 But the organismic elements in Diderot’s materialism and vision of the body lead him to challenge Helvétius’ program of reform, which asserts, on the basis of an empiricist and specifically sensationalist epistemology, that human beings really are fully modifiable “blank slates”, modifiable in terms of what we call stimuli and responses. Interestingly, it is by denying this “full modifiability” that Diderot can defend a certain notion of individuality. The fact that individuals differ from each other at the level of their organisation grants them a degree of self-determination. “Every day, I see men who prefer to die rather than to correct themselves” (DPV XVIII: 344). That is, what Diderot calls “modifiability”, which might better be termed “corrigibility”, has limits, and these limits do not just reflect some kind of blunt innatism (whether of genetic heritage or of character), but rather a degree of individuality, including at the level of agency. Biologically, Diderot often stressed the enormous variation of traits such as intelligence from one individual to another, noting that the difference between an “idiot” and a “genius” hinges on tiny shifts in “brain fibers”. There is more difference, he insists, between one individual and another in terms of intelligence than between a human being and an animal (DPV XXIV: 299). But there is no sharp divide between the biological and the personal, for Diderot.