I couldn't sleep on Friday night, so to let Amy catch some Z's I slipped into the study which is next door to our bedroom. I found Goodspeed & Colwell's A Greek Papyrus Reader on the shelf and figured I'd scan through it to see if I could find any interesting instances of non-negative αλλα in papyri.

Boy, howdy did I find one. Check out P.Oslo ii.55. Greek text is from Perseus; translation is from APIS.

Διογένης Πυθαγόρᾳ τῷ ἀδελφῷ χαίρειν.
ἴσθι Θέωνα τὸν παράδοξον τὸν ἀναδιδόντα σοι ταῦτά μου τὰ γράμματα οἰκεῖόν μου ὄντα καὶ σχέσιν ἀδελφικὴν ἔχοντα πρός με. καλῶς οὖν ποιήσεις, ἄδελφε, τοῦτον ὑποδεξάμενος ὡς ἂν ἐμέ. ἀλλὰ καὶ τόπον ἐπιτήδειον αὐτῷ ἀπὸ ποδὸς ἐξηρτισμένον παράσχες, ἀλλ᾽ ἵνα ἐλθὼν μαρτυρήσῃ μοι τὰ τῆς προαιρέσεώς σου.
Πυθαγόρᾳ βουλευτῇ [ ϝαξ. ]

Diogenes to his brother Pythagoras, greeting.
Know that Theon, the extraordinary person who is handing you this letter, is a close friend of mine and has a brotherly relation to me. You would do well, dear brother, to receive him as you would me. Prepare a room as well as you can and let him have it, so that he can bear witness to me about your disposition.
Verso:;To Pythagoras, councillor.

There are two (!!) non-negative αλλα in this short letter, and the translation seemingly skips over them both. So what are these instances doing?

As I've read grammars, monographs, etc. and evaluated instances of αλλα in the NT and Apostolic Fathers, my basic approach in examining them has become twofold: First, I consider αλλα to mark some sort of contrast (or 'discontinuity', as Porter & O'Donnell would call it), the degree of contrast is provided by surrounding context; second, there is usually some correction or replacement going on with the contrasted items. I'm still working on this, but that's about as simple as I can boil it down right now.

[NB: At this point, I should make clear that I'm still thinking through this example; the below is me writing trying to apply things I've noticed to this example to see if they work. These things may change. —RB]

Goodspeed and Colwell (A Greek Papyrus Reader, p. 10, item 19) title this letter “Letter of Recommendation”, and that is what it is. The sender is providing a recommendation of the carrier, so that the carrier will be treated well by the letter recipient. Goodspeed and Colwell summarize the letter thusly: “Diogenes urges his brother Pythagoras to receive the admirable Theon as though he were Diogenes himself.” (Goodspeed & Colwell, 10).

In the letter, the first αλλα is a hinge within the paragraph, the two items that are being contrasted involve the status of the carrier, Theon. After introducing Theon as a friend who is as close as if he were a brother, Diogenes urges Pythagoras to “receive [Theon] as you would me”. He is to receive his own room, apportioned as well as possible. Pythagoras is not simply to perceive Theon as if he were Diogenes, his actions are to confirm this by preparing a place for Theon. The contrast is between receiving Theon (ὑποδεξάμενος) and furnishing a well-apportioned room for him (ἐξηρτισμένον). The correction/replacement is in the unstated expectation that Pythagoras is to do more for Theon than he would do otherwise. Instead of treating him as a visitor, he is to treat him as a brother, both in word and deed.

From this comes the second αλλα, this in conjunction with a ινα clause. This clause makes Diogenes’ expectations explicit: Treat Theon well, for he will report to me how you are doing. The translation of προαίρεσις as “disposition” is curious. LSJ provide a general definition of “choosing one thing before another” (LSJ 1466) but further delineate nine senses, one of which (#7) is “character, reputation” and another (#8) “devotion, affection, goodwill”. The correction is in the expectation. Diogenes purposes to ensure Theon is treated well, and underscores this by making explicit that Theon will report back regarding Pythagoras’ hospitality.

Diogenes' purpose for writing the letter is to ensure that Theon is treated well by Pythagoras. The use of αλλα in the second half of the letter helps Diogenes achieve this purpose, helping Pythagoras to understand the importance of treating his guest not simply properly but as if he were his brother Diogenes himself.

There is a progression in these statements tied together with αλλα: Don't just receive Theon, but provide him a room as you would do for me. And not only that, but know that he will report back to me how you have done in this matter. The important bit for Pythagoras: Make sure the report back to Diogenes is a good one.