The survey of the logical bases in Lesson 1 leads to a more definite consideration of the main principles of classification and schedule formation. A close study of natural and artificial classification must be made at this stage. An investigation of the difference between them will stress the importance of the choice of characteristic. It will be emphasised during this lesson that the characteristic selected must be essential to the purpose for which the classification is intended. Botany and zoology have provided notable instances of natural and artificial classification. In studying these schemes notice particularly the process of division, the gradual modulation from Class to Division, Sub-Division, and Section, the Extension of the terms becoming smaller and the Intension greater as the process of division is continued. One fault which can create endless confusion is Cross-Division. To avoid this the terms used in the schedule must be mutually exclusive. The classification of books cannot reach the perfection of a classification of knowledge. The latter is limited only by the limitation of knowledge, but the former by the physical form of books. All bibliographical schemes, however, should be based on the classification of knowledge. Realise clearly the necessity for and the functions of the topic and form classes which form part of every bibliographical scheme. Throughout this lesson it will be seen that classification is governed by the principles laid down in the Five Predicables. If attention has been duly paid to the ground covered in Lessons 1 and 2 no difficulty will in future be experienced with regard to the theory, bases, or principles of classification, but if, on the other hand, any difficulty is felt in answering questions bearing upon these principles, students have devoted insufficient time to their study, and are strongly advised to make good the deficiency before proceeding further. READING LIST. Brown--Library classification. _Chaps. 1 and 2._ Coulson--An outline on the theory of classification. _L.W. Vol. 14, 1911-12, pp. 37-42; 67-70._ Johns--Flowers of the field. _Study introduction._ Richardson--Classification. _Lecture 2._ Savage--Form and alphabetic book classification. _L.A.R. Vol. 9, 1907, pp. 375-383._ Sayers--Canons. _Chaps. 1 and 2._ Sayers--Grammar of classification. _L.A.A. Series, 1912. Principles 1-20._ Sayers--Introduction. _Chaps. 3-5._ QUESTIONS. _1._ What is meant by “cross-division”? _2._ What are essential and accidental characteristics in classification? _3._ The process of division is governed by “difference.” Explain. _4._ Name the difference between philosophical classification and bibliographical classification. _5._ What is the difference between a rigid and a flexible classification? _6._ What is meant by “form” as compared with “subject” in classification? _Lesson 3._ HISTORY. PRINCIPAL SCHEMES. COMPARISONS. SPECIAL CLASSES.