Subject Catalogue :
In an alphabetical subject catalogue, entries are made under the name of the specific subjects of documents. Irrespective of their affiliations, specific subject entries are strictly arranged in an alphabetical order. The fundamental rule of entry in an alphabetical specific subject catalogue is to enter a work under its specific subject. For example, a book on 'Roses' will be entered under 'Roses' and not under 'flowers' or 'Botany', which are broader than 'Roses'. Ranganathan defines a specific subject of a document as that division of knowledge whose intension and extension are equal to its thought contents. According to him, the specific subject of 'Teaching chemistry in secondary schools in Delhi' would be 'DELHI, CHEMISTRY, TEACHING 'TECHNIQUE, SECONDARY SCHOOLS, EDUCATION' and not the way it is given in the heading.
In almost every type of library, the predominate requests for documents are by their subjects. Hence extensive provision must be made to give adequate representation to subjects of documents, with a considerable number of cross-references, directing the user to the various aspects of a subject.
While the alphabetical specific subject catalogue provides comparatively easy approach to the catalogue by arranging subjects in alphabetical order, it scatters related subjects. Depending on the incidence of the letter of the alphabet, it disperses entries pertaining to related subjects throughout the catalogue. In fact, one has to refer to a number of subject headings to get a full view of the ramifications of a subject.
In these headings, their alphabetical arrangement scatters the related ones. Agriculture, Apples, Asparagus is subjects group; Aeronautics, Aircraft, Aviation, another group;.Aesthetics and Arts, is still another group; Arithmetics and Astronomy, Arsenic and Atoms, etc., form still other groups. Thus, subject affiliations are totally absent in this type of catalogue. Of course, this difficulty can be overcome by appropriate references.