The purpose of a good theory is to provide a conceptual framework for viewing and understanding phenomena. From this perspective a theory is either useful or not useful. A theory helps guide and focus attention, identify and define important variables, and postulate the relationships among them. A good theory is not just another 'good idea,' but it is based on empirical data that makes it an adequate map of the territory for the current time. Furthermore, a good theory is never “proven,” which would mean that it holds up under all known conditions--that simply cannot be tested. Instead, scientific method finds it easier to “disprove” or eliminate certain alternate explanations (hypotheses) which means that what is left over is more probable and closer to the “truth.”
Knowing how to evaluate a theory is an important skill in deciding which framework is most appropriate for examining a given situation. Alternately, if you must use a weak theory, at least you will know the precautions for interpreting its data.
The following aspects should be considered in evaluating a theory.
Parsimony
Parsimony is a long-standing criterion for evaluating theories based on the assumption that one of the purposes of a theory is to explain reality by simplification. This means that the explanation is sparing and frugal; it requires assumptions and explanations within generally accepted parameters. If exceptional assumptions are required, the theory is not parsimonious and extensive data and/or rationale would be necessary to justify their use. * Does the theory require a 'leap of faith' in making unconventional assumptions? * If unconventional assumptions are used, are these justified by reason or empirical evidence? * Does it really add to our understanding of a phenomena, or is it just a restatement of something already accounted for adequately by another theory?
Operationality
A good theory should have key terms and concepts that