Henry David Thoreau (2014). “Citizen Thoreau: Walden, Civil Disobedience, Life Without Principle, Slavery in Massachusetts, A Plea for Captain John Brown”, p.152, Graphic Arts Books
Reinhold Niebuhr (2012). “Man's Nature and His Communities: Essays on the Dynamics and Enigmas of Man's Personal and Social Existence”, p.24, Wipf and Stock Publishers