In a text written during his stay in Paris, Leibniz, to deny ontological reality to relations, employs an argument well known to the medieval thinkers and which later would be revived by Francis H. Bradley. If one assumes that relations are real and that a relation links any property to a subject – so runs the argument – then one falls prey to an infinite regress. Leibniz seems to be well aware of the consequences that this argument has for his own metaphysical views, where the relation of inherence (‘inesse’) plays such a central role. Thus, he attempts first to interpret the relation of inherence as something ‘metaphoric’, originating from our ‘spatial way’ of looking at the surrounding world; and then he tries to reduce it to the part-whole relation which clearly he considers weaker, from the ontological point of view, than that of ‘being in’.

In discussion of Leibniz’s philosophical methodology Donald Rutherford defends the view that Leibniz regarded metaphysics as an a priori demonstrative science. In the course of this discussion Rutherford isolates and tries to deflect a significant challenge for his view, namely the observation that in many of his mature writings on metaphysics Leibniz appears to defend his views by means of a posteriori arguments. I present some prima facie difficulties with Rutherford’s position and then offer an alternative account of how Leibniz thought he needed to establish metaphysical claims. My suggestion is that the challenge that Rutherford poses may be best answered by attending to the fact that Leibniz recognized a kind of metaphysical enquiry, ‘real metaphysics’, that is essentially a posteriori, in virtue of the fact that it is concerned not just with possible kinds of beings, but with the kinds of beings that God actually created.

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.

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.