A model should help to direct inquiry and research into public. A concept should be operational-that is, it should refer directly to real-world phenomena that can be observed, measured, and verified. A concept, or a series of interrelated concepts (which we refer to as a model), should suggest relationships in the real world that can be tested and verified. If there is no way to prove or disprove the ideas suggested by a concept, the concept is not really useful in developing a science of politics.