I don’t think I’ve ever seen Sapphonis, which looks pretty grotesque to me. Does any Latin author ever use it, or is it a fake form by false analogy with Juno? Sapphūs correctly renders the regular Greek gen. Σαπφοῦς, declined like Πειθώ.
Sappho ūs, f. FORMS: acc. -ō HOR.Carm.
2.13.25; gen. -ūs [Ov.]Ep.Sapph.3; abl. -ō
PLIN.Nat.22.20. A celebrated Greek poetess of Lesbos born c. 612 B.C.
nota sit et -o, (quid enim lasciuius illa?) OV, Ars 3.331;
SEN.Ep.88.37; MART.IO.35.t6; STAT,Silv.5.3.155; (of a
statue) -o quae sublata de prytanio est CIc.Ver.4.I26.
Where did you look it up. Not the infamous wiktionary I hope.
Quite so. Consistently the Greek declensional forms. But some Greek 3rd-decl. forms can be troublesome even in Greek, and it’s understandable if Latin writers sometimes assimilated to more familiar declensions. Καλυψώ is analogous with Σαπφώ, but Calypsonis is firmly attested! Still, I’m inclined to stick with “pretty grotesque” for Sapphonis.
Michael’s grotesque Sapphonis shows up a few times in neo-Latin, such as in the Patriologia Graeca Tomus IX Articulus VI, "Sic Plutarchus refert: “Sane musis consecratam fuisse roseam coronam memini me legere in Sapphonis versibus…”
If -us is a proper genitive singular for “Sappho” (and if there are other possibilities), not to mention the other cases, I’m afraid to ask how “Io” should be declined!
Sapphus (long u, Gk. -οῦς) is indeed the proper gen.sing. for Sappho, and similarly with Io, and e.g. Calypso.
Nom. is of course -o (long o). And so is acc., as it happens. The declension is Greek, declining like πειθώ (acc. πειθώ).
And there’s nothing exceptional about Io: nom. and acc. both Io (both vowels long). The Oxford Latin Dictionary, reporting variably Io and Ion for the accusative in Ovid, is misleading: it always comes at verse end, and should in all instances be Io, like the Greek.
(“Why should I mention Io? Why indeed?” If anyone is unacquainted with A.E. Housman’s “Fragment of a Greek Tragedy,” you’re in for a treat.)
Old Latin, e.g. Pacuvius, Andronicus, Plautus, latinizes the Greek forms by assimilating them to Lat. 3rd decl. (hence acc. -onem, gen. -onis, dat. -oni), and so do some later prose writers, but the more sophisticated Augustan poets prefer the conventionally transliterated Greek forms.
The trick is to not approach all this as an arbitrary collection of discrete data and different declensions but to make sense of it all as a system, not a perfectly uniform one to be sure, but a comprehensively intelligible one. We see that Greek names in Latin can either be latinized (as in archaic Latin) or not (as in Augustan poetry).