Cardinal, now Pope, Joseph Ratzinger, while commenting on the documents of Vatican II (article nine of Dei verbum), stated that “no one is seriously able to maintain that there is a proof in Scripture for every catholic doctrine.” See Joseph Ratzinger’s “The Transmission of Divine Revelation” in Herbert Vorgrimler, ed., Commentary on the Documents of Vatican II (New York: Herder and Herder, 1969), Vol. 3, p. 195.
When I quoted this some time ago (here), Mr. Waltz commented: “As for David’s isolated quote, he [Ratzinger] was dealing with interpretation (formal sufficiency) and not simply material sufficiency. David King clearly misspoke; but you know, everyone makes mistakes, and the bulk of his work/s should be judged on their OVERALL merit and content.” (link - that page seems to have been removed - here's a cached page containing the quotation)
What I suspected then, concerning Ratzinger's inconsistency on the question of material sufficiency, is now cleared up (I think) in the work, Joseph Cardinal Ratzinger, now Pope Benedict XVI, God’s Word, Scripture—Tradition—Office, Peter Hünermann and Thomas Söding, eds., Henry Taylor, trans. (San Francisco: Ignatius Press, 2005). Some of this material has been reworked from an earlier publication, namely, Karl Rahner and Joseph Ratzinger, Revelation and Tradition (New York: Herder and Herder, 1966).
Now, to be sure, I have always thought that our Roman disputants are themselves inconsistent on their affirmation of the material sufficiency of Scripture. But I think this later work by the man who is now Pope makes it clear that he does not affirm material sufficiency in any positive sense, and I did not (as Mr. Waltz charged) misspeak on this issue. I would encourage any Roman disputants to remain calm, at least until they’ve read the extended quote below.
Cardinal Joseph Ratzinger, now Pope Benedict XVI:
Geiselmann starts from a new interpretation of the Council of Trent’s decrees about the nature of tradition. Trent had established that the truth of the gospel was contained in libris scriptis et sine scripto traditionibus. That was (and is to this day) interpreted as meaning that Scripture does not contain the whole veritas evangelii [truth of the gospel] and that no sola scriptura principle is therefore possible, since part of the truth of revelation reaches us only through tradition. Geiselmann took up the point, already made by others, that the first draft of the text provided the formulation that truth is contained “partim in libris scriptis partim in sine scripto traditionibus”. Here, then, the doctrine of a division of truth into two sources (Scripture and tradition) was clearly articulated. The Council renounced the use of partim—partim, however, and contented itself with the simple conjunction et. Geiselman concludes from this that they had turned away from the idea of a division of truth into two separate sources, or had at least not explicitly defined it. And he further concludes that consequently even a Catholic theologian can argue the material sufficiency of Scripture and can also, as a Catholic, hold the opinion that Holy Scripture transmits a material sola scriptura thoroughly acceptable even for a Catholic—indeed, he believes he can show that this has much the stronger tradition in its favor and that the Council of Trent, likewise, intended to point us in this direction.See Joseph Cardinal Ratzinger, Pope Benedict XVI, God’s Word, Scripture—Tradition—Office, Peter Hünermann and Thomas Söding, eds., Henry Taylor, trans. (San Francisco: Ignatius Press, 2005), pp. 48-51.
It is easy to understand how such a thesis could count on widespread agreement in view of the quite new opportunities for contact between Catholic and Evangelical Christians that it seemed to open up. [Here Ratzinger offers a footnote concerning how he and H. Fries, in another work, gave a survey of everyone who agreed in principle with Geiselmann] I hold it to be quite indisputable that it does indeed represent appreciable progress in objective terms. Nonetheless, as soon as one analyzes it somewhat more closely with respect to both its historical and its factual basis, a whole series of questionable points emerge that make it impossible to stop at that. In the second section, we will attempt a few remarks on the historical side of the problem; meanwhile, we turn directly to the problems of the subject itself, and any investigation of this will probably first of all produce the question: What does “the sufficiency of Scripture” actually mean? Even Geiselmann, as a Catholic theologian, cannot get beyond having to hold fast to Catholic dogmas, and none of them can be obtained by means of sola scriptura—not the early Christian dogmas of the former quinquesaecularis consensus, and still less the new ones of 1854 and 1950. What kind of meaning does talk about “the sufficiency of Scripture” still have, then? Does it not threaten to become a dangerous self-deception, with which we deceive ourselves, first of all, and then others (or perhaps do not in fact deceive them!)? In order to go on maintaining that Scripture contains all revealed truth, on one hand, and, on the other, to maintain that the 1950 dogma [which I pressed on Mr. Waltz repeatedly] is a revealed truth, we would have at least to take refuge in a notion of “sufficiency” so broadly conceived that the word “sufficiency” would lose any serious meaning.
This, however, opens up the second and really decisive question: In concerning ourselves with the idea of the “sufficiency” of Scripture, have we grasped the real problem involved in the concept of tradition at all, or are we lingering over a relatively superficial symptom of an issue that in itself lies much deeper? The introductory reflections from which we started should have made it clear that the answer to this question must clearly be Yes. The question of the sufficiency of Scripture is only a secondary problem within the framework of the far more fundamental decision that we glimpsed a little while ago in the concepts of abusus and auctoritas, and that thus concerns the relationship between the authority of the Church and the authority of Holy Scripture; everything else depends on how we understand that.
To make further progress, it will therefore be necessary to deepen our approach, not being preoccupied with such superficial implications as the sufficiency or insufficiency of Scripture, but presenting as a whole the overall problem of the mode of presence of the revealed word among the faithful. Then we can see that we have to reach beyond the positive sources of Scripture and tradition, to their inner source: the revelation, the living word of God, from which Scripture and tradition both spring and without which neither can be grasped in the importance they have for faith. The question of “Scripture and tradition” remains insoluble so long as it is not expanded to a question of “revelation and tradition” and thereby inserted into the larger context in which it belongs. In what follows, therefore, I should like to unfold the concept of tradition in a positive sense, on the basis of its inner impulse, in thesis form, without going into the details of possible arguments. I do this in the hope that some part of an answer to the Reformers’ question may be found in it and that the whole may thus prove to be a part of a conversation, the necessity of which is being recognized with increasing clarity on both sides.
As he indicated, Ratzinger proceeds to offer another “thesis” than that of Geiselmann and others. Two things are clear, he does not affirm the material sufficiency of Scripture in any positive sense; and if his language is to be understood at all, he thinks that such a formulation misses the bigger point of what he calls “revelation and tradition.”