David Hume, Eric Steinberg (1993). “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.51, Hackett Publishing
David Hume (1779). “An inquiry concerning human understanding. A dissertation on the passions. An inquiry concerning the principles of morals. The natural history of religion”, p.10