With difference or intensity instead of identity as the ultimate philosophical one could arrive at the crux of Deleuze’s use of the Principle of Sufficient Reason in Difference and Repetition. At the beginning of the first chapter, he defines the quadruple yoke of conceptual representation identity, analogy, opposition, resemblance in correspondence with the four principle aspects of the Principle of Sufficient Reason: the form of the undetermined concept, the relation between ultimate determinable concepts, the relation between determinations within concepts, and the determined object of the concept itself. In other words, sufficient reason according to Deleuze is the very medium of representation, the element in which identity is conceptually determined. In itself, however, this medium or element remains different or unformed (albeit not formless): Difference is the state in which one can speak of determination as such, i.e. determination in its occurrent quality of a difference being made, or rather making itself in the sense of a unilateral distinction. It is with the event of difference that what appears to be a breakdown of representational reason is also a breakthrough of the rumbling ground as differential element of determination (or individuation). Deleuze illustrates this with an example borrowed from Nietzsche:
Instead of something distinguished from something else, imagine something which distinguishes itself and yet that from which it distinguishes itself, does not distinguish itself from it. Lightning, for example, distinguishes itself from the black sky but must also trail behind it . It is as if the ground rose to the surface without ceasing to be the ground.
Between the abyss of the indeterminate and the superficiality of the determined, there thus appears an intermediate element, a field potential or intensive depth, which perhaps in a way exceeds sufficient reason itself. This is a depth which Deleuze finds prefigured in Schelling’s and Schopenhauer’s differend conceptualization of the ground (Grund) as both ground (fond) and grounding (fondement). The ground attains an autonomous power that exceeds classical sufficient reason by including the grounding moment of sufficient reason for itself. Because this self-grounding ground remains groundless (sans-fond) in itself, however, Hegel famously ridiculed Schelling’s ground as the indeterminate night in which all cows are black. He opposed it to the surface of determined identities that are only negatively correlated to each other. By contrast, Deleuze interprets the self-grounding ground through Nietzsche’s eternal return of the same. Whereas the passive syntheses of habit (connective series) and memory (conjunctions of connective series) are the processes by which representational reason grounds itself in time, the eternal return (disjunctive synthesis of series) ungrounds (effonde) this ground by introducing the necessity of future becomings, i.e. of difference as ongoing differentiation. Far from being a denial of the Principle of Sufficient Reason, this threefold process of self-(un)grounding constitutes the positive, relational system that brings difference out of the night of the Identical, and with finer, more varied and more terrifying flashes of lightning than those of contradiction: progressivity.
The breakthrough of the ground in the process of ungrounding itself in sheer distinction-production of the multiple against the indistinguishable is what Deleuze calls violence or cruelty, as it determines being or nature in a necessary system of asymmetric relations of intensity by the acausal action of chance, like an ontological game in which the throw of the dice is the only rule or principle. But it is also the vigil, the insomnia of thought, since it is here that reason or thought achieves its highest power of determination. It becomes a pure creativity or virtuality in which no well-founded identity (God, World, Self) remains: [T]hought is that moment in which determination makes itself one, by virtue of maintaining a unilateral and precise relation to the indeterminate. Since it produces differential events without subjective or objective remainder, however, Deleuze argues that thought belongs to the pure and empty form of time, a time that is no longer subordinate to (cosmological, psychological, eternal) movement in space. Time qua form of transcendental synthesis is the ultimate ground of everything that is, reasons and acts. It is the formal element of multiple becoming, no longer in the sense of finite a priori conditioning, but in the sense of a transfinite a posteriori synthesizer: an empt interiority in ongoing formation and materialization. As Deleuze and Guattari define synthesizer in A Thousand Plateaus: The synthesizer, with its operation of consistency, has taken the place of the ground in a priori synthetic judgment: its synthesis is of the molecular and the cosmic, material and force, not form and matter, Grund and territory.