Some of the fundamental principles may seem more like rules than principles at first sight but it is believed that they are all well principled. However, it is not pretended that they are all the principles in sight; quite the contrary, there is quite a pocket-full of these left each with the memorandum of some principle, big or little, and there are but twenty-one here enumerated. This being a discussion rather than a systematic paper properly refers to matters of recent personal experience. Since the first page of the new subject index contains subjects down to the name "Absolute," there has been drawn a synopsis of all the subject headings used by the A. L. A., Library of Congress, Harvard, Sydney, Princeton and the indexes of the Expansive Classification and Decimal Classification. This will illustrate the variety of usages which have to be dealt with in attempting to systematize this matter so as to get uniformity and may be regarded as illustrations of the principles enumerated. 1. A catalog is a name list of concrete or specific objects as distinguished from classes of objects; a list of plants in a botanical garden, of mineral specimens in a museum or books in a library, but a list of kinds of plants, minerals or books apart from concrete specimens is not. In the case of books such a list is a bibliography. The book catalog is a directory or guide book to certain concrete books, the bibliography is a list of books in the abstract, applying equally whether its books exist in one place or another, or even if they no longer exist at all. 2. A library catalog is a directory or guide book to books for use. The immediate object to publishers, new book dealers, book auctioneers or antiquarians is sale, the object to the librarian is use. This difference affects both the form of the catalog and the description of the books. 3. Library catalogs in turn may be distinguished into catalogs for the administration (which include chiefly accession catalog and the shelf list) and those for direct use of readers (which include author, subject, title, imprint, etc., catalogs)--the special use in every case modifying the form of the catalog. 4. Catalogs for readers differ according to the two needs of readers which the catalogs try to meet. These needs are (1) To find a given book; (2) to find a book or group of books of a given character. It is not quite exact to say under this second head, that the object is to find information on a given subject or topic, for it may be that the object is to find special forms such as incunabula or Venetian imprints, association books, fiction, poetry, drama, essays, orations, ballads, encyclopedias, dictionaries, periodicals, classes of rarities, books on vellum, etc.