5. The prime object of a library catalog or directory to books for use resolves itself into a matter of the economy of time and of attention. Where there are only two or three books in a man's library there is obviously little need of catalog. As soon as there are many the guide book is needed. Whether, therefore, the catalog is author or subject, the controlling thought in its making is the economy of attention of the user. 6. The alphabetic order is on the whole the quickest reference order. The economic solution for these two needs proves, therefore, to be, the two alphabetical catalogs (1) the author and title catalog, (2) the alphabetical subject catalog. Title catalogs and the like are simply supplementary practical devices to aid inexperienced or forgetful readers. The author and title catalog is distinguished from the author and catch-word catalog by the entry of anonymous titles under the first word rather than under the most significant word. 6b. Following a natural evolution, the systematic library catalog and the alphabetical classed catalog are practically extinct species, overwhelmed in the struggle for existence by the alphabetical subject catalog's quick and ready reference. This economy is, to be sure, effected for the average use, at a very great expense to the use of a good many readers who wish to consider all related aspects of a topic, but with the growing habit of classification of libraries, there is in fact a handy substitute, for these readers, in the classification, its index, and the shelf list. The alphabet subject catalog has thus become the recognized sole form of subject catalog for users in general. 7. The nature and origin of the alphabetical subject catalog is the same as that of the alphabetical encyclopedia, the alphabetical index to books and alphabetical index to a system of classification. Its rules and applications may, therefore, be guided by experience and practice in these three fields as well as direct experience in the alphabetical subject catalog. 8. Habit being a chief factor in quick reference, it is important that the name of the subject should be that of common usage. By this is not meant necessarily the use of the common people, but the form generally used in book indexes, encyclopaedias, and library classifications. It is greatly to be desired that all encyclopedias, classifications, indexes and alphabetical subject catalogs should use just the same terms--the same form among synonyms, the same practice as to singular or plural, adjectives or substantive entry. 9. At least the names of the subjects in the alphabetical subject catalog should be identical with those of the alphabetical index to the systematic catalog if there is any or the classification of its own library.