The Eugene Vinaver edition, based on the document formerly known as the Winchester Manuscript (now British Library Additional MS 59678) gave scholars their most important improvement in their idea of Malory's text since William Caxton printed the first edition in 1485.  The discovery of this manuscript in 1938 challenged all previous Malory scholarship.  To read the story of how Walter Oakeshott discovered the manuscript, click here.  To see images of every page in Caxton's first and second editions, go to this British Library web site.  All free texts of Malory which you can read online will be based on Caxton's edition, and will be missing several important parts of the text that the printer apparently removed before printing (e.g., the prison explicits).  Caxton worked in an era in which printers typically took greater liberties than a modern editor when preparing an edition for the press, and given the subject matter's political importance to the Yorkist-Lancastrian succession dispute (Wars of the Roses), he had ample motives for wanting Malory's version of the Arthurian past to sell to English readers.  (Also, it was a huge, expensive book to print, so he stood to lose a lot of money if it did not!)  For this reason, you cannot rely on Caxton's Malory for your primary reading of the text, but Caxton's Malory is still considered one possible form of the text for analysis.  Most scholars choose to study Vinaver's, which is available only in print because it is still under copyright.  All page references on my web site are to Vinaver's Oxford University Press paperback edition (1977), which is based on the three-volume hardcover revised edition (1967).  (Since then, P.J.C. Field, an eminent Medievalist and Malory scholar, undertook a third edition based on Vinaver's second, to correct errors detected by scholars since the 1967 edition came out, but usually the changes are relatively minor.)

        Nevertheless, Caxton's edition is important because he is our first recorded Medieval reader of Malory, as reflected in the way he arranged and changed the text he found in the manuscript given him in about 1484, a close cousin of the Winchester Manuscript which Vinaver used for his source.  This makes him ideal for testing "Reader-Response" insights about how Malory's narrative might play to and with contemporary readers' expectations (via snares, equivocations, partial answers, and disclosures), and  Debate still rages over accepting Vinaver's radical division of the work into 8 individual "works" with no necessary relationship to each other, so Caxton's reading of Malory as intending a single unified "work" has great value for us.  You can refer to Caxton's readings of passages to challenge Vinaver's and to support your own.

        Note that students of some modern poets like Wordsworth and Auden also have a similar difficulty, because poets sometimes publish significantly different versions of early work at later points in their careers.  Most students find it difficult to abandon the myth of the stability and transparency of the primary source text, because it's hard enough to interpret the complex information from even one reliable text.  But once you get used to using your introduction to establish what text you will analyze and why you have chosen it instead of the others available, you will see it grants you significant interpretive advantages.  You no longer have to deal with literature as a mass-produced, transcendentally existing commodity, but rather literature resides in an unique manuscript, a material historical artifact whose construction and provenance (history) can give us important clues about the work's meaning.