In taking Scripture as an absolute presupposition and standard for thought, the Christian apologist ought to maintain that there are no possibilities outside of what God is and decrees to be. It is never possible for God to be other than the type of being He is portrayed to be in His self-revelation. Because he does not presuppose the certain truth of the Bible at the very start of his apologetic (de facto and in principium) Clark (a self-professed Calvinist) is willing to reduce the whole system of Christian truth revealed by God therein to a possible accident!
“Strange accidents do indeed occur, and no proof is forthcoming that the Bible is not such an accident. Unlikely, perhaps, but still possible” (“How may I know the Bible is Inspired?”, Can I Trust My Bible?, 24 Gordon Clark)
Because Clark has this illegitimate notion of possibility in his apologetical system, a notion which lies behind even his beliefs about God and God’s Word, it is inevitable that he should cease to be a genuine presuppositionalist. By not viewing the the truth of Scripture as a presupposition that that is absolutely necessary, Clark reduces the status of the Bible to a hypothesis. The truth of Scripture is not taken to be the case at the outset, so that only later are a man’s thoughts to submit to it. The Christian alternative is one of many possibilities to be explored and evaluated.
~Greg Bahnsen (Presuppositional Apologetics: Stated and Defended; ch 4, pg 146)
This is from Bahnsen’s critique of Gordon’s Clark’s putatively presuppositional apologetic. Note that he takes Clark’s ultimacy of possibility over God to be a capitulation. This is instructive.