The answer in the second case will be clear to any one who has followed our argument with attention. The intellectual and religious outlook was so similar in both religions and the problem requiring solution so far identical that nothing existed to impede the adoption of ideas originally Christian which had been developed in the East. The fact that the West could accept philosophical and theological ideas from Islam and that an actual interchange of thought could proceed in this direction, is the best of proofs for the soundness of our argument that the roots of Muhammedanism are to be sought in Christianity. Islam was able to borrow from Christianity for the reason that Muhammed's ideas were derived from that source: similarly Christianity was able to turn Arab thought to its own purposes because that thought was founded upon Christian principles. The sources of both religions lie in the East and in Oriental thought. No less is true of Judaism, a scholastic system which was excellently adapted by its international character, to become a medium of communication between Christianity and Muhammedanism during those centuries. In this connection special mention must be made of the Spanish Jews; to their work, not only as transmitting but also as originating ideas a bare reference must here suffice. But of greater importance was the direct exchange of thought, which proceeded through literary channels, by means of translations, especially by word of mouth among the Christians and Muhammedans who were living together in Southern Italy, Sicily, and Spain, and by commercial intercourse.