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.