“The open road is the school of doubt in which man learns faith in man.”

“One does not learn anything except by believing something, and -- conversely -- if one doubts everything one learns nothing. On the other hand, believing everything uncritically is the road to disaster. The faculty of doubt is essential. But as I have argued, rational doubt always rests on faith and not vice versa. The relationship between the two cannot be reversed. ”

“The man of science has learned to believe in justification, not by faith, but by verification.”

“A faith which does not doubt is a dead faith.”

“I call that mind free, which jealously guards its intellectual rights and powers, which calls no man master, which does not content itself with a passive or hereditary faith, which opens itself to light whencesoever it may come.”

“Man must have just enough faith in himself to have adventures, and just enough doubt of himself to enjoy them.”