In Augustine's Confessions, book 3, chapter 4, he writes:
et usitato iam discendi ordine perveneram in librum cuiusdam Ciceronis (source)
Henry Chadwick translates the bolded phrase as "a certain Cicero" and writes:
'A certain Cicero' might seem cold and distant were it not that the same idiom is used for the apostle Paul [...] i.e. it is a rhetorical convention of the time. (source)
However, the example he gives of Paul seems different to me:
ait enim quidam servus tuus (book 12, chapter 15)
Here, it's "a certain servant," and we only know that he's referring to Paul because he proceeds to quote one of Paul's letters.
That is, "a certain Cicero" seems very different than "a certain servant," since "Cicero" can refer to only one person, while the "servant" by itself is inherently vague.
So, my questions. First, is Chadwick correct in saying that "'a certain Cicero'" was a "common rhetorical convention of the time"? If so, was it also common in Classical Latin, or was it something more associated with Augustine's time?
Second, is Chadwick's implication correct, that quidam used in this way could communicate notoriety or respect?
I'd love to see some examples of this usage from the Classical period that back up Chadwick's understanding of this text.