I’ve never heard this term. What does it mean?
It’s engagement beginning with presupposing the truth of one’s convictions – kind of “presuming the consequent” as a large scale apologetic.
For example, a Calvinist presup will simply assume upfront, as axiomatic, the literal inerrancy and ultimate authority of the Bible, or more precisely her interpretation of the Bible. That’s it, it’s presumed it’s non-negotatiable, and all communication from that side proceeds only from a firm commitment to that presumption.
That means that, for example, an atheist, despite their claims to the contrary, really does no God exists, for the Bible says in Romans 1 that God’s qualities are clearly seen, and that all men are without excuse in affirming this, and further that suppress the truth by the wickedness… an unbeliever is, on their view, deductively, a liar when he says he sees no evidence for God.
Further, it is presumed that since God created the earth, and man, that God provisioned reason, and logic and morality and knowledge as features of his special creation, meaning, since the presup has taken it as axiomatic that the Bible is authoritative, perspicacious and infallible, that no further explanation for those realities is needed. They are given by God and that’s that.
Now, the atheist is buried under the workload of a stream of demands to justifiy where biological life comes from, reasoning, consciousness, morality, all that, and all with an acute hyper-skepticism that demands exhaustive evidence for all parts and all their constituent parts, but is free to reject or dismiss any or all of that because, again, the presuppositional stance enables them to classify anything that conflicts with their understanding of scripture as false, axiomatically.
Lastly, it is puposely lopsided that way, due to the profound conviction that there is no neutral ground for a believer and an unbeliever to start on and work from, and that it is sinful for the believer to suppose there is, or to proceed as if that was the case. The truth of the Bible as axiomatic simply prevails, and it is just a one way street, a kind of preaching, with the only question being whether the atheist, fool enough to engage in a reasonable way, where points and challenges and evidence can push things one way or another, capitulates to the presuppositionalist’s axioms. The presup declares she has nothing to defend or establish, and that the truth of her positions are all stipulated up front, and the unbeliever is tasked with trying to prove the unprovable, to jump impossible hurdles, for the amusement of the presup, and his own punishment for being wicked enough to be a liar suppressing God’s truth in the first place.
See the enchanting works of Cornelius van Til, Greg Bahnsen, Gary Frame,and Gordon Clark (Clark’s approach is a bit different than classic van Tilian presuppositionalism).
These folks are really wonderful to engage, and a delight at cocktail parties!
-TS