My version is: “Think about it well before getting married”.
vs. the version of GPT4:
The phrase “γαμεῖν μέλλε” can be translated as:
“Intend to marry.”
or
“Plan to marry.”
This is an interesting case because between my skeptical interpretation and GPT4’s gung-ho version the original Greek seems like a double-edged oracle that can be justified later no matter whether the marriage turns out to be good or bad. Apart from being naturally skeptical of marriage, my version was influenced by the other Greek maxims about marriage I recall like “The unmarried man has no problems” or “A man who marries when poor is thrice cursed”.
γαμεῖν μέλλε is best understood as “Put off marrying.”
And ϕρόνει θνητά, another of these pithy “Delphic” injunctions, is “Think mortal thoughts”, not so much in the sense of “Contemplate mortality” but more as a warning. Remember you’re only a mortal: Don’t get ideas above your station or you’re asking to get divinely zapped.
Sosiadas takes the next item in his “injunctions of the Seven Sages” list from Diogenes Laertius: καιρὸν γνῶθι, which is attributed there to Pittacus.
I think γαμεῖν μέλλε may be a condensation of a similar bit of advice also recorded in Diogenes Laertius, attributed to Plato: ἐρωτηθεὶς ποίῳ καιρῷ δεῖ γαμεῖν, ἔφη, ‘τοὺς μὲν νέους μηδέπω, τοὺς δὲ πρεσβυτέρους μηδέποτε.’ [That one’s actually worthy of a sage, imo.]
Sosiadas’ Seven Sages also gave us Γάμους κράτει and Γυναικὸς ἄρχε. I guess that first one must be accusative of respect, “conquer in marriage”.
μέλλε as an injunction overwhelmingly seems to come with μή. Enough that this is a very unusual example. The other version of Sosiadas list in TLG (must be the one from the codices?) had γαμεῖν μέλλων καιρὸν γνῶθι, which is obviously wrong, but shows someone somewhen had trouble with γαμεῖν μέλλε.
The meaning of μέλλω is a bit tricky. The basic meaning of the verb seems to be “to be about to”, “to be destined to”, but with γαμεῖν μέλλε it has a derivative sense, which LSJ renders “to be always going to do without ever doing; hence, delay, put off”. Notice that μέλλε is not aorist imperative but present imperative, implying a durative or repetitive process (“keep being about to”).
In γαμεῖν μέλλων καιρὸν γνῶθι we’re dealing with the “basic” meaning; I would translate this “if you’re going to marry, know the right moment [to do it]”.
“Delay, put off” is the gloss, but not the usage: this is the only instance in the Greek corpus, out of 100 or so, where we have imperative μέλλε without a negative. Once you’ve separated out the Epic/poetic occurrences of indicative μέλλε, it’s always μὴ μέλλε or μηδὲν μέλλε or μήκετι μέλλε, etc., except this one time.
Just going by the two digital versions, and having not seen an apparatus for this, it looks as if the editors have fixed the “γαμεῖν μέλλων καιρὸν γνῶθι” to get our current text. That μέλλων version is clearly wrong because subsumes the Diogenes Laertius quote and is out of place coming in this list of short commands and is insipid compared to the rest of the list. But the fix, γαμεῖν μέλλε without that negative, is absolutely unique.