Historically, many Christians have believed that philosophy and theology are enemies. Tertullian's (160-220 CE) famous question, "What has Athens to do with Jerusalem?," is emblematic of this viewpoint. Tertullian, of course, was actually going back to Paul's statement in Colossians 2:8 in which he warned the Christians to be leery of philosophy. Tertullian's full statement reads:
From all these, when the apostle would restrain us, he expressly names philosophy as that which he would have us be on our guard against. Writing to the Colossians, he says, “See that no one beguile you through philosophy and vain deceit, after the tradition of men, and contrary to the wisdom of the Holy Ghost.” He had been at Athens, and had in his interviews (with its philosophers) become acquainted with that human wisdom which pretends to know the truth, whilst it only corrupts it, and is itself divided into its own manifold heresies, by the variety of its mutually repugnant sects. What indeed has Athens to do with Jerusalem? What concord is there between the Academy and the Church? what between heretics and Christians? Our instruction comes from “the porch of Solomon,” who had himself taught that “the Lord should be sought in simplicity of heart.” Away with all attempts to produce a mottled Christianity of Stoic, Platonic, and dialectic composition! (1)
However, in the 1970's a renaissance of interest in utilizing philosophy to better understand theology developed. Whereas philosophy had largely limited itself to basic questions such as the ones discussed in Philosophy of Religion classes, this new breed of Christian philosopher was interested in "making sense" of classic Christian doctrines, such as "Original Sin," the Incarnation and the Atonement. Oliver Crisp explains:
In the 1970's and early 1980's Christian philosophers in the analytic tradition began to turn their attention to making sense of particular Christian doctrines, instead of restricting themselves to the more general topics that fall under the generic 'rubric' 'classical theism,' such as the concept of God, arguments for the existence of God and the problem of evil.(2)
Of course, this attempt to explain theology using the structures and methods of philosophical analysis was not new. It characterized many of the medieval theologians such as Anselm, Thomas Aquinas, and Duns Scotus, as well as later Protestant theologians such as Jonathan Edwards. However, after Kant, many theologians had given up on utilizing philosophy. Philosophers, post-Kant, had been skeptical of talking about theology since they were not sure that we could really know anything beyond our experience. Crisp writes:
[T]hose thinkers whose point of departure is Kant's Copernican Revolution in philosophy, eschew large metaphysical schemes of thought because (following Kant) they are deeply skeptical that any such schemes are possible. All we can conceive of in our theology and philosophy is that which is phenomenal, a part of this world of sensation in which we live, not the realm of the noumenal, the eternal and unchanging, that is forever beyond us.(3)
Another problem for theologians who wanted to utilize philosophy was "logical positivism" (4) which dominated the first half of the 20th century. Logical positivists maintained that all "God-talk" was meaningless since it could not be verified empirically. When it fell out of favor in the 1960's, the soil became fertile again for the rise of philosophical theology and philosophical apologetics. In 1967, Alvin Plantinga wrote his first volume, God and Other Minds: A Study of the Rational Justification of Belief in God, which laid the epistemological foundation for the resurgence of serious philosophical discussion of theological matters. In 1974, the Evangelical Philosophical Society (5) was founded and in 1978, the Society of Christian Philosophers (6).
This re-birth of "Christian philosophy" also corresponds to the renaissance of evangelical Christian apologetics. In 1976, Norman Geisler, a Christian philosopher in the Thomist tradition (Ph.D. Loyola University) published his first apologetic work entitled, Christian Apologetics, and Gordon Lewis published, Testing Christianity's Truth Claims. In 1981, William Lane Craig published his first apologetic work entitled, The Son Rises and in 1984, Reasonable Faith. It was now acceptable for conservative Christians to make use of philosophical arguments in defense of the faith.
However, not all conservative Christians were receptive to this new marriage between philosophy and theology. Some Reformed theologians, especially those of the presuppositional school, were leery. That is because they saw philosophy as man's reason usurping authority over sacred writ. In other words, philosophical theologians make it their goal to "make sense" out of Christian doctrines. They want to explain how such doctrines as original sin, the atonement, the resurrection, and so on, can be understood and explained philosophically. Philosophical theologians begin with the assumption that man is created in the image of God and is endowed with certain rational and moral sensibilities which make him able to "think God's thoughts after him." Reformed theologians, on the other hand , have typically held that not only is man's heart fallen but his head is fallen as well. In contrast to Aquinas, they have held that the image of God in man is so twisted and deformed that the unregenerate man can no longer "think God's thoughts after him." Man's intellect is fallen as much as his will is fallen. Therefore, they believe that is why Paul said in 1 Corinthians chapter 1 that the preaching of the cross was foolishness to the Greeks (i.e, the philosophical crowd). The Reformed would say that not only is it a waste of time to try to justify God's ways to unregenerate man but, that more seriously, it exalts human reason to the place of ultimate authority. Philosophical theologians, in their opinion, are guilty of judging and evaluating doctrine based not on whether its exegetically based in the Scripture but on the grounds of whether it makes sense logically and whether it is in tune with man's moral intuitions. Thus, they view philosophical theology with great suspicion as having reformulated doctrine into a form that will be palatable to the unregenerate mind. In J. I. Packer's words, they have surrendered the home field advantage of Scripture to play on their enemies' field, reason (7).
