 Diderot’s eclecticism and materialism nevertheless remain in tension, since eclecticism is not conducive to foundational ontological commitments, while materialism, whatever the specific matter theory it bases itself on, seems to be a paramount case of a foundationalist ontology. What is real is matter, or perhaps, what the sciences of matter declare to be real (and this can vary widely, from the chemistry of mixts which Diderot was so fascinated by [Pépin 2012], to the nascent biology he seems to be calling for in the Pensées sur l’interprétation de la nature, as we discuss below, to physics). And yet, as a series of propositional pensées offered to readers without any interconnecting discursive bridge between themes, this text also propounds eclecticism methodologically, in contrast to a systematically presented set of premises, arguments and conclusions. This play between imaginative possibility and demonstrative certainty, and between what rationally must be and what language is capable of capturing and conveying in human terms is characteristic of Diderot’s thought overall, and his philosophy cannot be shorn of this conceptual linguistic instability without destroying its power.