philosophically interesting uses of possibles were analyzable into facts about actually existing things. (shrink)