This paper presents the theory of the categories as developed by Aristotle, Kant and Ranganathan. Subsidies are sought for in order to identify them as fundamental and essential principles for organization of knowledge. Three perspectives are confronted for establishing the differences and similarities in view of the objectives of each categorical system. The conclusion is that Aristotle conceives his principles as fundamental for expressing the ways of being, whereas Kant lists them as ways of thinking. In his turn, Ranganathan formulates the categories as ways of classifying.
Categories; Phylosophycal classification; Faceted classification theory; Organization of knowledge
