Categories, Facets and Isolates:
A solitary, unattached idea, which cannot be further, subdivided, and by itself it cannot form a subject, is called an isolate. For example, the terms wheat, child, India are isolates as by themselves they are vague. These have meanings only in the context of a main class. For example, wheat diseases, child psychology or India: history have meanings. An isolate is the ultimate division of knowledge. Going back a little, Ranganathan defines a compound subject as a basic: subject forms a compound subject having one or more isolates, An isolate is the context of a basic subject forms a compound subject and a Basic Subject is a basic subject without an isolate idea.
Isolates are grouped in what are called facets on the basis of-common characteristics. A facet is thus a totality of isolates obtained on the basis of a single train of characteristics of a given entity. As a matter of fact, Ranganathan defined facet as "A generic term used to denote any component- be it a basic subject or an isolate - of a compound subject, and also its respective ranked forms, terms, and members". We may speak of Basic Facet, Isolate Facet, Geographical Fact,Language Facet, Educational Facet Property Facet, Organ Facet, Cultivar Facet, etc.
The totality of the facets having a common characteristic form a category. For example,-in library science all the facets pertaining to the kinds of library, j-.e., academic, public, special, form a category named personality category, in this 6ase. Yet; another "category -is the library activities, i.e., acquisition, processing, servibes, preservation, called energy category in this case. A category is a highly, generalized division of knowledge. Ranganathan postulates that a subject is constituted of at the most ' five fundamental categories, namely, Personality, Matter, Energy, Space and Time. In other words all the concepts of the universe of knowledge belong to five and only five fundamental categories