“”(T)he only proof for the existence of God is that without God you couldn't prove anything.
|—Cornelius Van Til|
Presuppositionalism is a bullshitting tactic cooked up by Christian apologists when they realized that their old arguments were not working.
Basically, according to presuppositionalists, those pesky atheists, evolutionists, etc., have to presuppose that God does not exist in order to formulate their arguments. (This ignores that many such arguments employ reductio ad absurdum, which does not require such presuppositions; also that most atheists are not so-called "strong" atheists and hence think it's unlikely that God exists, rather than insisting that they "know" he doesn't.)
Furthermore, having established (to their satisfaction) that atheists must have presuppositions, they conclude that they are also allowed to have them. This means that they do not try to argue directly in favor of God's existence, as evidentialists and classicists might, instead presupposing God's existence in all arguments; indeed, they do not accept the validity of any argument that does not draw upon this presupposition.
 Form of the argument
The argument goes something like this:
- Old-School Apologist: Ears up, sinners! Here's an argument that God exists.
- Recalcitrant Sinner: That argument's a pile of bunk! Here's why.
- Old-School Apologist: Oh. Drat.
- Presuppositional Apologist: Fear not, lions of Christ; here comes the new broom! Ears up, sinners! You say all the old-school arguments for God's existence are bunk?
- Recalcitrant Sinner: Yep!
- Presuppositional Apologist: Well, your refutations don't hold water, because they're grounded in the false presupposition that God doesn't exist.
- Recalcitrant Sinner: Uh, no, they're not.
- Presuppositional Apologist: They're grounded in a false presupposition, I say! Now if you'd just presuppose that God exists, it's obvious that God exists!
- Recalcitrant Sinner: And you say we use circular logic...
 Extension: transcendental argument for the existence of God
- Presuppositional Apologist: Did you mention logic? Here is something new for you: Laws of Logic, morality and science are no longer valid unless you assume God exists, because God created logic, the laws of science, and morality.
- Recalcitrant Sinner: That argument's also a pile of bunk! Here's why.
- Presuppositional Apologist: See, you just gave me more proof that God exists because you are using God-created logic, God-created science and God-created morality!
- Recalcitrant Sinner: But if that's true, the laws of logic are valid and that means your argument's a pile of bunk, like I said!
- Presuppositional Apologist: Blasphemer! If God said 2+2=5, then we've got five eyes between us!
- Recalcitrant Sinner: Hello, fellows in white coats? We need you over here pronto.
 Use by creationists
More recently, Creation Ministries International has been holding to the idea of presuppositionalism. In the context of their particular arguments, this means that they have quit insisting that there is any particular evidence in favor of creationism (a necessary position, given that there is none) and started insisting that it is the interpretation of the evidence that the "evolutionists" have wrong, since they presuppose a naturalistic world-view; supposedly, if one interprets the evidence the right way (which involves not only assuming God's existence, but violating Occam's razor every which way to explain away all the contradictions), one will see that it leads undeniably to the Truth™ of God's existence.
Jonathan Sarfati of CMI, in response to a piece on the complexity of the human genome is a proponent of presuppositionalism:
“”Evolution is not based on evidence that speaks for itself; rather, it is a deduction from their own presuppositions—a priori commitments to materialism and rejection of a designer, because they can’t bear a ‘divine foot in the door’. Therefore they have no right to object when Christians start from their own presuppositions ... When the person you talk to on creation insists that you ‘leave the Bible out of it’, they are really saying the deck should be stacked one way.
But then, after insisting that "evolutionists" are not allowed to have the deck stacked their way in an argument, later in the same article he then says that the creationists should be allowed this privilege:
“”We are not merely asking opponents to consider biblical presuppositions as an alternative way of looking at the evidence. Nor are we merely saying that they are ‘nicer’, nor even that they provide a superior framework that better explains the data (although both of these are true as well). Rather, the claim is even stronger: that the biblical framework is the only one that provides the foundation for science, voluntary will, logic and morality.
In short "Their presupposition is wrong because you're not allowed to use presuppositions we dislike. Our presupposition is right because you are required to use presuppositions we approve of".
 See also
- Not Circular Reasoning: An essay by Jonathan Sarfati employing circular reasoning.
- ↑ Rather, they are "weak" atheists who argue that it's best to treat gods as not existing until/unless somebody can prove it or they do.
- ↑ http://creation.com/presuppositionalism-vs-evidentialism-and-is-the-human-genome-simple