“A transcendental argument begins with any item of experience or belief whatsoever and proceeds, by critical analysis, to ask what conditions (or what other beliefs) would need to be true in order for that original experience or belief to make sense, be meaningful, or be intelligible to us. Now then, if we should go back and negate the statement of that original belief (or consider a contrary experience), the transcendental analysis (if originally cogent or sound) would nevertheless reach the very same conclusion.” (Bahnsen, Van Til’s Apologetic, 501-502.)


That quote by Bahnsen has been misunderstood, abused and hijacked by those who would claim Bahnsen and those who would have nothing to do with his apologetic.
Let’s take this quote of Bahnsen’s step by step.

1. “A transcendental argument begins with any item of experience or belief whatsoever”
Let’s assume as our belief that there is causality. That it is intelligible.

2. “…and proceeds, by critical analysis, to ask what conditions (or what other beliefs) would need to be true in order for that original experience or belief to make sense, be meaningful, or be intelligible to us.”

Let’s assume that what must be the necessary precondition needed to make sense of causality is God’s existence. We are now left with: If Causality, then God.

3. “Now then, if we should go back and negate the statement of that original belief (or consider a contrary experience), the transcendental analysis (if originally cogent or sound) would nevertheless reach the very same conclusion.”
Now let’s do as Bahnsen suggests and “negate the statement of that original belief”. In other words, let’s negate causality (the statement of that original belief) and see if we reach the same conclusion.

At this juncture we have two choices. The first one is a bit strange but let’s run with it and see where it takes us. (A) We can first interpret the instruction in such a manner as to introduce a minor premise thereby denying the antecedent of the major premise while affirming the consequent in the conclusion. Does Bahnsen mean this?

If Causality, then God (because causality presupposes God)
~Causality
Therefore, God.
What is the problem with such a rendering of Bahnens’s words? To argue as above is to draw a conclusion that does not follow from the premises in any logical sense! The argument is invalid (and no appeal to transcendental arguments can save a formal fallacy.) Whenever possible, we should not interpret someone’s words in such a way that makes him out to look foolish or inept.

Therefore, let’s consider another way to heed the instruction to “negate the statement of that original belief”. (B) Let's interpret the instruction in such a manner as to deny the statement of that original belief not in the minor premise but in the major premise. Again, we are told to go back and negate the statement of that original belief in order to see if both the first belief and its denial lead to the same transcendental conclusion. When we do that, we are left with two different major premises that both are to lead to the same conclusion. We're left with the original premise (or belief): If Causality, then God; but also we’re left to consider the negation of that original belief with another premise: If ~Causality, then God. That rendering with respect to form is consistent with Don Collett's rendering of CVT and TAG in the WTJ:
C presupposes G if and only if both 1 & 2:
1. If C then God exists
2. If ~C then God exists
Whether we predicate: If Causality, then God (or) If ~Causality, then God the same conclusion, God, obtains. In other words, God is the necessary precondition for all predication. Or to put it in Bahnsen’s terms, whether we affirm or deny the original belief, the transcendental analysis nevertheless reaches the very same conclusion given both premises. {NOTE WELL: We are not negating the metaphysicality of causality but rather the truth value of the predication of the metaphysicality of causality! In other words: ~causality (which is chaos) does not presuppose God(!), but indeed the belief or assertion of ~causality does! In other words, the concept of non-causality presupposes God.}
The second way ought to be considered the most reasonable way in which we ought to interpret the instruction. There are two reasons for this. First, the second way is not an invalid argument as is the first way; and if we are able to interpret someone’s words in a way that is cogent rather than foolish, then we should. Secondly, it has not been shown that the author of the quote ever demonstrated in his many lectures and debates a single instance of fallaciously denying the antecedent while affirming the consequent. Yet on many occasions he labored the point that to argue against the Christian worldview, the Christian worldview must first be presupposed. And that is to argue both:

If sound argumentation, then God (since sound argumentation presupposes God)
and
If unsound argumentation, then God (since unsound argumentation... God)

When we work these arguments through, we find:

If sound arguments, then God...
~God
Therefore, no sound argument... but there are sound arguments, therefore, God
and

If unsound arguments, then God...
~God
Therefore, no unsound arguments... but there are unsound arguments, therefore, God
Accordingly, whether we affirm sound arguments "or go back and negate" sound arguments, the same transcendental conclusion obtains - God!

Therefore:

If sound or unsound arguments, then God
~God
Therefore, no sound or unsound arguments (but there as such arguments, therefore, God)

The deductive argument, which is transcendental in nature, establishes God as the necessary precondition for both sound and unsound arguments. TAG, however, must be distinguised from garden variety deduction, as I show here:

Finally, TAG and Bahnsen has nothing to do with anything so silly as:
If sound argument, then God
Not sound argument
Therefore, God
In the final analyses, Bahnsen’s statement need not lead us into fallacious reasoning. Added to that, it is only when we interpret Bahnen’s statement in such a manner as not to be fallacious are we able to reconcile his summary statement with his many demonstrations of what the statement contemplates. Why not, therefore, let Bahnsen not be fallacious, especially if it allows him to be consistent with himself?