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.