According to Greg Bahnsen:
The Christian does not look at the evidence impartially, standing on neutral ground with the unbeliever, waiting to see if the evidence warrants trust in God's truthfulness or not. Rather, he begins by submitting to the truth of God, preferring to view every man as a liar if he contradicts God's word (cf. Rom. 3:4). . . . By trying to build up a proof of the resurrection from unbiased grounds the Christian allows his witness to be absorbed into a pagan framework and reduces the antithesis between himself and the skeptic to a matter of a few particulars.(8)
I have to agree with the Reformed presuppositionalists. It is not possible to explain rationally the doctrines of the Trinity, the incarnation, and the Atonement. These doctrines, as well as other Christian doctrines, are filled with internal contradictions and inconsistencies. One would reject them as irrational, unless one had first presupposed that the Bible is a divine revelation and must be believed even if it doesn't "make sense." The problem, with presupposing the truth of the Bible is, of course, that it is merely "begging the question." One has decided in advance that the Bible is true and will interpret all evidence to agree with that presupposition. For that reason, William Craig, a philosophical theologian and apologist, rejects presuppositionalism. He writes:
Where presuppositionalism muddies the waters is in its apologetic methodology. As commonly understood, presuppositionalism is guilty of a logical howler: it commits the informal fallacy of "petitio principii," or begging the question, for its advocates presupposing the truth of Christian theism in order to prove Christian theism. (9)
In reality, though, Craig does the same thing as the presuppositionalists. While he pretends to be concerned about evidence and reason, he acknowledges that at the end of the day, he "knows" Christianity is true because of a subjective religious experience which he calls the "witness of the Spirit" (see here).
So, Philosophical Theology fails in my opinion because it is impossible to “make sense” of Christian doctrines such as the atonement, the incarnation, the Trinity, and so on. One believes these doctrines because of an appeal to religious experience or religious authority not because of evidence or reason and when one tries to employ reason to understand the doctrines, the attempt fails. Thus, I decided to reject Evangelical Christianity. Its doctrines can only be believed by sacrificing reason. If there really is a god(s), it doesn't seem that he/she/it would require one to go against reason. I could accept the idea that revelation from a divine source might transcend reason but I cannot accept the idea that it would contradict reason (10).
(1)On the Prescription of Heretics, ch. 7.
(2) A Reader in Contemporary Philosophical Theology (2009), p. 1. Alvin Plantinga defines Philosophical Theology as a matter of thinking about central doctrines of the Christian faith from a philosophical perspective; it is a matter of employing the resources of philosophy to deepen our grasp and understanding of them ("Christian Philosophy at the End of the Twentieth Century," in James F. Sennett (ed), The Analytic Theist, An Alvin Plantinga Reader (1998), p. 340.
(3)Crisp, p. 4; also see Nicholas Wolterstorff, "Is it Possible and Desirable for Theologians to Recover from Kant," in Modern Theology 14 : 1-18.
(4)Logical positivism is a philosophical doctrine formulated in Vienna in the 1920s, according to which scientific knowledge is the only kind of factual knowledge and all traditional metaphysical doctrines are to be rejected as meaningless. "Logical Positivism," Encyclopedia Brittanica (2010).
(5) According to the Vision Statement on their website, The Evangelical Philosophical Society (EPS) is a professional society of Christian philosophers who are committed to a high view of biblical authority and who believe that the gospel of Jesus Christ is true, intellectually persuasive, and rationally defensible in the marketplace of ideas. Past presidents of the society have included: Norman Geisler, Gordon Lewis, Paul Feinberg, John Jefferson Davis, and Gary Habermas. The Journal for the Society is called: Philosophia Christi.
(6) According to their website, the purpose of the Society of Christian Philosophers is to promote fellowship among Christian Philosophers and to stimulate study and discussion of issues which arise from their Christian and philosophical commitments. William Alston, Robert Merrihew Adams, Alvin Plantinga, Marilyn McCord Adams, George Mavrodes, Nicholas Wolterstorff, Eleonore Stump, and C. Stephen Evans are among the past Presidents of the Society. Their journal is entitled: Faith and Philosophy.
(7)The Logic of Penal Substitution (1974).
(8) Greg Bahnsen, The Impropriety of Evidentially Arguing for the Resurrection (1972).
(9) Five Views on Apologetics, ed. Steven Cowan (2000), p. 217.
(10) What I mean by “transcend reason” is that it is not fully comprehensible. However, if what is comprehensible in the revelation contradicts reason, then I don’t see how it can be true.