Let us now proceed and consider later medieval Christian philosophy in order to examine the extent to which Islamic and Christian philosophers have influenced each other. St. Thomas Aquinas presents a perfect picture of a philosopher whose works are not only influenced by Greek philosophy but also by Islamic philosophy. He learned much from al Farabi's logical treatise and borrowed much of Ibn Sina's ontological scheme. His Summa Theologica bears the influence and the impact of Islamic philosophy upon him, although he expressed repeatedly that he detested Islam as a religion. With the influence of Islamic philosophical thought on much of Aquinas's writings, the picture that emerges is that of a person who, despite vast religious differences with Islam nevertheless shared with it a sacred universe and a common language. Thus, he was able to use the findings of such a religious adversary as Ibn Sina. To this equation, one can even add Moses Maimonides, who shared this sacred worldview and language, as his writings bear testament.
A brief glance at the history of medieval intellectual thought reveals an ecumenical dialogue between East and West that communicated with each other because they shared a common language. It is precisely this common language that allowed two distinct traditions to communicate with one another.
The common sacred language and universe of the Islamic-Christian religious universe broke down following the end of the medieval period in Europe. With the Reformation and the Renaissance, Europe marginalized religion and thereby determined the social direction toward which Europe would begin its intellectual journey. With the Renaissance, Europe ended its common language with Islam and thereafter made a concerted effort to shift the focus of its civilization from theos to anthropos. This shift was a return to the Greek intellectual world in which man is the only measure of things, and thus the West began to criticize itself through Greek eyes. What is noteworthy and apparent in this deconstructionist effort of the Enlightenment is the reliance on the humanistic secularism of the Greeks. This time, however, it was not used to construct a dialogue between Greek thought and the Christian worldview, but rather to "deconstruct," "demythologize," "de-mystify," and, finally, to destroy Christianity.
Following the Renaissance, the West chose a different intellectual paradigm. It also changed the language with which it had communicated with other civilizations as well as with its own past. The changing of a common language between this secular and newly converted West and other civilizations that had retained God as the center of its universe resulted in the end of communication. Perhaps nowhere was the impact of this profound change more drastic than on Islamic civilization, which remained staunchly theocentric. It is a symbolic coincidence that René Descartes, the father of modern Western philosophy who introduced the notion of "doubting anything that can be doubted," is a contemporary of the grand metaphysician of Islam, Sadr al Din Shirazi (Mulla Sadra), who advocated the attainment of certainty through intellectual intuition.
It would not be unreasonable to say that since the Renaissance, Islam and the West have found no common language with which to communicate. Even throughout the medieval period, which often symbolizes the conflicts between Islam and Christianity, a traditional Muslim and a Christian would have found very little about which to disagree, particularly regarding moral rights and wrongs. In the post-Renaissance era, however, Muslims and Westerners find very little to agree upon, a condition that has produced a great deal of tension, as noted by S. Huntington in his article "The Clash of Civilizations.
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This brings us to a problem that we face in our contemporary attempts to have an ecumenical dialogue with the West, in general, and the Christian West, in particular. The West has a greater degree of tolerance for accepting "the other" precisely because it has undergone the experiences of Reformation and Renaissance. Such a metamorphosis has made the West value-free and therefore more accepting of the new "isms" than the Islamic Weltanschaaung, which is divided strictly along the sacred and the profane. How can the Islamic world, which has gone in a different direction during the last four centuries, communicate with the modern West, which has abandoned the sacred and thereby eliminated that which was held in common? In fact, the modern secular West is not any more capable of having a discourse with its own fundamentalists and defenders of God than it is of having a discourse with Muslims.
