Indeed, my absence this weekend has allowed the HP to elaborate the main thrust of the argument clearly and succinctly.
I would like to elaborate on the points he has raised, taking as my starting point his invocation of St. Thomas Aquinas.
I am fairly certain the HP, in invoking the Angelic Doctor, had in mind the following text from the opening paragraphs of the Summa contra gentes:
To proceed against individual errors, however, is a difficult business, and this for two reasons. In the first place, it is difficult because the sacrilegious remarks of individual men who have erred are not so well known to us so that we may use what they say as the basis of proceeding to a refutation of their errors. This is, indeed, the method that the ancient Doctors of the Church used in the refutation of the errors of the Gentiles. For they could know the positions taken by the Gentiles since they themselves had been Gentiles, or at least had lived among the Gentiles and had been instructed in their teaching. In the second place, it is difficult because some of them, such as the Mohammedans and the pagans, do not agree with us in accepting the authority of any Scripture, by which they may be convinced of their error. Thus, against the Jews we are able to argue by means of the Old Testament, while against heretics we are able to argue by means of the New Testament. But the Muslims and the pagans accept neither the one nor the other. We must, therefore, have recourse to the natural reason, to which all men are forced to give their assent. However, it is true, in divine matters the natural reason has its failings. SCG I.2.iii (quoting from the Pegis translation of Book I, available in its entirety here)The reason for which the Old and New Testaments are useless for the purposes of proving the erroneous nature of pagan theology, should be clear: the OT and NT are not their sacred texts - which is to say they are not recognized as authoritative. An appeal to their contents canot, therefore, serve as proof of a disputed question.
The Old and New Testaments are similarly useless for the purposes of theological disputation with Muslims. The reason for this is the supersessionist presupposition of Islam: the Qur'an is God's final reveleation, and it replaces His earlier revelations. Importantly, the principle is applied to interpretation of the Qur'an itself, as well - later verses (surrahs) control earlier ones, so the question of a surrah's composition (the question as to when a verse was "handed down" to use the Muslims' own technical terminology) becomes essential (and we will see why this matters later on, when we consider a specific case).
If, therefore, we are to convince a Muslim interlocutor of the truth of Christianity, we have no choice but to begin by proving that the Qur'an is not plausible as the definitive statement of God's revelation to humanity, and so on the grounds that it directly and irreconcilably contradicts at least one of the ultimate truths, which human beings may know by the working of reason without an appeal to the authority of the data of faith.
On this reading, the science of philosophy provides the only space for dialogue among Christians and Muslims.
That Christians can practice philosophy without compromising their faith commitments is a long-established fact in the Catholic tradition.
Muslims, however, are necessarily embarrassed by philosophical dialogue, and so for two reasons, one "doctrinal" and the other historical, though closely and perceptably linked to the doctrinal reason.
Basically, one becomes a Muslim by making an act of islam - of submission - to the will of the One God. The will of the One God is manifest in al-Qur'an, literally the prounouncement, or promulgation (or declamation or recitation) of God's prophet, a merchant named Muhammad.
According to this al-Qur'an, this pronouncement, God is perfectly One, absolutely transcendent, and utterly ineffable. Even His one-ness is known only and entirely through submission to His manifest will. To make any attempt to penetrate, by means of human reason, the inner life of the Divine, were to risk impiety.
The end of philosophy is precisely the knoweldge of God.
So, the Muslim finds himself under a sort of crisis whenever he attempts to think God's thoughts, as it were.
This, on its own, were not enough to exclude the Muslims from philosophy a priori. Indeed, there were, during the first few centuries of Islamic ascendancy, thriving schools of speculative theology, and the thought of the principal exponents of those schools greatly influenced Western intellectual history.
The problem is, the schools were suppressed, and most of the teachers executed, banished, forced to recant or otherwise silenced - and this was not an accident.
The Arabic word for speculative conversation is kalaam, which ideally renders the Greek dia-logos, from which we have the English, "dialogue". The question in the first few Islamic centuries was which would be the chief science: would it be kalaam, or rather the positive legal science known as Shari'a, roughly, "the way" or "the path"? The Muslim world, through its leaders, opted for that, which is admittedly the more internally coherent alternative: the primacy of positive legal science.
Now the problem comes fully into view: speculative reason cannot submit to positive law, and remain properly speculative. To insist on the primacy of positive legal science entails not merely the demotion of speculative reason, but the dismissal of speculation as basically irrelevant to the human community.
Said shortly, the current state of Islamic self-understanding is such that dialogue among speculative thinkers is not so much impossible, as it is irrelevant.
What must be found is a way to enter conversation with Muslim legal scholars, who alone speak authoritatively within their communities.
More on this next time...