A landmark of Enlightenment thought, Hume's An Enquiry Concerning Human Understanding is accompanied here by two shorter works that shed light on it: A Letter from a Gentleman to His Friend in Edinburgh, Hume's response to those accusing him of atheism, of advocating extreme skepticism, and of undermining the foundations of morality; and his Abstract of A Treatise of Human Nature, which anticipates discussions developed in the Enquiry. In his concise Introduction, Eric Steinberg explores the conditions that led Hume to write the Enquiry and the work's important relationship to Book I of Hume's A Treatise of Human Nature.