I've written several posts on this blog about why I think omniscience is a precondition for knowledge (read and follow the links provided in this link). I haven't explained the full import I think this argument has, however, and a part of the reason is that I'm still turning it over in my mind. I think the last few paragraphs of Steve Matthew's latest review of Clark's A Christian View of Men and Things (link) provides a fine occasion for this discussion and some other points I've been meaning to address:
Clark tells us that if we can logically demonstrate that a system of thought has at least one contradiction in it, that system must be false. This is an application of what is called the coherence theory of truth, which holds that truth must be non-contradictory. Writing in his essay Presuppositional Apologetics: Stated and Defended, Gary Crampton says the following about the coherence theory of truth,“Logic in the Clarkian view functions a a negative test for truth. It is an apologetic tool to show how a contradiction in any system (which all non-believing systems contain) disproves it as a valid system. Logical coherence is a very valid way to proof-text a system for its validity or non-validity. The fact that the Bible is logically consistent does not prove it to be true, but it certainly shows the non-believer that the Christian worldview is based on a system of truth that is logically coherent.”In other words, we do not prove the Bible is true by testing it for logical coherence – we know it is logically coherent because God tells us in Scripture that this is the case, God is not the author of confusion (1Cor.14:33) – but we can disprove other systems of thought by exposing their internal contradictions. The Bible tells us the wisdom of this world is foolishness (1Cor.3:19). It is the job of the Christian apologist to make this foolishness evident.
Clark asserted inconsistency invalidates worldviews; on the other hand, Clark did not assert consistency alone validates a worldview. For example, compare what Gordon Lewis stated about Clark's position in Testing Christianity's Truth Claims (pg. 119-122) with Clark's response in Clark and His Critics (pgs. 399-403). I may reproduce the exchange in a different post, but one critical point is that Clark denied Lewis' claim that he, Clark, had ever asserted or implied that consistency is the sole test of truth-claims. Having read much of what Clark has written, I came to the same conclusion (e.g. points 3-7 here) before even knowing about this rebuttal of Clark.
To understand what Clark is doing, consider the following observation of a prominent, contemporary epistemologist (link):
The classic test for whether a condition for knowledge, say the truth of what is believed, is analytically necessary is whether or not it is absolutely inconceivable that someone has knowledge while failing to satisfy the condition. The test for whether a conjunction of conditions X is jointly sufficient for knowledge is whether we can conceive of X obtaining without knowledge.
Clark's use of logic as an elenctic apologetic implies Clark regards logic as a precondition for knowledge. Since he's right, by applying the test of logic to worldviews, those which are illogical can be discarded, as the do not satisfy a precondition for knowledge. However, this is not to suggest that consistency alone suffices as a precondition for knowledge. Clark noted in his response to Lewis that there are several competing theories of mathematics which are each consistent, or at least seemingly so. But what do geometrical systems have to do with epistemological systems? When Gilbert Weaver mistook Clark for thinking Bertrand Russell was consistent when, in fact, Clark's point was that Russell was only relatively consistent, in his reply to Weaver, Clark even admitted that even if he was unable to discover inconsistency in Russell, his limitations would not imply Russell was consistent (Clark and His Critics, pgs. 283, 291). Clark was clearly not a rationalist. However, he was rational insofar as he recognized logic to be a necessary precondition for knowledge. As Clark stated in this same reply to Weaver (pg. 290), he regarded Scripture as the sufficient precondition for knowledge of truth:
...I "supplement" consistency by an appeal to the Scripture for the determination of particular truths...
He states the same ideas elsewhere. For instance:
The initial implausibility of a thorough-going, all comprehensive system of axioms and theorems does not lie in the fact that it is a hitherto unrealized ideal. The implausibility rests on the contrast between the common opinion that the secular sciences are true, at least largely true, and the implication of Christian axiomatization that they are all completely false… the present point is simply that God is the origin of all truth. Then all truth is one and self-consistent. But if so, non-Christian systems of thought must be false... (Karl Barth's Theological Method, pg. 97)
Here, of course, Clark has in mind the Christian God who has revealed Himself by His word and thereby given His people access to the source of knowledge. Or, as I wrote in a recent post: "God can univocally communicate His eternal thoughts to man by divine illumination pertaining to what He has revealed in His word."
But in addition to conveying the true worldview, Clark also recognized the place of refutation in apologetics. It is conducive to an unbeliever's understanding to refute his worldview by employing a necessary precondition of knowledge, like logic, rather than simply quoting Scripture. The more cognitive dissonance one can create in an unbeliever's mind, the better.
This brings me to the point of my post: the more necessary preconditions of knowledge one can construct and utilize, the more quickly and efficiently a Scripturalist can create this cognitive dissonance by showing that an unbeliever's worldview fails to satisfy these preconditions. I think significant progress can be made in Scripturalist apologetics along these lines.
However, cannot all propositions in Scripture be considered necessary preconditions for knowledge if the theory that all propositions are related is true? It would seem so. But this is a good thing, I think. For one thing, it's a reason Jews cannot copy Scripturalism. But then, on what basis should a Christian choose from the sufficient precondition of knowledge (Scripture) various necessary conditions for knowledge (e.g. logic a la Clark)?
That all propositions are related doesn't mean all propositions are epistemically equal, so to speak, for some are entailed by, justified by, or deduced from others (etc.). While the claims of consistency in Scripture may not actually be falsifiable, they are testable by means of, say, logic. This is one of the more fundamental propositions by which we can test for knowledge. Rather than classical apologetics, which attempts to reason from common assumptions to God, then, this could be called epistemic apologetics, which aims to show what are the fundamental propositions without which knowledge is impossible.
Given that Scripture is the sufficient precondition for knowledge, Christians are already ahead of the curve in a search for these necessary preconditions for knowledge, for the sufficient precondition itself will already entail them. In addition to logic and divine omniscience - including what can be further inferred from those preconditions - I think language as a necessary precondition for knowledge is an avenue Scripturalists have yet to fully appreciate, especially in a practical sense. It is the responsibility of the Christian apologist to study Scripture to find them and learn how to appropriate them. Even one precondition is enough, as in Clark's case. At any rate, they can be distinguished but never ultimately abstracted from the harmonious system in which they are found (Scripturalism):
Axiomatization is simply the perfecting and exhibiting of the logical consistency of a system of thought. In view of Calvinism’s well known reputation for consistency, axiomatization and Calvinism should get along well together. The many theorems derived from the smallest possible number of axioms… And since the axioms, if there be several, depend for their meaning on their interrelationships, axiomatization would rule out the possibility of even a single axiom in common. (Karl Barth's Theological Method, pg. 95)