No clear definition of paradigm exists. Three senses have been distinguished as follows:
1. Metaphysical paradigms or metaparadigms, in which paradigms are equated with: a set of beliefs; with a myth; with a successful metaphysical speculation; with a standard; with a new way of seeing; with an organizing principle governing perception itself; with a map; and with something which determines a large area of reality.
2. Sociological paradigms, in which paradigms resemble a universally recognized scientific achievement; a concrete scientific achievement; a set of political institutions; and an accepted judicial decision.
3. Artefact paradigms or construct paradigms, in which paradigm is used: as an actual textbook or classic work; as supplying tools; as actual instrumentation; more linguistically, as a grammatical paradigm; illustratively, as an analogy; and more psychologically, as a gestalt-figure.
From a sociological point of view, a paradigm is a set of scientific habits. By following these, successful problem-solving can go on: thus they may be intellectual, verbal, behavioural, mechanical, technological, or any or all of these, depending on the type of problem to be solved. As such, normal, paradigm-based science constitutes research based upon one or more past scientific achievements that some particular community acknowledges for a time as supplying the foundation for its further practice. Such achievements are: sufficiently unprecedented to attract an enduring group of adherents away from competing modes of scientific activity; and sufficiently open-ended to leave all sorts of problems for the redefined group of practitioners to solve.