David Hume's Treatise of Human Nature, composed before the author was twenty-six years old, was published in 1739 and 1740. Its importance was not generally recognized at the time. Hume, attributing the failure of his Treatise to the manner of its writing rather than the matter it contained, 'cast the firs part of that work anew in the Enquiry Concerning Human Understanding' (1748), and afterwards continued the same process in the second work contained in this volume, the Enquiry concerning the Principles of Morals (1751). Both Enquiries are here reprinted, with an Introduction and Analytical Index by the late L.A. Selby Bigge from the posthumous edition (1777) of Hume's Collected Essays.