John Stuart Mill (2008). “Utilitarianism and On Liberty: Including 'Essay on Bentham' and Selections from the Writings of Jeremy Bentham and John Austin”, p.67, John Wiley & Sons
Neil Armstrong's letter to the children of Troy, Michigan on the opening of its Public Library (1971), as quoted in "Why Libraries Matter: Letters to the Children of Troy, Michigan (From 1971)" by Lucas Reilly on Mental Floss, July 3, 2012.