In describing his own works of fiction, Graham Greene takes care to distinguish between two kinds of books: his serious novels, like "The Power and the Glory" and "The Heart of the Matter," and what he calls his entertainments, like "Stamboul Train" and "The Confidential Agent." By signaling his intentions so clearly, Greene has saved readers and critics a lot of trouble. Serious literature may be entertaining, but that is hardly its primary function; we may be abashed or uplifted by a book without being amused. When entertainment is the author's avowed purpose, however, different expectations are aroused and different standards of taste apply….

[The] identification of science fiction with entertainment was so complete that if a book used a futuristic setting or scientific gadgetry but was unmistakably "serious"—like Aldous Huxley's "Brave New World" or George Orwell's "1984"—no one except a S.F. fanatic would have dreamed...