Nothing seems to me more doubtful than Aristotle's remark that it is probable the arts and philosophy have several times been discovered and several times lost. ↗
Increasingly, stars are recruited from the ranks of professional models, with the result that today's starlets are better dressed and better groomed than ever before, though it is doubtful if they are better actresses. ↗
Life is like music, it must be composed by ear, feeling and instinct, not by rule. Nevertheless one had better know the rules, for they sometimes guide in doubtful cases, though not often. ↗
That justice should be administered between men, it is necessary that testimonies of fact be alleged; and that witnesses should apprehend themselves greatly obliged to discover the truth, according to their conscience, in dark and doubtful cases. ↗
The tendency of modern scientific teaching is to neglect the great books, to lay far too much stress upon relatively unimportant modern work, and to present masses of detail of doubtful truth and questionable weight in such a way as to obscure principles. ↗