In general, scientific theories are developed in order to predict or to explain phenomena:
Prediction is an operation that makes it possible to foresee results of experiments not yet performed, thereby reducing the apparent complexity of the perceivable world [Kampis, 1991].
Explanation is an answer to a `why?' question. If is a presumed empirical fact, then the question ``why is it the case that ?'' is an explanation-seeking question. If is a hypothesis, then the question ``why will occur?'' is a reason-seeking question [Hempel, 1965].