Analytical study of relationship between applicability and legality, as two necessary grounds for stability and durability of governments, with regard to their impact on such things as political stability would be necessary. Such being the case, question of the paper follows as: how is the connection between applicability and legality of political governments? The hypothesis runs as: applicability and legality of governments are of such a reciprocal and direct relation that the weakness and strength of each leads to the weakness and strength of the other equally. As is clarified by an analytical and descriptive method in the paper, in spite of reciprocal stability of applicability and legality, applicability of a system would not produce original legality of it. In other word, one may argue that impact of applicability on legality is based on the origin of government`s legality.