The Transcendental Argument for God (TAG) is a modern argument for the existence of God popularly supported by Jay Dyer online. TAG differs from more well-known arguments like the Cosmological Argument in taking what might be called a "meta" perspective. It argues from the possibility of argument itself to the existence of God.
Listening to Dyer discuss TAG on his YouTube videos, he uses words like "paradigm", "presuppositions", "assumptions", and "worldview" frequently. This is an indication that TAG is a characteristically modern argument, as opposed to something like Aquinas's Five Ways, which are characteristically classical. To understand what is really going on in TAG, we must first understand some distinctive features of modern philosophy.
Rene Descartes may be, and often is, designated as a convenient dividing line between ancient and modern philosophy. It is not just when he lived that makes this natural (1596-1650), but also the manner in which he approached philosophy. As a young man, Descartes concluded that what he had learned in school - specifically, philosophy in the Scholastic tradition - produced nothing that was not doubtful and uncertain. He resolved to reject that tradition and replace it with a system he believed would produce certainty. This system was his famous method of methodical doubt, which would subject everything to the most searching doubt and accept only that which might survive. The first result of this method was his famous cogito ergo sum - I think therefore I am.
Subsequent philosophers were deeply influenced by Descartes, but not quite in the way he hoped. Descartes thought he had restarted philosophy once and for all on a sure footing and later philosophers would follow his method and expand its results. While those later philosophers agreed with Descartes that the classical dialog of opinion merely resulted in fruitless debate, the lesson they took from Descartes was that they could restart philosophy themselves on whatever grounds seemed reasonable to them. It was not illogical for them to think so. A consequence of Descartes' approach was to divide thought into two realms: The realm based on methodical doubt that produced reliable and certain results, and the realm of thought not founded on that method and therefore capable only of producing uncertain and doubtful results. The thinking of Descartes before he restarted thought with his method of doubt - the time when he concluded that the Scholastic tradition was barren and in which the method of doubt itself was selected - necessarily occurred in that second realm of doubt and uncertainty, the "gray zone" of thought as it were, since it occurred before the invention of methodical doubt. Since by its own lights it was doubtful and uncertain, philosophers were happy to doubt it and felt free to select their own methods on which to reconstruct philosophy.
What followed was, among others, John Locke starting philosophy with his "plain, historical method", David Hume researching the "secret springs and principles, by which the human mind is actuated in its operations" and, most comprehensively, Immanuel Kant defining the categories of human thought in his Critique of Pure Reason. Things proceeded in a similar manner from there, and the long term consequence of Descartes' philosophical revolution is the general conviction that philosophy begins more or less arbitrarily from some set of first principles that cannot themselves be rationally demonstrated. Everyone is free to choose from where he will begin.
This results in philosophical discourse about "worldviews", "presuppositions" and "paradigms." A worldview is your comprehensive view of things that results from the logical development of your presuppositions. Your paradigm is the methodical framework within which your worldview is explored. Since everyone's worldview is constructed from presuppositions that can be neither defended nor refuted, and not everyone's presuppositions are the same, philosophical debate is only possible where the participants can agree on some set of presuppositions from which valid argument can proceed. If agreement cannot be reached, then fruitful debate is not possible. So debates, including debates concerning the existence of God, often start with a preliminary discussion over what set of presuppositions can be agreed on.
This standard procedure TAG claims to transcend by arguing at a "meta" level. The argument is about the presuppositions themselves rather than some set of conclusions from presuppositions. Simply put, in the version deployed by Dyer, it is argued that the self, the fact that words have meaning, and logic itself (among other things) stand in need of justification if philosophical argument is to proceed. Standard philosophical argumentation concerning God typically takes these things for granted and so is never justified as a whole. The TAG philosopher argues that only God as the one and final presupposition can justify the necessary elements to make philosophical argument possible, and therefore God should be the rationally preferred presupposition.
The peculiar form of TAG often confuses and frustrates its opponents, sometimes for good reason. Familiar with starting arguments by agreeing on presuppositions, the TAG opponent is puzzled that the TAG defender won't quickly agree on presuppositions to get the discussion going, but instead wants to argue about the presuppositions themselves. Yet the whole point of presuppositions in modern philosophical discourse is that they cannot be defended or refuted but only assumed. So argument over which presuppositions are better than others is impossible in principle. There is only personal preference based on whatever arbitrary criteria one might choose. Matt Dillahunty makes this point in his debate with Jay Dyer.
Furthermore, among the many things the TAG philosopher claims need justification are the validity of logic itself and whether words truly have meaning. But if such things are doubtful, how can they be used to arrive at reliable philosophical conclusions, including TAG conclusions? The TAG philosopher is like a man in the year 1500 pointing out that the ship I plan to use to sail from England to America is too small and leaky to make the trip, but that he has a much bigger and more seaworthy vessel I may use. He tells me the ship is over in America, so I need only sail over there in my ship to get it, when I can then confidently sail the Atlantic. Of course, if logic is reliable enough to get us to TAG conclusions, whether they be "meta" or otherwise, it is reliable per se. If logic is too leaky and unreliable to be useful in ordinary arguments concerning God, it doesn't magically become sound just because it is used to argue to TAG conclusions.
The interesting thing about TAG, and the reason I started this post discussing Descartes, is to make a point with respect to the modern philosophical project as a whole. Recall that Descartes resolved to embark on his method of methodical doubt because he had concluded that classical philosophical dialog was a fruitless waste of time. He would set philosophy on a sound footing from which it could derive certain results. Instead the history of modern philosophy has been never ending debate concerning just what those sure foundations are. The conclusion often drawn from the never ending debate is that there are in fact no sure foundations for philosophy, only presuppositions. And as a meditation on presuppositions, TAG is a sort of logical endpoint of modern philosophy. It must necessarily operate in the gray zone implied by modern philosophy, that realm of thought that occurs before the proper method and presuppositions have been determined. Therefore its reasoning and conclusions are necessarily suspect according to the foundational principles of the modern philosophical project. TAG claims that its presupposition of God is "better" than other presuppositions, but the only way to establish this is through using the logic and reasoning that TAG claims is unjustified as part of its premises.
There is only one way forward at this point: Question the foundations of the modern philosophical project itself, i.e. that the classical dialog of opinion is a fruitless waste of time. Since modern philosophy starts with doubting things, why not doubt that?
