The paradigm concept is the idea that in any field at any given time there is a set of assumptions shared by most of those working in the field. The paradigm defines the field and shapes the rules of the game. It determines what gets studied, the methods, and how the findings are interpreted. It defines the needs addressed, who is served, and how the services.
A paradigm is entrenched and self-sustaining, and provides continuity and stability. Its tenets are defended and change is resisted. A paradigm becomes more complex and encompassing, but does not evolve.
Paradigms change through radical and sudden shifts. These occur when new discoveries, knowledge, or concepts arise which cannot be rejected or assimilated.