Covenantal apologists frequently encounter an objection in their own mind if it is not raised by someone else in the form of the question, “What exactly is it that we presuppose?”
Perhaps it is God who is presupposed, but then God as divorced from His Word is a concept without Christian content.
Perhaps it is Scripture which is presupposed, but then Scripture as divorced from its Author is a document without authority.
So both of the above must be presupposed, but is that enough? Not if we are to avoid an implicit disconnect between the two. Not if we are to avoid an adherence to solo scriptura.
Perhaps it is a particular doctrine(s) which is presupposed, but then doctrine divorced from God and Scripture is mere human opinion.
All of the above are, and must be, presupposed by the covenantal apologist. They are inseparable constituent parts of the Christian worldview. It is the Christian worldview which is presupposed with all of its respective claims to authority, content, and derivations thereof.
Consider TAG, the Transcendental Argument for God. This label is really a bit of a misnomer, for the aforementioned argument is named what it is only as a matter of emphasis. The argument in question is for the Christian worldview as a whole and in principle, and not for some abstract piece of it. Of course God, Scripture, and any other doctrine in the Christian worldview will be argued for transcendentally. A transcendental argument is the “only argument that holds water” (Cornelius Van Til) with regard to any of the aforementioned Christian tenets.
Enter Greg Bahnsen’s ‘sin’: Those who are not familiar with his wider body of work will assume from his inordinate amount of emphasis upon the existence of God and localized, more analytic style argumentation used in his debate with, for example, Gordon Stein that the presuppositionalist argument is ‘TAG’ and that, quite frankly, it does not work from Scripture or demonstrate anything with respect to other theistic worldviews. Bahnsen’s big three of logic, science, and morality have become the warp and woof of presuppositional apologetics. As his argument is stretched further through various exercises focusing upon the form of the argument the content of the argument gets lost. So Van Til’s primary focus argumentatively speaking was upon the ontological Trinity, but one never hears of such a thing in Bahnsen’s debates, and one certainly never hears of such a thing in the vast majority of Bahnsen’s followers. They have essentially become Thomists.
The Christian worldview as a whole must be set over against its antithetical competitors just as Scripture, Van Til, and Bahnsen all taught, whether or not they were consistent in the application of said teaching.