Titled ‘The Theory of Expression in Leibniz and Spinoza’, Deleuze's conclusion to Expressionism in Philosophy: Spinoza gives Leibniz a new, central role that was lacking in our discussions in the last chapter. While the three discussions of Leibniz we’ve looked at so far appeared incidental, they are now drawn together by Deleuze under a new heading: the three ‘fundamental determinations’ of being, knowing and acting. These correspond to God and God's nature, to adequate ideas, and to bodies imbued with force (EPS 321). At the same time, sufficient reason, a concern for which had motivated these discussions, is now itself given a clearer formulation by being distributed across these three domains. Thus, Deleuze writes, sufficient reason has three branches, the ratio essendi or reason for essence, the ratio cognoscendi or reason for knowing, and the ratio fiendi or agendi or reason for producing or acting (EPS 322).It is in these three domains that Deleuze locates a crucial role for the concept of expression, which he now considers just as central to Leibniz as to Spinoza, and which constitutes the heart of their shared anti-Cartesian reaction.

Leibniz's appearances in the main text were dominated by references to his theological commitments. Here in the conclusion, by contrast, a different side of Leibniz starts to come to the fore. The Leibniz we find here is much closer to the Leibniz that Deleuze puts to work at crucial stages in Difference and Repetition and Logic of Sense. How do we explain Leibniz's sudden transformation in Deleuze's work? There are various possibilities. Although Expressionism in Philosophy: Spinoza was published the same year as Difference and Repetition, Dosse points out that it was ‘practically finished in the late 1950s’ (Dosse 2013: 118). It is possible, then, that the conclusion was written significantly later than the main text. And perhaps in the interval Deleuze had come to a more developed understanding and appreciation of Leibniz's philosophy. On the other hand, perhaps Deleuze had always had this more radical version of Leibniz in mind, but suppressed it in the main text until it was relevant, or because he wanted to emphasise Spinoza's originality.