George Berkeley (1752). “Alciphron: Or, The Minute Philosopher. In Seven Dialogues Containing an Apology for the Christian Religion Against Those who are Called Free-thinkers”, p.112
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.10, Hackett Publishing
Ralph Waldo Emerson, Robert Ernest Spiller, Alfred Riggs Ferguson, Joseph Slater, Jean Ferguson Carr (1971). “The Collected Works of Ralph Waldo Emerson: Nature, addresses, and lectures”, p.68, Harvard University Press