502 pp. Harcourt Brace Jovanovich, 1983. THE PHILOSOPHER’S PUPIL, by Iris Murdoch. 576 pp. Viking, 1983. Henry James wrote deprecatingly of novels he deemed to be “baggy monsters”; by way of illustration he cited—a grouping that would not occur to many critics these days—War and Peace, The Three Musketeers, and Thackeray’s The Newcomes. But how, this very assortment of titles begs us to ask, can the novel not be somewhat baggy, as its heritage of roles as historical chronicle, adventure saga, social panorama, and personal confession descends to it and ever more self-consciously complicates and thickens? The masterpieces of this century, as represented by Remembrance of Things Past, Ulysses, and The Magic Mountain, yield nothing in farraginous ambitious bulk to those of the nineteenth cited by James, and the admired American careers of Saul Bellow, Norman Mailer, and Thomas Pynchon show that bagginess, if not esteemed as a virtue in itself, is nevertheless deferred to and indulged, like prankishness in young men, as a sign of vitality.