Abook is like a single house. it is a mansion of many rooms - rooms on different levels, of different sizes and shapes, with different outlooks, rooms with different functions to perform. these rooms are independent, in part. each has its own structure and interior decoration. but they are not absolutely independent and separate. they are connected by doors and arches, by corridors and stairways. because they are connected, the partial function, which each performs, contributes its share to the usefulness of the whole house. otherwise, the house would not be genuinely livable. the architectural analogy is almost perfect. a good book, like a good house, is an orderly arrangement of parts. each major part has a certain amount of independence. as we shall see, it may have an interior structure of its own. but it must also be connected with the other parts - that is, related to them functionally - for otherwise, it could not contribute its share to the intelligibility of the whole. the most readable book is an architectural achievement on the part of the author. the best books are those that have the most intelligible structure and, i might add, the most apparent. as houses are more or less livable, so books are more or less readable.