The OLD DIV(inity) classification was used for material cataloged in this library before 1971.
The OLD DIV classification begins with the letters A, C-Z (for secular subjects), or the numbers 10-999 (for religious / theological subjects). (The numbers are theoretically part of the OLD DIV 'B' classification; however, 'B' was never included as part of the call number because it was assumed that most of the collection would be in 'B').
Some OLD DIV titles have author designations or 'Cutter numbers' (after Charles Ammi Cutter) similar to those found in the LC collection. Other OLD DIV titles have only this 'class mark' and are supposed to be arranged on the shelves by author. These sections of the stacks are, understandably, sometimes out of order. If you are looking for an item with such a number, you may need to browse through the shelves with works of the same number.
The OLD DIV(inity) classification was established by the Rev. Owen Gates, the first librarian of the joint Harvard and Andover Library, and revised by other librarians before 1971. Like the Library of Congress classification scheme, it was based on and influenced by the 'Cutter Expansive Classification' (you can see their similarity if you compare LC and the OLD DIV alphabetic classification).
Contrary to popular opinion, the OLD DIV classification is not the Dewey Decimal classification.
OLD DIV(inity) Alphabetic Classification
OLD DIV A General works, encyclopedias, etc.
OLD DIV C Secular biography
OLD DIV D Historiography, Philosophy of history
OLD DIV E Secular history
OLD DIV H Social sciences (General works)
OLD DIV I Sociology
OLD DIV J Education
OLD DIV K Political science
OLD DIV L Law, Sex, Marriage, etc.
OLD DIV M Secular music
OLD DIV N Art
OLD DIV Q Natural science
OLD DIV T Medicine
OLD DIV X Language, dictionaries, grammars, etc.
OLD DIV Y Literature
OLD DIV Z Library science, bibliography
OLD DIV(inity) Number Classification
OLD DIV 10-29 Philosophy
OLD DIV 31-49 Psychology
OLD DIV 51 Ethics
OLD DIV 101-199 Religion (comparative religion, world religions except for Judaism and Christianity)
OLD DIV 201-299 Judaism, other Semitic religions
OLD DIV 301-349 Bible
OLD DIV 350-499 Hebrew Bible/Old Testament
OLD DIV 501-598 New Testament
OLD DIV 601-610 Christian writers, theologians, etc.
OLD DIV 611-689 Christian theology
OLD DIV 691-699 Christian ethics
OLD DIV 701-719 Christian ecclesiastical theology
OLD DIV 720-799 Christian liturgy/ritual
OLD DIV 801-811 Christian pastoral theology
OLD DIV 812-817 Christian missions
OLD DIV 818-828 Christian education
OLD DIV 829-897 Christian homiletics and sermons
OLD DIV 901-911 Christian church records
OLD DIV 912-918 Christian church history by periods
OLD DIV 919 Christian church history by places
OLD DIV 921-928 Eastern/Orthodox churches
OLD DIV 931-940 Roman Catholic Church
OLD DIV 941-943 Protestant churches
OLD DIV 944-946 Christian monasticism, martyrologies
OLD DIV 948-949 Church councils
OLD DIV 999 Christian biography