The Transcendental Argument for God’s existence is one that has gained much attention over the last 30 years since it’s prominent featuring in a 1985 debate between Dr. Greg Bahnsen and Gordon Stein . In this debate, we can see the so-called “presuppositional force” of Bahnsen’s argument against Stein on the grounds that Christian theism provides the best and proper basis for logical and moral truths. This basis which, Bahnsen concedes to arguing on the grounds of Christian theism rather than general theism . For instance, Bahnsen in his opening remarks states:
I want to specify that I’m arguing particularly in favor of Christian theism, and for it as a unit or system of thought and not for anything like theism in general, and there are reasons for that. The various conceptions of deity found in world religions are in most cases logically incompatible, leaving no unambiguous sense to general theism – whatever that might be. 
Hence, he further clarifies that his argument will be concerned with “the objective merits of the case which can be made for atheism or Christian theism, not related subjective or personal matters.” Though the thesis of Bahnsen may appear considerate and so on, just what exactly is his defense of Christian theism getting at? Bahnsen is using Transcendental Logic in order to demonstrate the “objectively true” basis of Christian theism. Transcendental Arguments, thence, as defined by Robert Stern (1999):
Perhaps the most definitive feature…. [of TAs] is that these arguments involve a claim of a distinctive form: namely, that one thing (X) is a necessary condition for the possibility of something else (Y), so that [ … ] the latter (Y) cannot obtain without the former (X). In suggesting that X is a condition for Y in this way, this claim is supposed to be metaphysical and a priori, and not merely natural and a posteriori: that is, if Y cannot obtain without X, this is not just because certain natural laws governing the actual world and discoverable by the empirical sciences make this impossible (in the way that, for example, life cannot exist without oxygen), but because certain metaphysical constraints that can be established by reflection make X a condition for Y in every possible world (for example, existence is a condition for though, as the former is metaphysically required in order to do or be anything at all). 
Sean Choi also pretexts the definition of Stern by stating Transcendental Arguments as “deductive [ … ] in nature,”  while also exhibiting a particular form (that form being, Stern 1999). The general form of a Transcendental Arguments (TAs) are as follows:
- (TA1) q
- (TA2) It is necessary that: if not-p, then not-q
- (TA3) So, p.
The proposition q in both (TA1) and (TA2) takes its form as a proposition that gathers its value in particular propositions pertaining to some given phenomenon (e.g., logic, morality, truth, etc.) that can be accounted for or asserted without any dispute in question provided the philosophical context in question. That criterion in order thus leads proposition (TA1) – or q – to obtain and be considered a fact.
However, as for the given proposition p as seen in (TA2) and (TA3), p is a variable that takes its value concerning some other given phenomenon that is just as well claimed to be a fact and functions as a necessary precondition for the truth-hood of the phenomenon mentioned in proposition q. In other words, in correspondence with Stern’s definition, the transcendental premise of a TA asserts “that there is a conceptual or metaphysical connection between the phenomenon mentioned in q and the phenomenon mentioned in p such that the latter is a condition for the possibility or the intelligibility of the former” . Thus to be clear, let us call the given “philosophical phenomenon” apart from controversy and dispute (q), while the necessary precondition for that phenomenon is known as (p).
With that understood, this argument becomes interesting for the following reasons: (1) If the skeptic of the given TA happens to deny or reject the necessary precondition (p) required for the phenomenon (q) then he is caught in a whirl of self-contradiction. The reason for this is because if the skeptic grants the given phenomenon (q) while yet denying that a necessary precondition (p) exists for that given phenomenon then he is being incoherent in his affirmation of (q).
An exemplified form of this structure can be found in Descartes’ argument for the existence of himself:
- (C1) I am thinking.
- (C2) It is necessary that: If I do not exist, then I am not thinking.
- (C3) So, I exist.
By virtue of deductive logic, it is absolutely necessary that if (C1) and (C2) are true propositions, then (C3) follows and is also true. The given phenomenon of the argument being that “I am thinking”, while the necessary precondition is that “I exist.” However, according to (C2), if “I do not exist,” (~p), then it is the case that “I am not thinking” (~q). However, it is false that “I am not thinking”, therefore, (C3): I exist.
