One of the funniest chapters of Vyronis' book tells how the Byzantine intelligentsia coped with the loss of the empire. The Middle Ages were the golden age of religion; everything was understood in terms of God and scripture, all matters big and small were referred to the local priest or bishop, which would use their theological training to explain to the flock how anything, from the local disease which decimated a village's livestock, to an earthquake that devastated a whole area, it was all God's will, chastening the people for their sins.
Well if an earthquake is a proof of God's wrath, the Turkish invasion surely meant God was really really pissed. How did the theologians deal with that? Muslims were as likely as Christians, if not more so, to credit God for their victories, and they surely seemed to have the upper hand in the God's with us business. So what was a Constantinople intellectual supposed to do? Accept God's message and convert? Hell no. People don't spend decades analysing the most intricate minutiae about the relation of the Father and the Son, the double nature of Christ, or the surface area of angels and pins, just to throw it all away and get in the business of hadith reciting. There's already enough competition there already anyway.
So Christian intellectuals chose to fight Islam in the realm of ideas. One funny thing about Muslims that is little acknowledged today, is that the people really think their religion is true, and do enjoy talking and arguing about it. The 11th century also was a time of great intellectual activity in the Muslim world, producing Avicenna and Al Gazhali among others. These were an upbeat people confident of their power and brains. And they sought out the Christians to convince them of the error of their ways.
Yet the Muslims weren't still on the Christians league. For all the Islamic Golden Age and its output, the fact remains that Islam is a pretty retarded religion. The Koran is a lame, dumb book, poorly written, and the hadith are just a bunch of ad hoc bylaws probably made up on the spot during the centuries. Thus the Christians, who had a millennia of training about religious disputation (mainly against their own Christian heretics), when given the chance to express their views were bold to surprising extent:
We are told by a Muslim chronicle, for example, that the Greek beglerbeg of the Seljuk sultan ‘Izz al-Din took a perverse stand against the Muslim emirs because of his Christian fanaticism and attempted to surround the sultan with his own men in order to remove him from the influence of his Muslim advisers. While at Filubad, the sultan’s pleasure palace, the Christian official is reported to have taunted the Muslim Badi al-Din with the remark, “I understand that your caliph has been killed” (in reference to the fall of Baghdad to the Mongols). The Muslim promptly replied that this should not seem strange to one in whose religion God (Christ) was “hanged” !
Touché. Still Christians generally were the better debaters, which of course pissed the boss:
Further incidentals in regard to this polemic that transpired between Christian priests and Muslim religious men emerge from the accounts of Eflaki and the synodal documents of the fourteenth century. Matthew, the fourteenth-century metropolitan of Ephesus, complains that his religious discussions with the Muslims of Ephesus aroused the animosity of the Turks and resulted in his being stoned.
What did they get so reeled about? I quote Vyronis again:
when Palamas engaged in controversy with the Danishmend of Nicaea, the latter put to his Christian opponent a much repeated question. Since Muslims honor all the prophets (Christ included) and the four books that have come down from God, why do the Christians not accept Muhammad and the Koran? Palamas, and the other Greek polemicists as well, inevitably replied that nothing can be accepted without proof or witnesses, and this proof can be of two categories, proof from Muhammad’s works and proof from reliable individuals, both were lacking. Muhammad did not resurrect the dead, heal the sick, or halt the winds and waves, as Christ had. And the few miracles that the Muslims alleged were not satisfactorily witnessed. Who saw Gabriel convey God’s revelation to Muhammad as the latter slept? Even if the angel had actually appeared to Muhammad with the revelation of God, it was the angel rather than Muhammad who was the real prophet. And was it not strange that though the Muslims required “twelve” witnesses to the taking of a legal wife, yet they accepted Muhammad’s miraculous leap to heaven on the sole testimony of Fatima?
the Christians were most frequently defending their religion against the Muslim charges of polytheism. By the mystical doctrine of the Trinity, it was charged, the Christians had given God associates. And if they could associate two with God, why not three, four, or more? Moreover, the argument continued, Christ was a man and not divine, for how could God fit into and be born from the womb of woman? What does the incarnation avail Christians? Could not God have saved man in some other fashion? The Byzantine replies to these attacks were a curious mixture of clever philological arguments and propositions attained as a result of faulty translation from the Arabic of the Koran. First, the prophets who spoke of Christ referred to Him as the Son of God, as God, and as One who would be incarnate. Second, the Muslims themselves accepted the fact that Jesus is the λογος (word) and πνευμα (breath) of God and that these are in God. For to argue the contrary is to say that God is αλογος and απνους (thoughtless and breathless), and this would reduce God to dead matter. Therefore the spirit and the logos have always been with God. And Christ, as being born of the Virgin, is also man, as the prophets prophesied. How his birth came about is a mystery, but to deny God’s incarnation as an impossibility is to admit that God is not omnipotent.
It wasn't all theology. Islamic morality was attacked too:
The unrestrained hedonism of Muslim life was, to the Christians, manifested in a variety of ways. Not only were “sodomic” practices allowed and the defloration of virgins and the custom of prostitution, wives were easily and frequently divorced. The immorality in such “easy” divorce was compounded, in the eyes of the Christians, by the fact that should the husband wish to remarry the wife, he could not do so until she had been taken in wedlock by another man. Thus the law of divorce and remarriage involved further and “legalized” adultery. This was not lo be wondered at, for Muhammad himself was a fornicator who used aphrodisiac, a pseudo- prophet who manufactured a revelation ordering his companion Zayd to relinquish his beautiful wife so that Muhammad could marry her. The very hedonistic and physical character of Muhammad’s teaching was sufficient to indicate to Byzantines that it was a false teaching.
And some surprisingly modern arguments:
if a man is to be given many women in paradise because of his good life on earth, then it follows that women should enjoy the same rewards because man and woman are of one nature and they shall be judged in the same manner. Therefore, according to the foolish preaching of Muhammad, it follows that a woman who has lived a good life should be rewarded with many men!
It is a very sad sight, to see how the nation that begat Plato and Aristotle ended up debating steppe nomads about whether fornication and divorce makes them worse people. Still, as decayed as Greek intellectuality was, they still could outwit any Muslim with ease. Because Muslims, if well focused for war, at the end of the day are just not a very smart people, even with Asian blood. Christians could not fight, could not administer a state strong enough to fend off their enemies, they couldn't avoid the murder, rape and enslavement of their kin. But hey, they could argue about the Trinity. There must be something addictive about arguing ceaselessly about unfalsifiable crap. But in the end, what mattered was who was holding the stones.