Although for the purpose of this article English literature is treated as being confined to writings in English by natives or inhabitants of the British Isles, it is to a certain extent the case that literature-and this is particularly true of the literature written in English--knows no frontiers. Thus, English literature can be regarded as a cultural whole of which the mainstream literatures of the Unit- ed States, Australia, New Zealand, and Canada and important elements in the literatures of other commonwealth countries are parts. It can be argued that no single English novel attains the universality of the Russian writer Leo Tolstoy's War and Peace. Yet in the Middle Ages the Old English literature was influenced and gradually changed by the Latin and French writings, eminently foreign in origin, in which the churchmen and the Norman (诺曼) conquerors expressed themselves. From this combination emerged a flexible and subtle linguistic instrument exploited by Geoffrey Chaucer (乔叟) and brought to supreme application by William Shakespeare.