It's known Hume's Treatise on human nature wasn't very successful when first released and then he reworked the Book 1 of it in An enquiry concerning human understanding, but where can we see a good explanation for this happening in his own words and what are some good sources to understand his movement from one book to another?
Also, how An abstract of a book lately published: entitled a treatise of human nature is related to the Enquiry?
Welcome, JorgeAmVF
It would be a mega-task to work out the full relation of Treatise I to EHU - and the outcome certainly not beyond challenge. The following extract from an article by Phillip Cummins throws some light, however. Four main point are involved :
... In closing may I suggest that [1 - GLT] Hume disowned the Treatise primarily because it provided handles for attacks on him and because he came to abhor its brash and dogmatic style. This is not, in itself, an explanation of the differences between the Treatise and Enquiry. [2 - GLT] What seems likely is that the latter was designed to carry forward more fully and more successfully the program of the Abstract of a Treatise of Human Nature. Hume by no means repudiated the Treatise in the Abstract, but he did acknowledge that its length and abstractness made it difficult to comprehend. [4 - GLT]To remedy this-that is, to make his philosophical system more accessible-he decided to limit his discussion of the Treatise to one central and important topic, causal inference, and to provide only hints regarding "particular passages which seemed to me curious and remarkable. Now the Enquiry develops along similar lines. Hume concentrated on causal inference. After providing the needed introductory material (Sections One through Three), he proceeds to offer his analysis of such inferences (Sections Four through Seven) and then apply it to a number of related topics (Sections Eight through Eleven). Section Twelve provides hints regarding curious and remarkable doctrines. There are a number of links connecting the Abstract and Enquiry - for example, the introduction of Adam with his faculties perfected and the introduction of the billiard balls, so there is some basis for the suggestion that the former was the model for the latter. This hypothesis, at least, has the advantage of not requiring the claim that Hume repudiated doctrines of the Treatise which happen to be omitted from the Enquiry.** ( Phillip D. Cummins, 'Hume's Disavowal of the Treatise', The Philosophical Review, Vol. 82, No. 3 (Jul., 1973), pp. 371-379: 378-9.)
Let's descend to detail just for illustrative purposes to EHU, Section 12:
Hume, of course, did not jam all of Part Four of Book One of the Treatise into Section Twelve. They do, however, have a common theme: the uses and abuses of skepticism. Furthermore, the uses to which Hume put at least some of the doctrines developed in detail in the Treatise conflict with ... [the] claim [sometimes made] that by the time of the composition of the Enquiry Hume had repudiated metaphysics. In Part Two of Section Twelve, Hume argued that mathematicians assist skeptical attempts to turn reason against herself with their demonstrations that finite magnitudes and durations consist of an infinite number of parts. He added, in a footnote, that such an absurdity can be avoided if one holds, "that there is no such things as abstract or general ideas," and insisted, in another footnote, that there are "parts of extension, which cannot be divided or lessened, either by the eye or imagination." Both claims were defended at length in Book One, Part Two, of the Treatise. In Part One of Section Twelve, Hume summarized his attack on the primary and secondary qualities distinction in Section Four, Part Four, Book One, of the Treatise. That attack was based upon the doctrine of colored and tangible points expounded in opposition to the doctrine of infinite divisibility. Hume also retained in Section Twelve the devastating critique of both natural and philosophical beliefs in external objects which was first developed in Section Two of Part Four of Book One. He merely omitted detailed causal explanations of those beliefs. The metaphysical doctrines of the Treatise were not repudiated; rather, the detailed psychological arguments concerning the causes of beliefs were dropped. Strange behavior for one fleeing the corruption of metaphysics. (Cummins: 377-8.)
A light illustration of the connection : There are a number of links connecting the Abstract and Enquiry - for example, the introduction of Adam with his faculties perfected and the introduction of the billiard balls, so there is some basis for the suggestion that the former was the model for the latter.
But more in detail :
The title page of the Abstract of the Treatise tells us that in it "The Chief Argument of that Book is farther illustrated and explained". The contents of the Abstract show the "chief argument" to be the theory of causal inference presented in the central sections of Part III of Book I of the Treatise. Thus we may know what Hume himself regarded as being of basic significance in his new philosophy. (Ralph W. Church: Review of An Abstract of a Treatise of Human Nature by David Hume, J. M. Keynes and P. Sraffa, The Philosophical Review, Vol. 48, No. 6 (Nov., 1939), pp. 643-644: 644.)
It is a small step from recognising the Abstract as pointing out the matters of principal importance in T Bk I to seeing EHU as setting out just those matters more concisely, more precisely, and altogether more accessibly than the argument and exposition of the Treatise had managed to do.
