Literary texts provide a vein of raw material which is already tested: stories which work and are popular, as well as offering the 'respectability' conferred by the notion of 'literature' in itself, as well as the cache of certain writers. .
The enterprise has commercial aspects too: it is safer to buy the rights to a work than to develop original material. .
Film makers are not known for offering such blunty commerical reasons for making particular adaptations, and, while the writing of the adaptation is itself is a creative undertaking, writers of adaptations rarely announce innovative or bold approaches to their subject matter, tending instead toward caution if not reverence for their 'literary source', and couch their intentions in careful words (McFarlane cites Peter Ustinov, who uses such cautious and respectful phrases as 'selective interpretation' and 'recreate a [certain] mood' etc., p. 7) .
Films that are adaptations are generally popular and successful: according to Maurice Beja the biggest box-office successes tend to be adaptations, and he [ie Beja] also notes that since the Oscars began in 1927-28, more than three quarters of the 'Best Picture' awards have gone to films which are adaptations of novels (Beja, 1979: cited in McFarlane) . .
The Discourse on Adaptation .
On Faithfulness: ideas about 'fidelity' characterise almost every critical evaluation of an adaptation. McFarlane suggests this is because the novel preceded film. Such ideas depend, moreover, upon there being a single 'correct' reading of the novel, to which the filmmaker is 'faithful' or violates. .
There is the idea of a 'literal' translation, and the lesser adaptation, which is true to the 'spirit' of a novel. .
For McFarlane, such ideas are non-starters, despite their prevalence, because they depend upon a co-incidence of one reading (ie 'the meaning') of a novel and another single reading (ie 'meaning') of a film.