David Hume (1874). “A Treatise on Human Nature: Being an Attempt to Introduce the Experimental Method of Reasoning Into Moral Subjects; and Dialogues Concerning Natural Religion”, p.306
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.14, Hackett Publishing