References to Leibniz's philosophy appear constantly throughout Deleuze's work. Despite often repeating the same themes, we find marked differences in tone, as if Deleuze is unable to arrive at a conclusive judgement. This book explores these various engagements and tries to account for these shifts in tone. Ultimately it will argue that focusing on Deleuze's interpretation of Leibniz – both his appropriations and his criticisms – helps us to understand some key moments in Deleuze's own philosophical development. A close reading, emphasising the particular context and terminology of Leibniz's work, will open a narrow point of access into some of the most difficult areas of Deleuze's philosophy. In the course of this reading, it will become clear that it is precisely Leibniz's ambiguous status for Deleuze which makes an investigation into their relationship so fruitful: by not only explaining Leibniz's positive influence, but also pinpointing the precise grounds for their eventual divergence, we hope to better articulate some of Deleuze's own philosophical priorities.

Any close reading must thus begin by taking this ambiguous status seriously. There are two opposing tendencies that allow us to identify two distinct sides to Leibniz's philosophy, or indeed, the presence of two distinct ‘Leibnizes’, in Deleuze's readings. Leibniz, in fact, is not unused to undergoing such partitions. The first biography of Leibniz, in a eulogy by Bernard Fontenelle (the secretary of the Académie des Sciences in Paris upon Leibniz's death), likens his propensity for broad study to a charioteer expertly managing each of his horses. Fontenelle's eulogy insists that we decompose and ‘make many geniuses out of one Leibniz’, a maxim which has generally set the standard for later scholarship. But where traditionally the lines of Leibniz's decomposition have been drawn according to discipline (Leibniz the philosopher, Leibniz the logician, Leibniz the mathematician, and so on), in Deleuze's reading we find Leibniz split by two opposing tendencies that are not only philosophical but also theological, moral and political.

We’ll briefly introduce these two tendencies or ‘two Leibnizes’ by looking at the first available of Deleuze's extended discussions of Leibniz. Qu’est-ce que fonder? (What is Grounding? or What is it to Ground?) was a lecture course given by Deleuze in 1956.