Still, despite Deleuze's distancing from creative evolution, something substantial persists across his changing relation to both Bergson and biology.
Namely, his commitment to a notion of internal difference, or difference in itself. This commitment motivates Deleuze's initial adherence to Bergson's creative evolutionism no less than his later "break" with Bergson over the status of intensity as well as the correlated model of creative involution he develops together with Guattari. The initial impetus driving Deleuze's effort to rehabilitate the fraught notion of the elan vital and with it, the very career of Bergson as philosopher, was nothing other than the notion of internal difference. As he reconstructs it in his 1956 essay, "Bergson's Conception of Difference," and then again in his 1966 Bergsonism, the elan vital introduces an explosive force internal to the process of evolution (internal difference) that is capable of accounting for the positive power of time as a source of creative invention. With the progress of his own
philosophical career, Deleuze soon found reason to temper his initial adherence to Bergsonism--and specifically, to Bergson's
derivation of internal difference from qualitative difference--without in any way abandoning his own commitment to
As early as Difference and Repetition (1968), Deleuze traces qualitative difference or difference in kind (together with quantitative difference or difference in degree) to a fluid continuum of intensity, thereby eschewing Bergson's argument that qualitative difference is itself one of two tendencies being differentiated and thus, a tendency internal to difference that, as Deleuze puts it, "show[s] the way in which a thing varies qualitatively in time".