"Doubt must be no more than vigilance, otherwise it can become dangerous."

“Where the frontier of science once was is now the centre.”

“Do not commence your exercises in philosophy in those regions where an error can deliver you over to the executioner.”

“There were honest people long before there were Christians and there are, God be praised, still honest people where there are no Christians. It could therefore easily be possible that people are Christians because true Christianity corresponds to what they would have been even if Christianity did not exist.”

“There are very many people who read simply to prevent themselves from thinking.”

“What concerns me alone I only think, what concerns my friends I tell them, what can be of interest to only a limited public I write, and what the world ought to know is printed...”

“There exists a species of transcendental ventriloquism by means of which men can be made to believe that something said on earth comes from Heaven.”