The real world is much too complicated and complex to analyze as a whole. Therefore, social scientists abstract or simplify real world phenomena by looking at different pieces separately to identify these operational relationships. This abstraction or simplification is theory.
Definitions are the terms and terminology which are to be used in developing the theory.
Words can have many meanings, both inside and outside of the field of investigation. Therefore, a social scientist must state explicitly the meaning of a word as it is to be used in the analysis so that confusion in communication and subsequent development of the logic is avoided. Relationships are a priori conditions which are imposed on the analysis, generally and simply stated in mathematical terms. These mathematical terms are identities, functional relationships, and behavioral relationships. Identities are tautologies or truisms.