Enquiries concerning human understanding and concerning the principles of morals - David Hume

David Hume's
Treatise of Human Nature, was composed before the author was twenty-six years old, was published in 1739 and 1740. Its importance was not generally recognised at the time. Hume, attributing the failure of his Treatise to the manner of its writing rather than the matter is contained, cast the first 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).