Some sources mention a genitive singular alius, but I've also seen aliae. And I don't recall seeing a dative singular ali, but neither do I remember alio. I think several forms exist, including even suppletive forms like alterius. What would be standard for Cicero?
@quid I rejected your edit by mistake, my apologies. If you would resuggest it, I will accept it.– Cerberus ♦Sep 22, 2016 at 21:13
Lateinische Grammatik (Leumann, Hofman and Szantyr 1977) argues that
"Im Genetiv ist -īus die Standardform der Endung, sie gilt für Plautus und für die klassische Prosa verbindlich. In metrischen Texten bestehen zwei Nebenformen" (Para 376B2a, p. 479) [emphasis mine - Alex B.]
They also add that "Einigermassen häufig sind nur gen. -i und dat. fem. -ae" (p. 480). They admit that the evidence is shaky, cf. "manche Zeugnisse sind unsicher."
Varro, De Lingua Latina 9.62 alii generis
Plautus, Capt. 306: qui imperare insueram, nunc alterius imperio obsequor. [GEN]
Plautus, Bacch. 462: erum ingenium plus triginta annis maiust quam alteri. [DAT]
Here's a screenshot of the OLD entry.
Note that the OLD lexicographers mention that alterius is sometimes used instead of alius.GEN.SG For more elucidating examples/information, we need to look it up in TLL.
Bennett gives gen. alterius, dat. aliī. Allen and Greenough list alius among the adjectives that "have the Genitive Singular in -īus and the Dative in -ī in all genders", implying alīus, aliī, but add in notes that "Instead of alīus, alterīus is commonly used" and that "The regular genitive and dative forms (as in bonus) are sometimes found in some of these words: as, genitive and dative feminine, aliae; dative masculine, aliō". These possibilities presumably reflect Ciceronian and general Classical usage; it's hard to verify this with a search, though, because all the variants happen to be ambiguous with other case forms.
Bennett (of Cornell) indeed observes that [alterius] "is practically always used instead of 'alius' in the genitive". In the UK our standard grammar is that of Kennedy, who gives only 'alius'. Strictly, alter(ius) refers solely to one of two and its substitution for alius is technically illiterate: however, this is often excused on the grounds that nominative alius is frequently, if inelegantly, used where a stylist would opt for alter. The alternative usages seldom cause confusion. Sep 16, 2016 at 10:45
@TomCotton, "technically illiterate" is a little harsh I think... It's a standard usage in Cicero for example, and I wouldn't want to call him illiterate.– TKRSep 16, 2016 at 15:41
yes, I agree, though 'technically' was intended to exonerate the (putative?) illiteracy. This is the kind of thing that just happens in everyday usage and is scarcely to be condemned. Sep 16, 2016 at 16:52
Gildersleeve and Lodge, §76.r1: The Gen. alīus is very rare, and as a possessive its place is usually taken by alienus.
§76.r2: …usually make the Dat. Sing. in -ī … Alī is found in early Latin for aliī.
1Welcome! I've taken the liberty of linking to an online edition of this grammar. Thanks for this answer! Sep 16, 2016 at 11:32
I should have realised that there was one around – thank you for the improvement! Sep 16, 2016 at 11:42