In a culture of moral relativism, presuppositionalism doesn't prove the Word is true — it shows that you can't make sense of truth without the Word

Sye explains: when a relativist says 'your Bible can't be true,' he reveals he believes in truth. Sye's response: 'Where do you get the concept of truth without God?' The presuppositional move is to borrow the concept of truth back to God from the one attacking Scripture. Similarly, the evolutionist who says 'the Bible is not true' is borrowing the concept of truth from God to attack God — Sye illustrates this with the Doug Wilson 'fizzing' argument (evolution means brain is just fizzing chemicals; why would atheistic fizzing be more reliable than theistic fizzing?).