In order that all materials on a particular subject are collocated so that recall may be increased, each subject is represented by only one heading. Synonymous terms and variant forms of the same heading are included as entry vocabulary, i.e., as referred-from terms. In a few instances, duplicate entry headings, i.e., the same heading in different word order or configuration, are made in order to provide access points to significant words imbedded in the heading by bringing them to the filing position.

See also:

3.0 Fundamental principles of Library of Congress Subject Headings