ὦ ἀγαθέ, or the creeping of the philosophical into historiography

Ὁ δὲ Βροῦτος αὐτῷ πάλιν παραστὰς, “Ἴθι, ὦ ἀγαθὲ,” ἔφη, “τοῖς λήροις τούτων χαίρειν φράσας…”

and Brutus was standing with him again saying, “Go my good friend, be done with the non-sense of these people…” (Nic. Aug. 87; Toher trans.)

I read the above and started to fret a little over the vocative ὦ ἀγαθὲ. It felt unfamiliar and maybe an odd translation. Nope. Totally standard translation according to the LSJ:

ὦ ἀγαθέ, my good friend, as a term of gentle remonstrance, Pl.Prt.311a, etc.

Huh, I thought, maybe this is a philosophical thing? Ya sure you betcha! One use in Isaeus. But then lots of Plato and always with Socrates teasing and guiding the other interlocutors to the ‘right’ conclusion away from some ‘preposterous’ one (Republic, Phaedrus, Crito).

Where else does it show up? Well in the mock philosophic dialogue of Athenaeus!

[Bye-the-bye, it’s also all over early Christian writers and has some antecedents in the NT, probably a philosophical influence but not really my area, so I leave it be]

So what I like about this all is that Nicolaus the Peripatetic is bring his vocabulary of Philosophic dialogue into his life of Augustus. BUT, of course, we know that Brutus is deceiving Caesar at this moment! So is Nicolaus constructing ὦ ἀγαθέ as a bit of sophistry? Is Plato playing with sophistic rhetoric when he uses it in his Socratic dialogues?

Interestingly, Appian uses ὦ ἀγαθέ in moralizing discussions between friends deliberating correct action:

στενῆς δὲ τῆς ἐξόδου πάμπαν οὔσης ὁ Βλάτιος ἔφη τῷ Δασίῳ, τοὺς ἄλλους λαθών·
“οὐ σώσεις, ὦ ἀγαθέ, τὴν πατρίδα;”ὃ δὲ καὶ τοῦτ’εὐθὺς ἐκβοήσας ἐμήνυεν. …

As they were going out by a very narrow passage Blatius said to Dasius in a low tone, “Are you not willing to save your country, good sir?” The latter immediately repeated the words in a loud voice… (App. Hann. 45, White trans.)

ἐπανερομένου δὲ τοῦ Κασσίου· “τί δ’, ἂν ἡμᾶς καλῶσιν ὡς στρατηγούς, τί ποιήσομεν, ὦ ἀγαθὲ Βροῦτε ”; “ἀμυνῶ τῇ πατρίδι,”ἔφη, “μέχρι θανάτου.”

Then Cassius asked him further, “What if we are summoned there as praetors, what shall we do then, my good Brutus?” “I will defend my country to the death,” he replied. (App. BC 2.113, White trans)

These instances are so similar that they feel like Appian must have a common model for both. His usage feels much more platonic, that Nicolaus’ sophistic tongue and cheek usage.