Probabilistic Reason. A controversy of the Enlightenment (Condllac, dAlembert, Diderot)

Abstract

The project aims to reconstruct the theoretical-conceptual shift that, in the middle of the 18th century, led from the idea of demonstration as a procedure that guarantees the certainty of empirical knowledge, to that of hypothesis, conceived either within the framework of a general metaphysics (Leibniz) or within a physiology of understanding (Locke). In the midst of this discussion, what Leibniz calls "probabilistic reason" emerges, possessing an "art of invention", which, amidst the multiplicity of phenomena, finds points of support from which it is possible to launch unprecedented investigations and to unexpected knowledge. The classic example is Copernicus' hypotheses, seen in the 18th century as wrong and overcome, although necessary, retrospectively, to the developments in natural philosophy that culminate with Newton. For reasons worth examining, the application of the calculus of probabilities to physics is contested by d'Alembert, who intends to restrict it to "learned geometry". This position derives from the strict observance of the Newtonian method - which d'Alembert refuses to extend beyond what the most rigorous analogy allows. d'Alembert's restrictions do not only apply to physics, but also apply to medicine, jurisprudence and history - in short, for all empirical knowledge. Diderot rebels against this limitation, and, recovering Leibniz's probabilistic reason (without however accepting its metaphysical implications), uses it as an instrument for extending the domains of physics, which, from now on, will also have to include physiology and chemistry. This movement has important consequences, because, from it, the philosopher conceives a new science, dedicated to the study of living beings, which is ultimately responsible for elucidating the physiological origins (in human reason as the instinct of the species) of calculation itself. of probabilities. This controversy, to date little examined by critics, is a characteristic example of the shift, studied by Kenneth Baker, Ian Hacking and Lorraine Daston, among others, from probability as a mathematical procedure to probability as a philosophical idea. (AU)