Eberhard Busch describes Barth’s approach to theological prolegomena:
he saw the prolegomena as being a first step into the subject-matter itself, bringing about a first clarification of what revelation was and how it was to be spoken of. The prolegomena were concerned “not with the things to be said beforehand, but with the things to be said first.” Or in other words: “Thus in the prolegomena to dogmatics we are concerned with the Word of God as the criterion of dogmatics.” (Karl Barth: His Life and Letters, 213)
Bavinck, interestingly, treats apologetics as an aspect of prolegomena in a similar fashion, folding the discipline into the dogmatic enterprise, not something prior to or outside of it:
Apologetics cannot precede faith and does not attempt a priori to argue the truth of revelation. It assumes the truth and belief in the truth. It does not, as the introductory part or as the foundational science, precede theology and dogmatics. It is itself a theological science through and through, which presupposes the faith and dogmatics and now maintains and defends the dogma against the opposition to which it is exposed. (RD I:515)
Bavinck’s statement is quite consistent with Van Til’s own approach to both theology and apologetics. Van Til was concerned to set a course correction in what he saw in the history of theology, particularly in Aquinas and Old Princeton tradition, where prolegomena in general and apologetics in particular were treated “philosophically” and as a precursor to doing theology. It gave the feel that apologetics has a different starting point than theology, as if prolegomena/apologetics were autonomous disciplines based on another ground than that of theology. Bavinck and Van Til, however, want to make it clear that prolegomena/apologetics, no less than theology, begin at the same place: special revelation. Therefore, prolegomena/apologetics are not separate from dogmatics, but an aspect of dogmatics.
Barth was quite famous for his rejection of apologetics. But his rejection of apologetics was not a rejection of defending the faith as such. What he rejected was a form of apologetics found in the analogia entis of Thomas and—Barth would add—liberal theology. Schleiermacher, and those who walked in his ways, were concerned to ground their defense of the faith and the things that need to be said beforehand in philosophy, reason, and what Barth regarded as “natural theology.” This gave the apologetic endeavor a man-made, or man-centered, orientation. This is why Barth shouted from the rooftops a resounding Nein! to Brunner’s proposal for a recovery of natural theology.
For Barth, then, prolegomena must be founded upon the same grounds as all of dogmatics—God’s revelation witnessed to in his Word. Barth disdained autonomous natural theology and man-centered prolegomena just as Bavinck and Van Til did.
Is there a place of rapprochement between Barth and Bavinck/Van Til?!
Now, to be sure, the agreement between Barth and Bavinck/Van Til does not last long. Barth takes his doctrine of revelation in a very different direction than Bavinck/Van Til did. Almost immediately the two diverge in polar opposite directions. Barth will allow for autonomy, indeed. It won’t be in the area of prolegomena, at least not formally. Yet where he allows for it will affect his prolegomena, whether he realized it or not. He could not keep the proverbial autonomous camel out of the tent once he allowed its nose of biblical studies in. Whereas for Van Til the Scriptures are the revelation of God giving us both the history of special revelation and its interpretation infallibly, Barth allowed the would-be autonomous bible scholar to discern what in Scripture witnesses to revelation and what does not. The Scriptures are the Word of God only insofar as they witness to revelation (i.e., Jesus Christ). Where they do that rightly, there we have the Word of God. But where there is error, there the authors and the text (both being caught up in this fallen world) fail to witness to revelation. And it is up to the autonomous reader to determine the difference.
And so, despite his best efforts to the contrary, natural theology found its way into Barth’s theology after all.