It resembles with the historical method, but is more general than the latter. It was first employed by Aristotle, who was said to have compared 150 constitutions in order to State general principles underlying them. In modem times it was used by Montesquieu, Maine, De Tocqueville, Bryce and others. The comparative Method is, first of all, based on the general scientific principle that similar causes produce similar results. Comparative Method requires accumulation of six logical processes, arrangement, classification, coordination, elimination, and deduction. By these processes we sift out common causes and consequences.
On this basis we can State the law that if the common cause is found in any situation afterwards, it will be followed by the same consequence. For instance, if we compare two democratic States and find one prosperous and the other not, and also find that the prosperous one follows a protectionist policy, we are justified in concluding that protectionist policy produces prosperity.
The Comparative Method has been much applied in framing new constitutions in modem times. For instance, when the Constituent Assembly of Pakistan was drafting the proposed Constitution few Pakistan in 1951-56, it undertook a comparative study of the existing Constitutions of Western Europe, America and of certain Muslim countries, and was guided in its task of framing 1956 Constitution by the conclusions of this comparative study.
The Comparative Method must, however, be used with great care. It has certain defects. It is based on that facile assumption that the same cause in different circumstances will produce the same result. Ih comparing political institutions with a view to find out the general principles underlying them, we must take into account the diversity of conditions and circumstances. Superficial resemblance must not make us believe that two States are identical in basic principles as well.
Differences of economic and social conditions, of temperament and traditions, moral and legal standards, etc., determine die basic features of a polity. For instance, no comparative study can conclusively prove that the parliamentary system of government will produce the same results in Pakistan as it did in England. In fact the makers of the Pakistan Constitution of 1956 set up the Parliamentary system in our country on English model, but it soon failed to work. It was due to the differences between Pakistani and British political cultures. Hence, three precautions are necessary in a comparative study: to avoid superficial resemblance, to assemble all the relevant facts of the problem under consideration and to make proper allowance for diversity of conditions and customs.