ÒIn field after field,
theories of composite authorship, earlier
versions, different strata, have been discarded. The kind of analysis which was once thought to have been
the particular duty of literary criticism is now
markedly out of fashion. The assumption today is
more and more in favour of single authorship,
unless there is clear external evidence to the contrary.Ó
– Helen Gardner, The
Business of Criticism (Oxford, 1959), p 97.