10. Whatever names are used must be clearly defined. This is the first principle of subject cataloging, whether the arrangement is alphabetical or systematic, that the subject word shall be so clearly defined that there is no mistaking what is to go under it. It is hard to lay too much stress on this matter. It is the Alpha and Omega of subject cataloging of every sort, besides which even uniform names and the question of arrangement are quite secondary. 11. In choosing the names for classes, the most specific should be used. This is a very important aid indeed to clear definition. The only objection is the splitting of kindred subjects--the same idea which leads to the alphabetical classed or systematic catalog. Many cautions are issued warning against being too specific--some well founded, but the danger lies almost wholly in the other direction. There may be a limit but the principle is one of the clearest and most important in the whole matter and even the encyclopedias--even the Britannica itself--are getting further and further away from the old Britannica type. 12. The names of subjects so far as they are identical with author catalog entries should be determined by the same rules as in the author catalog. This is another important aid to uniform names which should be strictly insisted on. 13. The alphabetical subject catalog should have a classed index, as the classed catalog or the shelf list must have an alphabetical index. Note that the index to the new Britannica by its alphabetical index recognizes itself as an alphabetical classed encyclopedia rather than an alphabetical subject encyclopedia. Note also that it has the systematic index--the idea which in the end must be applied to every alphabetical subject catalog and which will be fully served automatically if the names of the classification index are identical with the subject headings and the class number attached to each of the subject catalog headings. 14. Sub-headings and sub-sub-headings should be alphabetically arranged. They should not be systematic or chronological. 15. Sub-headings should be chosen by the same rules and principles as main headings and thus make a duplicate list. There may be practical limits to this but principle is clear. 16. The arrangements of titles under main subject or sub-headings need not be alphabetical. Much is to be said for the chronological order of authorship or publication, but almost the only use for alphabetical arrangement by authors under heading is a poor duplication of author catalog use. It might be a real advantage to break the bad habit of using subject catalog for author purposes and on the other hand, the chronological arrangement of titles in the vast number of cases would save turning all the cards as required in the alphabetical order. Nevertheless the alphabetical is now the common method.