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 .