The real situation of the medieval Abbasid caliphate was quite different from the ideal of the caliphate which was characterized by the principle of equality of religion and state. In their heyday, the early Abbasid caliphs neglected their religion while pursuing secular political power. But especially after losing their political power at Baghdad, they had sustained titular caliphate with religious authority only. However muslim petty monarchs in local areas showed their oathes of allegiance(bai`a) to their caliph for their legitimacy on kingship based on the traditional islamic recognition that the caliphate should be established by Shari`a. Muslim jurists such as al-Mawardi and al Ghazali had tried to verify the inappropriate relationship between the lines of theory and practice and they established the juristic theory make this relationship continue. The political thought of the medieval muslim jurists had gradually inclined to realism though they had kept their stances on caliphate theory in the issue of state and religion. It is inevitable that they had to compromise with the political reality which had been revealed already, despite their eagerness to keep the practice of caliphate. As a result, the Islamic caliphate could survive while sustaining the dignity and supremacy of Shari`a. However the fall of the Abbasid caliphate was a turning point in the stream of Islamic political thought on the issue of secular political power and religion. The political thought that stressed realism began to have an influence while keeping the political power of state as it was. This political thought was called "siyasa as-shari`a (the politic on Shari`a)" by Ibn Taymiyya which was considered legitimate. He said that the state was still Islamic as long as it was governed by Shari`a. And whoever governs state according to Shari`a and walks through pious religious path could be called Caliph. Ibn Taymiyya considered the Caliph a legitimate ruler as long as the political system was based on realism without affecting the fundamental structure of Islamic principles. An advocate more progressive than Ibn Taymiyya for such a political theory was Ibn Khaldun. He said that the monarch was permissible and agreeable system if it wholly depended on Shari`a. This is the same as the Shari`a politic by Ibn Taymiyya and a copy of his theory. He divided politics into religious politics(siyasa diniya) and rational politics(siyasa `aqliya), the former belonging to Islamic politic and a government based on the Gods law, Shari`a, and the later a political system ruled by secular qanun legitimized by human reason. Religious politic emphases the merit of the caliphate system both in this world and beyond while rational politic stresses the merit of the monarchy in this current world only. To him, Islam, as a religion, is the best regulation and foundation for the political system of state. A uniformed assertion from these Islamic jurists concluded with politics based on the Shari`a. This is not only the backbone of the political thought of medieval Islam, but also became common sense pervading Muslim world today. Indeed it is not flattering that these muslim jurists had created the form of rational political theory which modern Islamic states should be adapted, applied and followed.