If an event can be produced by a number n of different causes, the probabilities of the existence of these causes, given the event (prises de l'événement), are to each other as the probabilities of the event, given the causes: and the probability of each cause is equal to the probability of the event, given that cause, divided by the sum of all the probabilities of the event, given each of the causes.

Probability theory is nothing but common sense reduced to calculation.

Je n'avais pas besoin de cette hypothèse-là.

Your Highness, I have no need of this hypothesis.

All the effects of Nature are only the mathematical consequences of a small number of immutable laws.

The word 'chance' then expresses only our ignorance of the causes of the phenomena that we observe to occur and to succeed one another in no apparent order. Probability is relative in part to this ignorance, and in part to our knowledge.

His last words, according to De Morgan: Man follows only phantoms.