This paper examines the young Kant’s claim that all motion is relative, and argues that it is the core of a metaphysical dynamics of impact inspired by Leibniz and Wolff. I start with some background to Kant’s early dynamics, and show that he rejects Newton’s absolute space as a foundation for it. Then I reconstruct the exact meaning of Kant’s relativity, and the model of impact he wants it to support. I detail (in Section II and III) his polemic engagement with Wolffian predecessors, and how he grounds collisions in a priori dynamics. I conclude that, for the young Kant, the philosophical problematic of Newton’s science takes a back seat to an agenda set by the Leibniz-Wolff tradition of rationalist dynamics. This results matters, because Kant’s views on motion survive well into the 1780s. In addition, his doctrine attests to the richness of early modern views of the relativity of motion.

In this article, I discuss how Leibniz’s first correspondence with Malebranche from early 1676 can shed new light on the notorious “all-things-are-one”-passage (ATOP) found in the Quod ens perfectissimum sit possibile from late 1676—a passage that has been taken as an expression of monism or Spinozism in the young Leibniz. The correspondence with Malebranche provides a deeper understanding of Leibniz’s use of the notions of “real distinction” and “separability” in the ATOP. This forms the background for a discussion of Leibniz’s commitment to the monist position expounded in the ATOP. Thus, on the basis of a close analysis of Leibniz’s use of these key terms in the Malebranche correspondence, I provide two possible, and contrary, interpretations of the ATOP, namely, a “non-commitment account” and a “commitment account.” Finally, I explain why I consider the commitment account to be the more compelling of the two.