“It has always been my private conviction that any man who puts his intelligence up against a fish and loses had it coming.”

“...a person who thinks should not try to persuade others to his belief; that is what puts him on the road to a system; on the lamentable road of the "man of conviction"; politicians like to call themselves that; but what is a conviction? It is a thought that has come to a stop, that has congealed, and "the man of conviction" is a man restricted.”

“Wanted, a man who will not lose his individuality in a crowd, a man who has the courage of his convictions, who is not afraid to say "No," though all the world say "Yes.”

“But then with me the horrid doubt always arises whether the convictions of man's mind, which has been developed from the mind of the lower animals, are of any value or at all trustworthy. Would any one trust in the convictions of a monkey's mind, if there are any convictions in such a mind?[To William Graham 3 July 1881]”

“It is the man who all his life has been self-convicted of veracity whose lies find quickest credence.”

“I am a man who, from his youth upwards, has been filled with a profound conviction that the easiest way of life is the best.”