The allegory of Procrustes bed

Discussion on the relation between theory and fact in political science as well as other sciences has been reduced to priority and posteriority of them and thus the pathology of this relation has been ignored. But, this paper by using the allegory of "Procrustes ' bed", firstly, emphasizing the pathology of this relationship. In this pathology, Procrustes ' bed refers to a situation in which researchers only selected or underscored the facts that they are compatible with their theory, but they ignored incompatible facts or modify them in such a way to be consistent with their theory. Secondly with criticizing this approach, see also Popper's falsification model a radical approach and finally argues for Lacatosian model.Thirdly by using of lakatosian method and analysis of the developments of three theories, namely, class theory of Marx, democratic peace theory of Kant and modernization theory, tries to offer a criteria that when we must falsify a theory or modify it. The paper argues when we confront with conflicting facts that challenge belt protective we can modify the theory and when we face with the same situation that hard core of theory was challenged we must falsify that theory. Finally, paper by resorting to cyclical method shows how the death of a theory leads to the birth of another theory.