A person who doubts himself is like a man who would enlist in the ranks of his enemies and bear arms agains himself. He makes his failure certain by himself being the first person to be convinced of it.
Doubt, indulged and cherished, is in danger of becoming denial; but if honest, and bent on thorough investigation, it may soon lead to full establishment of the truth.
To have doubted one's own first principles is the mark of a civilized man.
Who never doubted, never half believed. Where doubt is, there truth is - it is her shadow.
Men become civilized, not in proportion to their willingness to believe, but in proportion to their readiness to doubt.
It is evident that skepticism, while it makes no actual change in man, always makes him feel better.
Our doubts are traitors, and make us lose the good we oft might win by fearing to attempt.