The most savage controversies are those about matters as to which there is no good evidence either way. Persecution is used in theology, not in arithmetic, because in arithmetic there is knowledge, but in theology there is only opinion.

It is not enough to have a good mind; the main thing is to use it well. And the greatest minds are capable of the greatest vices as well as the greatest virtues.

It is a truth very certain that, when it is not in our power to determine what is true, we ought to follow what is most probable; and even if we cannot discover which of the alternatives is the more probable, we must nevertheless choose one of them.

To live without philosophizing is in truth the same as keeping the eyes closed without attempting to open them; and the pleasure of waking up is so much more beautiful than that of dreaming, that it must never be desired to have the eyes closed.

It is not what the man of science believes that distinguishes him, but how and why he believes it. His beliefs are tentative, not dogmatic; they are based on evidence, not on authority or intuition.