As noted by Choi, there are three phenomenon’s mostly appealed to in such cases of TAs: logic, science, and objective moral standards. According to Bahnsen’s version of the TA, if the existence of God – who happens to be the ontological foundation of truth – is a negative such proposition (i.e., “God does not exist”), then logic, science, and objective moral standards would be impossible if the necessary precondition of his existence were eliminated. We can structure Bahnsen’s argument as follows with logic as our given phenomenon:
- (TA1) Logic.
- (TA2) It is necessary that: if God does not exist, then not-logic
- (TA3) So, God exists.
The issue in the structure of this argument is that Bahnsen is arguing from the Christian conception of theism, and thus the above argument is incomplete. It should be noted that it is Bahnsen’s position that “we can prove the existence of God from the impossibility of the contrary. The transcendental proof for God’s existence is that without Him it is impossible to prove anything” . Bahnsen in his argument goes on to say:
The laws of logic are not conventional or sociological. I would say the laws of logic have a transcendental necessity about them. They are universal; they are invariant, and they are not material in nature. And if they are not that, then I’d like to know, in an atheist universe, how it is possible to have laws in the first place. And secondly, how it is possible to justify those laws? 
Thus, a reconstructed argument from Bahnsen’s presuppositional basis could be the following:
- (1) There is a rational justification for the laws of logic.
- (2) It is necessary that: if Christian theism is false, then there is no rational justification for the laws of logic.
However, in respect to (2) Bahnsen distinguishes between the justifications of the laws of logic as a priori, a posteriori or mere conventions of human thought. Thence, the necessary preconditions for the given phenomenon of (1) would have to also be reconstructed in full:
- (2a) If there is a non-Christian theistic way to justify the laws of logic, then it will be either the a priori way or the a posteriori way or the conventionalist way.
- (2b) Neither the a priori way nor the a posteriori way nor the conventionalist way will justify the laws of logic.
- (2c) So, there is no non-Christian theistic way to justify the laws of logic.
Referring back to the general structure of TAs, we can form another proposition that could categorize the above argument so to say that:
- (2d’) Necessarily: if there is a rational justification for the laws of logic, then it will be either Christian theistic or non-Christian theistic.
Hence, the basis of (2) might be the conjunction of the other premises (2a)-(2c) and its sister premise (2d’). Unfortunately, with that conjunction we have a problem. Even if we collectively took (2a)-(2c) and (2d’) we wouldn’t necessarily get the conclusion of (2). The reason for this is that the necessary proposition (2) doesn’t follow from the two contingent premises (2a) and (2b). Sean Choi (2007) thence proposes that we turn both premises into necessary ones (i.e., modal propositions):
- (2a’) It is necessary that: if there is a non-Christian theistic way to justify the laws of logic, then it will be either the a priori way or the a posteriori way or the conventionalist way.
- (2b’) It is necessary that: neither the a priori way nor the a posteriori way nor the conventionalist way will justify the laws of logic.
The deduction of (2a’) and (2b’) leads to the necessary conclusion of (2c’): “Therefore, it is necessary that there is no non-Christian theistic way to justify the laws of logic.”
Therefore, our initial premise (2) is valid and thus Christian theism is true.
-  An audio recording of this debate can be found at http://www.youtube.com/watch?v=ZLZdOGCE5KQ
-  A transcript of the debate can be found on PDF at http://www.bellevuechristian.org/faculty/dribera/htdocs/PDFs/Apol_Bahnsen_Stein_Debate_Transcript.pdf
-  Transcendental Arguments: Problems and Prospects, ed. Robert Stern (Clarendon Press: 1999) pp. 3-5
-  Sean Choi, The Transcendental Argument in Reasons for Faith, ed. Norman Geisler and Chad Meister (Crossway Books: 2007) p. 233
-  Ibid., p. 234
-  Transcript from http://www.bellevuechristian.org/; p. 5
-  Ibid., p. 15