I've been listening most recently to some of Sye ten Bruggencate's apologetic debates and conversations. My goal is always to become a more effective apologist, myself. I'll confess that I spend a lot of time admiring him and his partners and thinking how poorly I'd have done in that situation. But I keep at it, because it's both a Christian's calling and part of the task of being a pastor, whether it comes easily to one or not.
Presuppositionalist apologists like Sye and others argue insistently (and to their opponents' dismay) that anti-Christians' every argument denying God's existence, in fact, proves God's existence. The point is a very good one, but I'm not sure everyone gets it.
Me, I'm simple; so I always chew things over to the point of my own understanding... and by that time, I've got something just about anyone can understand. Usually a good analogy helps me. Here, I think I have one, so I offer it to you, with the disclaimer that every analogy breaks down at some point.
For starters, presups point out that God is not a conclusion, He's the starting-place. Unbelievers hear this as saying we've no proof of God, though it isn't what we're saying nor meaning. I've wondered whether it might not be more effective to say that the truth of God is too big and fundamental to be the conclusion of a syllogism or chain of reasoning. Only truths of a certain size can fit at the end of a chain of reasoning, and the truth of God is too big to come at the end. That truth is so big and fundamental that it only fits at the start; any other location whittles that truth down to unrecognizability.
So here's the analogy. Envision two philosophical combatants. One school, the Floorists, asserts the existence of the floor as that on which everything else necessarily rests. The other (Afloorists) denies that assertion.
The Floorists say, "If there were no floor, we wouldn't even be here. We'd be nowhere. There'd be no connecting-point and no common-ground — literally. And you Afloorists confirm that fact with every word."
The Afloorists scoff. "Prove there's a floor, without standing on one!"
Floorists: "Can't do that."
Afloorists: "Aha! You see? You have no proof!"
Floorists: "No, we can't do that because we can't even have this discussion without resting on a floor. We can't even talk to you without all of us resting on the floor. The only reason we're talking right now is that both of us are resting on a common floor."
Afloorists: "Nonsense! For instance, look here, I'll show you..." (stepping off the couch onto the floor).
Floorist: "Stop. You just proved the floor. Even before you moved, you proved the floor You were sitting on something resting on the floor."
Afloorist: "What? I never did! I'm just showing you, here and..." (taking a second step).
Floorist: "Stop! If there's no floor, you couldn't take a first step, let alone a second. All the time your mouth is running, denying the floor, you're standing on the very floor you deny. Every step you take, denying the floor, depends on the floor. You know that, or you'd not have stepped off so confident that something would support you. Every step you take affirms the floor. If there were no floor, you couldn't walk around denying the floor. Every step proves what your mouth denies."
Afloorist: "Bosh. You just can't prove the floor without assuming the floor. You have no evidence. Here, let me show you another place where there's no floor."
Floorist: "Only if you can do it without resting or walking on the floor."
Afloorist: "We can do that! We all know we can do that! Science has proved we can do that! Your problem is that you can't prove there is a floor!"
Floorist: "You can't even say that without resting on the floor. You're denying the floor that you know exists, and meanwhile you're depending on the floor, to deny the floor."
Afloorist (triumphantly): "Aha! You see? You have no proof! You refuse to prove the floor! We ask for evidence, you give none! You don't prove it here (takes step), or here (takes step), or here (jumps up and down). There is no floor! There. Now I'm going to go have sex, thanks to this exhilarating freedom that Afloorism has brought me."
Floorist: "...on something resting on the floor. Brilliant." (Facepalm.)