Translation

“The art of drawing conclusions from experiments and observations consists in evaluating the probabilities, and in judging whether they are large enough, or numerous enough, to amount to proof. This type of calculation is more complicated and more difficult than one thinks; it demands great sagacity and is, in general, beyond the powers of most men. It is upon their errors in this type of calculation that is founded the success of charlatans, sorcerers and alchemists; and, in other times, of magicians, enchanters and, generally, of all those who deceive themselves or attempt to prey on the credulity of the public.

It is above all in medicine that the difficulty of evaluating the probabilities is greater. As the principle of life is, in animals, a force that acts all the time and continually tends to overcome obstacles, and Nature, left to its own resources, cures a large number of maladies; when remedies are employed it is infinitely difficult to determine what is due to Nature and what to the remedy. Thus, for all that most people regard the cure of a disease as a proof of the efficacy of the remedy, in the eyes of a wise man this result is only a probability, more or less large, and this probability cannot be converted into certainty except by a large number of results of the same kind.”

 Translation by IML Donaldson