Mechanisms of life in the seventeenth century: Borelli, Perrault, Régis

In Descartes's reformulation of natural philosophy, two aspects of what came to be known as the mechanical philosophy were intimately joined: mechanism as an ontology of nature, according to which all natural things had only 'mechanical' properties; and mechanism as a method of explanation. One could, and many philosophers did, adopt mechanism as a method of explanation without adopting a mechanistic ontology. I examine two successors of Descartes who did just that, and one who did not. Giovanni Alfonso Borelli in his De motu animalium (1680) and Charles Perrault in his Mécanique de animaux (1680-1688, Vol. 3) propose and argue for a variety of mechanical accounts of the operations of animals, in particular of their muscles. They reject, however, the Cartesian reduction of animal souls to mechanical forces; the principle of animal motion for them remains a non-mechanical soul. Pierre Sylvain Régis in his Cours entier de philosophie (1690, 1691) follows Descartes in taking the 'physical cause' of motion in animals to be the fermentation of blood in the heart, and thus denies animal souls any role in his physiology. That he can do so while taking over, sometimes word for word, Perrault's accounts of animal motion shows that mechanistic explanation and mechanistic ontology could easily part company.