The intention of this book is to lay stress on ideas and tendencies that have to be understood and appreciated, rather than on facts that have to be learned by heart. The book aims at dealing with the matter of authors more than with their lives; consequently it contains few dates. The book pretends no more than to be a general introduction to a very great subject, and it will have fulfilled all that is intended for it if it stimulates those who read it to set about reading for themselves the books of which it treats.