In Development 1.3.5, Newman draws an inference: “If the Christian doctrine, as originally taught, admits of true and important developments, as was argued in the foregoing Section, this is a strong antecedent argument in favour of a provision in the Dispensation for putting a seal of authority upon those developments.” That is, Christians have good reason to expect “the appointment in that scheme of an external authority to decide upon [doctrinal developments], thereby separating them from the mass of mere human speculation, extravagance, corruption, and error, in and out of which they grow. This is the doctrine of the infallibility of the Church” (1.3.4).
But Newman then considers an objection to this view which had once raised in his Prophetical Office of the Church: doesn’t the appeal to an infallible magisterium to certify true developments of Scripture require in turn an infallible interpreter to certify true instances of magisterial teaching? And doesn’t that interpreter need one in turn? (1.3.6) Doesn’t this leave us, like Carroll’s Achilles, locked in the Sisyphean task of providing warrants for our warrants for our warrants, ad infinitum?
Newman first grants the qualification that our reception of an authority as infallible is only probable; we (and presumably this includes even the bishops in council themselves) don’t have infallible grounds for ascertaining the infallibility of the bishops in council. But, he insists, “a probable infallibility is a probable gift of never erring; a reception of the doctrine of a probable infallibility is faith and obedience towards a person founded on the probability of his never erring in his declarations or commands” (1.3.6). If it’s necessarily true that p, does that mean that it’s also necessarily true that I know that p? Of course not! Modality in the order of being has nothing to do with modality in the order of knowing.
The objection treats the expectation of an infallible interpreter for an infallible text as essentially epistemic, a bid to put an end to all uncertainty. Newman clarifies that his interest in this expectation is practical, one might almost say pastoral: grant that divine revelation is the definitive means by which the LORD communicates his will for us (Newman isn’t arguing for this point; we’d need a different set of arguments to deal with objections to it); if so, then that means that the LORD expects Scripture to be effective in communicating that will, to be effective in training us in how to be in right relationship with him, with ourselves, and with our fellow creatures. But in point of fact, Newman insists, Scripture doesn’t do this on its own — interpreted according to “private judgment,” Scripture doesn’t at all clearly treat points that later came to be seen as crucially important (the licitness of re-baptism, the intermediate state of the soul after death, the fate of unbaptized infants), and even on questions about which it arguably speaks quite clearly (the divinity of Christ), it provides prima facie support for a bewildering variety of heresy (as the history of doctrine makes plain). So, if these “developments” of Scripture are as important and as under-determined as they appear to be, then shouldn’t we expect that the LORD would provide an instrument for settling the Church’s mind about them? Shouldn’t we expect, that is, a magisterium whose authority and finality is proportioned to the authority and finality of the teachings which it is to interpret? (There’s an analogy to be drawn here between the Church’s gradual discernment of its authority as authoritative interpreter of the depositum fidei, and the Supreme Court’s gradual — though admittedly quicker — discernment of its authority as final arbiter over the meaning of the Constitution (cf. Marbury v. Madison ).
The interpretive action of the Church in clarifying Scripture’s ambiguities and entailments does not evacuate the need for “personal judgment” on the part of the recipient, nor obviate all further interpretation; rather, it “limits” the scope for that judgment and that interpretation, in a manner precisely analogous to the limitations that Scripture by its very nature imposes on them: “it limits their range, [but] it preserves intact their probationary character; we are tried as really, though not on so large a field” (1.3.8).
I’ll wrap this up with one of Newman’s characteristically pregnant analogies: “Preservation is involved in the idea of creation…As creation argues continual governance, so are Apostles harbingers of Popes” (1.3.10).