In this talk I want to address Denis Diderot’s natural philosophy, namely his explanation of man and the human body, and investigate what he is doing when he explains man. In his philosophy, Diderot does both, denoting the body as a machine (Le Rêve de d’Alembert) and negating that the body is a machine (Pensées sur l'interprétation de la nature, Éléments de physiologie). I would like to argue that Diderot does not believe the man to be a machine but that a special understanding of machine can provide answers for the questions about man.
A reading of Le Rêve de d’Alembert introduces to Diderot’s view on man and nature. He denies the existence of a nonmaterial soul or mind. He holds a materialistic view but in a sense that is different from contemporary materialist thinkers like La Mettrie or D’Holbach. When Diderot refers to matter, he refers to a sensible matter. Typical distinctions for animate creatures like alive/dead are reduced to distinctions that apply to matter, like active/inactive. But instead of understanding organisms in terms of stable material unity he emphasizes the processes of conjunction and dissolution. Life is a vivid course of events without determined goal. Nevertheless, his explanations of man and human features contain many examples from the fields of instruments, craftsmanship, and technology: He explains thinking in analogy to vibrating strings, imagination in analogy to a self-playing harpsichord, memory in analogy to a self-reading book, the unity of consciousness in analogy to a spider’s web etc. Some of these examples can be seen as machine; others incorporate what can be called mechanism, which structurally applies to machines as well.
There are at least three possible answers to the question about the role of these analogies in Diderot’s writings: They can be interpreted as rhetoric reinforcement of the view that man is not God’s creature but a natural creature. They can be interpreted as an explanation, which reduces the phenomena of life to natural processes that contain, or are, mechanisms. A third interpretation declares the analogies as models with the function to deliver explanation and therefore provide knowledge. The last answer can elucidate his contradictory ascription to the man, that is a machine, and to the man, that is not a machine. “Machine” is no literal attribution, so Diderot does not make an ontological claim. The attribution is rather to be understood epistemologically. The machine is not something one can literally be but something that one can adapt in order to experiment and explain life’s phenomena. In this way Diderot can also give an insight to the creative nature of models in philosophy.