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 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 this article, I propose a conjecture concerning the transmission of Spinoza’s Korte Verhandeling (KV) in the 1670s involving Leibniz. On the basis of a report about Spinoza’s philosophy written down by Leibniz after some conversations with Tschirnhaus in early 1676, I suggest that Tschirnhaus may have had in his possession a manuscript copy of KV and that his account of Spinoza’s doctrine to Leibniz was colored by this text. I support the hypothesis partly by means of external evidence, but mainly through a comparative analysis of Leibniz’s report and the doctrine contained in KV, showing that the report in important respects corresponds better to this text than to Ethics. I finally point to the importance that this hypothesis, if true, would have for our knowledge of Tschirnhaus’ role in the first diffusion of Spinoza’s philosophy outside Holland and for our understanding Leibniz’s reception of Spinoza in the mid-1670s.