Sensationism, Knowledge and Probability
Probability and the nature of knowledge
Unlike many of his contemporaries, including d’Alembert, but like Turgot, Condorcet thought that progress was possible in the new moral and political sciences and that it was also possible to reach there the same degree of “certainty” than in the more traditional fields of, for example, physics, chemistry or astronomy (see, for example, the first pages of the 1785 Essai).
This conviction, however, ought to be understood properly. While it implies that the nature of knowledge is basically the same in all fields of inquiry, this nature is such that nowhere is it possible to find propositions that are absolutely certain. This is not only because no science has achieved, or could ever reach, its highest degree of perfection. The reason lies with the nature of knowledge itself. Following Locke and Turgot’s sensationist philosophy, and insisting on the importance of Turgot’s entry “Existence” in the Encyclopedie, Condorcet stressed that any knowledge of the existence and properties of objects comes from our senses and our ability to think about our sensations and combine them. While it is also based on the idea that there exist constant laws for the various observable phenomena, this constancy is only an hypothesis and, by nature, this knowledge can never produce any absolute certainty, whatever the field of inquiry - mathematics included because this hypothesis also concerns the human understanding, and not only external phenomena. It only leads to a more or less strong confidence that these phenomena, in the same circumstances, will happen again in the future.This is the reason why, when Condorcet speaks of “certainty”, he does so only metaphorically to express a great degree of assurance - the word “assurance” is, in his view, more adapted in this context (Condorcet 1785: xvi, 1994a: 523), and a better choice than the ambiguous phrase “certitude morale” (moral certainty). It is also why, in sciences and in everyday life, this assurance is called by Condorcet a probability - founded on past experience and measuring a “motif de croire” (reason to believe).
“The knowledge that we call certain is... nothing else than a knowledge based on a very high probability” (1994a: 602) that in most cases it is meaningless to calculate (Condorcet 1785: xiv). Hence his statement that all propositions “belong to this part of the calculus of probability where one judges the future order of unknown events on the basis of the order of known events” (Condorcet 1994a: 291) and the parallel explicitly made with a classical example in probability theory:The reason to believe that, from ten million white balls and one black, it is not the black one that I will pick up at the first go, is of the same nature as the reason to believe that the sun will not fail rising tomorrow, and these two opinions only differ as to their lower or higher probability. (Condorcet 1785: xi)
However, Condorcet did not follow the sceptical tradition (for further developments, see Rieucau 2003). He believed in the progress and usefulness of knowledge, and he often denounced “the absurdity of absolute scepticism” (Condorcet 1994a: 602). The systematic collectioning of data and the organization of accurate experiences permit an undisputable progress in sciences, and what happened in physics or astronomy will also happen in the new fields concerning society. Politics or political economy, with time, and with the knowledge of human nature based on sensationist philosophy, are liable to approach the same degree of assurance in the truths they establish.