Henry David Thoreau, Barry Andrews (2005). “True Harvest: Readings from Henry David Thoreau for Every Day of the Year”, p.137, Unitarian Universalist Association of Congregations
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