Subject headings are the means of conveying the subject content of
h'brary materials to library users. To be more efficient, each subject heading must follow three principles: readers, consistency and specificity. To be able to perform these three principles, the cataloger uses lists of subject headings that are supposed to have performed these
three principles in each one of the subject headings included in them. In subject retrieval of library materials, the principle of consistency plays a major role. This article describes some cases in which the principle of
consistency is unintentionally ignored or is possible to be ignored. Some
solutions are also suggested for each case.