I was a little doubtful about the propriety of going to the Mammoth Cave without a gentleman escort, but if two ladies travel alone they must have the courage of men. ↗
It may be doubtful, at first, whether a person is an enemy or friend. Meat, if not properly digested, becomes poison; But poison, if used rightly, may turn medicinal. ↗
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. ↗