The thoughts that come often unsought, and, as it were, drop into the mind, are commonly the most valuable of any we have. – John Locke, 16 May 1699

Thinking in its lower grades is comparable to paper money, and in its higher forms it is a kind of poetry. – Havelock Ellis, The Dance of Life, 1923

A just thinker will allow full swing to his scepticism. I dip my pen in the blackest ink, because I am not afraid of falling into my inkpot…. We are of different opinions at different hours, but we always may be said to be at heart on the side of truth. – Ralph Waldo Emerson, “Worship,” The Conduct of Life, 1860