Credulity is a weakness of spirit by which one is inclined to give one’s agreement, whether it be to a proposition or to facts, before having weighed the evidence. It is not to be confused with a lack of piety, belief, or conviction, as it is every day by writers as unfamiliar with our language as they are with philosophy. The impious person speaks with scorn of what he believes in the depths of his heart. The unbeliever denies at first glance the truth he has never examined and does not want to make any effort to examine it seriously. Struck by the apparent absurdity of the thing one assures him of, he does not judge it worthy of careful reflection. The unconvinced examines a thing and, based on the comparison of the thing and the evidence, he believes to have seen from this demonstration of certainty that the thing is as it was told to him. However, the thing as it was reported does not offset his tendency to believe—based on the circumstances of the thing itself or on repeated experiences—either that the thing does not exist at all or that it is otherwise than was reported. There can be doubt about only one possible thing; that one is all the less inclined to believe the passage from the possible to the actual when the proofs of this passage are weaker and when the circumstances surrounding it are more unusual, and when one has a greater number of experiences in which the passage is proven false either in comparable cases or even those cases more usual. In such manner that, if in those cases where a comparable thing is found to be false, there are those cases where it is found to be true, 1,000 to one, then if this relationship were to be just doubled by the combination of circumstances of the thing considered in itself without any regard to the experience, it would be necessary that the proofs of the passage from the possible to the actual be equivalent to at least 1,999. He who has done this calculation under the suppositions involved, and has not found the value of the probability to be equal to 1,999 or less than this quantity will be unconvinced in good faith. He who has not done the calculation at all, and who will have presumed it to be an effort that is and must be as the result of a spirit used to “ferreting out” the truth without entering into a scrupulous discussion of the evidence, will necessarily be an unbeliever. The impious person will have the tongue and the talk of the unbeliever, and in his spirit a contrary presumption. Hence, the unconvinced deserves to be instructed and the unbeliever to be exhorted; the impious alone is without excuse. The person lacking in piety is in no way averse to credulity , that is, easy belief. An idolater who believes in his idol and breaks it when it does not answer his prayers is impious; a Catholic who comes to the communion table in an inappropriate frame of mind is impious. A Muslim, in whose eyes the various articles of his belief are just so many dreams not worthy to occupy his reflections, is an unbeliever. The Protestant who, on impartial examination, ends up having grave doubts about the preference he is giving to his sect, is a person lacking in conviction. For the others, since it is a matter of moral questions here, it could well happen that even if there were 2,000 to one that a given thing is, nevertheless it would not be. The unconvinced person can therefore reasonably assume the truth exists where there is none: it is even more easy for the unbeliever to make an error. But it is not at all a matter of what is or what is not, it is a question of what it is that appears to us. It is with ourselves that it is important to settle matters, and when we are of good faith the truth will not elude us. There is the same danger of rejecting everything and accepting everything indiscriminately. This is the case of credulity, the vice most susceptible to lying.