The Science of Conjecture: Evidence and Probability Before Pascal

by James Franklin

It will have been observed that whenever Nicholas puts forward a new outrageous conclusion, he is careful to say it is only probable. Scattered remarks explain his understanding of probability, the largest being this: “If these reasons are not found absolutely conclusive, nevertheless positing them is probable and more probable than the reasons for the opposite conclusion. To anyone not predisposed more to one side than the other, the degree of probability will appear to predominate (gradus probabilitatis excedens) in these reasons. I speak thus because in the books of others I have seen few reasons for their obscure conclusions that I cannot give probable answers to, and if they say that I deny principles known per se, it is amazing how they express notorious falsehoods. . . . Was it not sufficiently proved above that to say that [the proposition] when blackness succeeds, whiteness no longer exists, is not a principle known by the meaning of its terms, nor through our experience? It is remarkable too how they consider as known per se principles the opposites of which were agreed to by almost everyone before Aristotle, at least the most serious.”