Thomas Clarkson, Ottobah Cugoano (2010). “Thomas Clarkson and Ottobah Cugoano: Essays on the Slavery and Commerce of the Human Species”, p.63, Broadview Press
Joseph Addison, Richard Hurd (1854). “The Works of the Right Honourable Joseph Addison: The Spectator [no. 487-600] The Guardian. The Lover. The present state of the war. The trial and conviction of Count Tariff. The Whig-examiner. The Freeholder [no. 1-30”, p.177
Thomas Jefferson, Henry Augustine Washington (1854). “The Writings of Thomas Jefferson: Being His Autobiography, Correspondence, Reports, Messages, Addresses, and Other Writings, Official and Private : Published by the Order of the Joint Committee of Congress on the Library, from the Original Manuscripts, Deposited in the Department of State”, p.4
David Hume, Eric Steinberg (1992). “An Enquiry Concerning Human Understanding; [with] A Letter from a Gentleman to His Friend in Edinburgh; [and] An Abstract of a Treatise of Human Nature”, p.73, Hackett Publishing