are false and/or incoherent in many of their formulations, but hide nuggets of truth that can excavated and refined and reformulated in ways that are rationally acceptable. An example of this is Kant's project in Religion Within the Limits of Reason Alone.
Dr Vallicella posits five possible attitudes towards Christian dogmas. What he does not do is distinguish the attitude of the Christian philosopher against any possible attitude of the non-Christian philosopher. The attitude of the Christian philosopher is, in its classic formulation from St Anselm, who got it from St Augustine, credo ut intellegam, I believe so that I may understand.
Now I agree, with Fr John Wippel against Etienne Gilson and the earlier Maritain, that there is no such thing as a "Christian philosophy". There is just philosophy, practiced by Christians and by non-Christians. Sometimes the practice of philosophy can be a praeambulum to Christianity, as in the case of St Justin Martyr and many other famous and less-famous cases. But philosophizing per se is not a religious activity and has no essentially religious content. Philosophy is the unrestricted and holistic application of reason to life.
That being said, philosophizing doesn't happen in a vacuum. Man is a rational, but also a religious animal. Socrates questioned the stories of the poets about the gods, but, contrary to his accusers, did not challenge or reject the gods of the city, much less the existence of the God of philosophy, the One - whoever he was - that gave him his vocation. And Aristotle always took as his starting-point on any particular issue the doxa, the opinions of the common man and of his own philosophical predecessors, rejecting what was faulty or inadequate in favor of a better formulation, but never assuming that the doxa were to be utterly rejected and replaced by complete novelties. This would be hubristically and arrogantly to assume that oneself is already wise and that all other men have always been fools.
The Christian philosopher, then, doesn't have some special kind of philosophy that atheists or pagans don't have; but at the same time he doesn't begin philosophizing neutrally, as though everything he believes might just as well turn out to be false. If modern philosophy has given us one apodictic certitude it's that radical Cartesian doubt is foolish, that it begins with nothing and ends with nothing, or worse. This is not to say that the philosopher holds rigidly to his beliefs no matter what the result of his reasoning, either: otherwise the notion of rational conversion would be absurd. But philosophes have not only gone from Christianity to apostasy and libertinism under the influence of reason; they have also gone from any number of positions to a rational Christianity. I myself am a convert to the Catholic Church.
One does not reason to Christianity or reason to Catholicism in the sense that philosophy ever proves (in any sense) that the Christian doctrines are true. On the other hand, neither does one prove against Descartes or Kant that we experience the world, or that we are awake. We can't prove everything, because doing so would produce an infinite regress. We can however show that to believe that I am now, as I write, am asleep is absurd, that to deny that I experience the world is unreasonable. We can also argue that the doctrines of Christianity are not unreasonable. This does not show that they are true, but it shows that I might reasonably believe that they are true. And if I believe that they are true, I can think about them rationally and philosophically as truths.
The orientation towards religious doctrines as truths - not as puzzles, not as myths, not as more or less acceptable attempts at formulating truths - is the attitude of the credo ut intellegam. It is fundamentally different from the attitude an unbeliever like Dr Vallicella will take towards them. The Anselmian formulation is paralleled by the Augustinian one, "unless you believe you will not understand" - not because the doctrines of the faith are unreasonable or unintelligible, but because without the light of faith the thinker will remain like Aristotle's blind man reasoning about colors: the syllogisms may be logically valid but the thinker will have no way to know to what extent they relate to reality. It's as though a Cartesian were to entertain, but merely as an amusing hypothesis, his existence outside of his brain-vat; except that (in my opinion) real existential Cartesian doubt is absurd and impossible, but real religious doubt is not. The existence of a subjective world of beings beyond my experience of an objective world constituted and co-caused by my mental activity is self-evident, its contrary formulated only with enormous difficulty and under the influence of powerful sophistries; I don't perceive the truth of religious doctrine in the same way or with the same rational force.
There is an ineradicable element of will in belief, analogous to accepting that someone loves me. I can know that my wife exists and that she has a mind like mine; but that she loves me, and that her love is the key fact whereby I ought to interpret her words and actions towards me rather than some more cynical alternative, is not unreasonable, but is also unprovable: I must choose to accept or not accept it, and act accordingly. The unbelieving philosopher, like the suspicious spouse, has access to all the same data as the believer, but sees that the data can rationally be taken another way, and wills so to take it or to abstain from committing to a judgment one way or the other.
The Christian philosopher then is not simply a thinker who chooses to think about the dogmas of Christianity, rather than some other puzzles, or one who finds the traditional dogmatic solutions to the puzzles the most rationally satisfying (this is the entirely modern phenomenon of "philosophy of religion" which, insofar as it is separate on the one hand from metaphysics and on the other from theology, I abominate and abhor). Like the philosopher of the ancient schools, or the modern existentialist, his discipline is not (merely) a logical game or a quasi-scientific method or technique, but an approach (among possible approaches) to being. He is a philosopher who believes in God, Christ, the sacraments, Mary and the Saints, sin, heaven and hell, as he believes in friendship and in love, as unprovable but obviously there; who approaches his God rationally as he approaches his own soul and the world, as concrete beings in need of rational explication; who looks to philosophy to help him both think and live, but who looks to religion, as to direct experience, to provide the things to think about and live among and towards.