The Preconditions of Knowledge

Expanding my study of Christian Epistemology I’ve started reading a number of thinkers beyond Gordon Clark, on whom I am writing a biography.  Included in my recent readings have been Cornelius Van Til and John Frame who each put emphasis on the Transcendental Argument for the Existence of God (TAG).
The TAG attempts to prove God’s existence by the impossibility of the contrary.  Specifically, they argue, the God of the Bible is a necessary precondition for intelligibility of the world.  Without God, who brings order to the world, one could not have knowledge at all.  Thus, they believe, ALL non-Christian philosophies are self-defeating.
I’m not convinced of the validity of the TAG.   Although certainly SOME non-Christian philosophies are self-contradictory, I do not know that ALL of them are.  Furthermore, proof of the TAG seems to only give us Theism and not Christianity itself.  Van Til made a further argument supporting the existence of a trinitarian God, but even if that were proven we only have trinitarian theism, not Christianity. Rather, I’m convinced to have Christianity, we must have the Bible itself.  It is the Bible, as our epistemological given, that gives us Christianity. It is the validity of the Bible, not TAG that we should start with.
But, all of this makes me think, “what are the preconditions of knowledge?”  Before I read Van Til, Frame, and others more thoroughly, I want to give a stab at what I think the answer might be.
1. Something other than the knower must exist to be known about
2. The knower must himself exist
3. A process must exist by which to distinguish truth from falsity.
4. As a corollary to 3, truth must exist.
Any philosophy that rejects one of these tenants would be self-defeating.  It would eliminate it’s own preconditions of knowledge. Certainly there are philosophies that reject 4), that truth exists.  Those can be easily rejected.  However, most all would accept 1 and 2 and claim an answer for 3.  It is 3, the process by which we distinguish truth from falsity that is really the critical question of epistemology.