A friend of mine, who is quite appreciative of the presuppositional approach to apologetics, nevertheless argues that it is only useful when dealing with unbelief. However, once a person is convinced of a “general theism,” for example Islam, then the transcendental argument (TAG) is no longer relevant. Because of this, I have long been intending to do some work on presuppositionalism and Islam. Until then, I am happy to recommend the following blogpost found at “Choosing Hats” on the subject.
In this Chris Bolt says, “If TAG only proves general theism then a great many of the objections raised against traditional proofs for God apply to TAG as well…Believing that TAG only establishes the existence or rational necessity of the classical theistic god or ‘general theism’ (if it even establishes that) carries with it a long list of implications that I believe result in serious enough inconsistencies as to be worth rejecting along with their source.”
He explains the transcendental approach–what he calls “covenantal apologetics”–with an eye towards Islam. I found this to be helpful and would love to see more work done on this area. Bolt says, “While we are not to answer the Muslim according to his or her ultimate anti-Christ presuppositions we are nevertheless to answer the Muslim. This time the Muslim must be answered in accordance with his or her false presuppositions. The Muslim believes things that are not true because they do not comport with what God tells us. Hence the Muslim view is absurd and we can demonstrate such by pointing out its inconsistencies when it is taken as a whole on its own terms and thought through carefully. Islam will not be implicitly accepted by the Christian in apologetic discussion, but Islam will be treated “fairly” according to its own presuppositions and the way that they work out in accordance with the Islamic variety of the denial of the Christian worldview.”
Of course, the key difference between Christianity and Islam is that the Christian God is Triune, that is, God is one in essence and three in person (Father, Son, Holy Spirit). Islam, on the otherhand, posits a god who is radically one with no distinction or plurality. He is a divine monad. This is distinction is important: “The ontological co-ultimacy of unity and plurality in God (as may be observed since finitely displayed on a derivative creaturely level) makes human epistemology possible as a result of God’s nature and knowing. The reason that we are able to make sense of the world is because the Triune God of Scripture exists. The Christian worldview is sufficient to account for human intelligibility at least with respect to unity and plurality.” The god of Islam, because of his monadic character, is not able to account for human intelligibility.
Why is this the case? According to Bolt, “If it is the case that ultimately everything is ontologically unity then the plurality assumed in the affirmation of the proposition ‘Allah exists’ as exhibited in the two words, their many letters, the distinction between existence and non-existence, Allah as distinct from other gods and God, etc. is principally unintelligible. The reason for this is that if reality is ultimately “one” then distinctions of any sort are impossible – which is absurd.”