b) “Presuppositional apologetics commits the informal fallacy of begging the question, for it advocates presupposing the truth of Christian theism in order to prove Christian theism” (William Lane Craig)
Not really. A presuppositionalist says: “God is our ultimate authority. God presents Himself as such and we talk about Him as such. Therefore we can’t go outside of our ultimate authority in order to prove it. When God made His promise to Abraham, since there was no one greater for Him to swear by, He swore by Himself (Hebrews 6:13).” Because God is the ultimate authority He doesn’t appeal to anyone but to Himself, and since the Bible is the His word, nothing can be over the Bible in terms of authority. That is to say the whole Christian worldview is our presupposition. The informal fallacy of begging the question simply stated is: you say something is true because it is true. Put in a logical syllogism.
This is not Presuppositionalism at all. Rather we are arguing from a transcendental necessity of God’s existence. To put it in a logical syllogism:
Or to put it yet another way, presuppositionalism argues using a logical form known as “Proof by contradiction” (also sometimes called reductio ad impossibilem). This is a form of indirect proof which assumes the opposite proposition to be true and then shows that such an assumption leads to contradiction or absurdity.
When we are talking with unbelievers, we ask them to assume that the Christian worldview is not true and see what that would lead to. Of course unbelievers will - as we should expect them to - object to our first premise, claiming it hasn’t been defended. This is why we are engaged in apologetic discussion - to find out if unbelievers can justify rational thought without God. We might have to keep doing this over and over again, not because the argument isn’t valid or isn’t strong, but because whoever you are talking with has no other choice than to repent or embrace absurdity; because they are made in God’s image, it's almost impossible for them to accept absurdity, and because they are not seeking God, they will keep trying to find a justification for their position.
The German philosopher Nietzsche understood the implication of his declaration “God is dead.” He said: “Is not the greatness of this deed too great for us? Must we ourselves not become gods simply to appear worthy of it?” He knew that by rejecting God, man must find another foundation: man must become god. Later in his writing, he said: “I am afraid we are not rid of God because we still have faith in grammar” (Freidrich Nietzsche, Twilight of the Idols, p. 5). Nietzsche is one of the few who tried to embrace the absurdity of their worldview but found it impossible; he discovered that if he is to really get rid of God, he couldn’t have faith in anything else - not even in grammar.