In Bergsonism (1966), Deleuze develops the ideas of virtuality and multiplicity that will serve as the backbone of his later work. From Maimon's reading of Kant, we know that Deleuze needs to substitute the notion of the condition of the genesis of the real for the notion of conditions of possibility of representational knowledge. The positive name for that genetic condition is the virtual, which Deleuze adopts from the following Bergsonian argument. The notion of the possible, Bergson holds in Creative Evolution, is derived from a false problem that confuses the “more” with the “less” and ignores differences in kind; there is not less but more in the idea of the possible than in the real, just as there is more in the idea of nonbeing than in that of being, or more in the idea of disorder than in that of order. When we think of the possible as somehow “pre-existing” the real, we think of the real, then we add to it the negation of its existence, and then we project the “image” of the possible into the past. We then reverse the procedure and think of the real as something more than possible, that is, as the possible with existence added to it. We then say that the possible has been “realized” in the real. By contrast, Deleuze will reject the notion of the possible in favor of that of the virtual. Rather than awaiting realization, the virtual is fully real; what happens in genesis is that the virtual is actualized.
The Condition of the Genesis of the Real+quote