Cur nullum genus adiectivo "vetus"?

Question

Why doesn't the adjective vetus inflect for gender?*

I checked the etymology and vetus appears to have been inherited from Proto-Indo-European by the usual route. So why is it irregular?

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* _{OK, strictly speaking, it's marked for neuter vs. masculine/feminine (vetus vs. veterem), following the exceptionless pan-Indo-European rule that neuters don't distinguish between nominative and accusative. And the neuter nominative/accusative plural is vetera, following the (pseudo-)rule that the neuter plural is the same as the nominative feminine singular—except that in this case, the nominative feminine singular is vetus.}

Answer 1

My impression is that in this regard, vetus is like the other third-declension adjectives "of one termination", such as fēlīx, atrōx, or -ns present participles. While adjectives like this are fairly uncommon, I don't think they're considered to be irregular just because of the way they (don't) inflect for gender.

I'm not sure what the historical origins of this conjugation pattern are, though, or whether vetus is actually like the other mentioned words from a diachronic perspective. Another oddity about the inflection of vetus, which it doesn't share with fēlīx and atrōx, is that it apparently is declined as a consonant-stem rather than as an i-stem in all forms¹, but I don't know if this is at all related to the way it forms the nominative singular.

András Cser's The nature of phonological conditioning in Latin inflectional allomorphy (2015), which tries to give a synchronic account of Classical Latin inflectional morphology, contains the following footnote:

36. Some adjectives do not mark gender in the singular at all (e.g., vetus ‘old’, audax ‘bold’). More precisely, they only mark gender by using the NomSing form for the neuter accusative (Masc/Fem veterem, audacem vs. Neutr vetus, audax). Note that in these neuter nominative-accusative forms the animate NomSing affix -s appears on adjectives like audax or all the -ns-final participles, which is very unusual from a systemic – and also from an Indo-European – point of view

(p. 24)

The existence of the s~r alternation in vetus, veteris seems to be a sign that that from an etymological perspective, the "s" in the form vetus doesn't necessarily have to be identified as the suffix -s. The Wiktionary entry for the PI etymon "wetos" describes it as a neuter consonant-stem noun, like PI "genos" (the etymon of CL genus, generis).

I don't know enough to say whether Cser's analysis of the morphology of these adjectives (where the "animate NomSing affix -s" is interpreted as appearing in the nominative singular for all three genders) is correct from a synchronic point of view. Kyle Gorman's "Latin Rhotacism for Real" may be relevant, as it tries to give a synchronic account of various phenomena that are traditionally explained in terms of "rhotacism" of s.

De Vaan's entry for this adjective notes "P1.+; Enn. nom.sg. veter", so it looks like a masculine/feminine nominative singular form that was distinct from the neuter did arise at one point.

1. The unusual consonant-stem declension pattern of vetus, and some other adjectives that may show a similar pattern

Third-declension adjectives usually end in -ī in the ablative singular, -ia in the neuter plural, and -ium in the genitive plural, but with vetus we have vetere, vetera, veterum (at least typically; I don't know if any i-stem forms are attested as variants in the classical or pre-classical period). In this regard, its inflection seems to be similar to that of comparative adjectives (which have two terminations in the nominative singular: m/f -ior and n. -ius, and have the abl. singular -iōre, n. plural -iōra and gen. plural -iōrum).

There do seem to be a few more non-comparative third-declension adjectives that are not i-stems, a page from "Introductory Latin" on Louis Ha's website gives the following list of examples (all of one termination): compos, compotis; dives, divitis; particeps, participis; pauper, pauperis; princeps, principis; superstes, superstitis and vetus, veteris. Unlike vetus, many of these seem to lack attested nominative/accusative neuter plural forms in -Ca.

Charles E. Bennett's Latin Grammar gives a similar list, and mentions a complication with regard to dives: apparently no nominative or accusative neuter plural form based on the stem dīvit- is used (e.g. we don't find either *dīvita or *dīvitia; Lewis and Short also agree that forms like this do not occur) but we instead always find the contracted i-stem form dītia (for other forms of the word, it seems the contracted forms like nom. sing. dīs and gen. sing. dītis coexist with the uncontracted forms like gen. sing. dīvitis).

I have also found an old French source (Grammaire de la langue latine, by J. M. Guardia and Justynian Wierzejski, 1875) that says that pauper, along with some other third-declension adjectives of one termination, is defective in the nominative and accusative neuter plural:

Beaucoup d'adjectifs à une seule finale n'ont point les cas de pluriel en a : puber, pauper, sons, suplex, trux, inops, memor, deses, etc., qui ne s'appliquent qu'à une seule personne. Dives fait ditia (et non divita ou divitia).

(My translation: "Many adjectives of one termination do not have the plural cases in -a: [...] etc., which only apply to a person (to one person?). Dives makes ditia (and not divita or divitia).")

(p. 133-134)

I have just read the Allen & Greenough §122 page that you linked to in your answer to the question Are there any indeclinable adjectives?, which mentions inops as an example of an adjective where the non-occurrence of a neuter plural form is just a consequence of the meaning.

Answer 2

vetus, even though being of the "one-ending" adjectival type, is still a unique adjective and, despite a number of solid IE cognates (see de Vaan or Walde-Hofmann), its internal etymology in Latin "remains unexplained to date" (Sihler 1995: 353).

The only hypothesis I am aware of is that originally it was a neuter noun, cf. Leumann et al. 1977: 269:

"Ein Wandel Subst. -> Adj. ist ganz selten und untypisch"

(English translation: The change Noun -> Adjective is rather rare and atypical) or

Walde-Hofmann 1938/2007: "vetus ist neutraler -os-St" or "Formell ist vetus ein adjektiviertes Subst.*u̯etos".

cf. Szantyr and Hoffman 1972/1997:158 ("Lateinische Syntax und Stilistik"):

"Ein Fall der Adjektivierung eines Subst., allerdings anders geartet, liegt auch bei vetus vor; falls formal = gr. έτος (ursprünglich also 'ein Jahr sc. alt'), wäre es zu seiner Bedeutung und adjektivischen Verwendung wahrscheinlich zunächst in Verbundungen mit Worten wie vinum (vgl. die alte Formel bei Varro ling. 6, 21 novum vetus vinum bibo) und morbus gekommen [...]"

Answer 3

Vetus is in fact completely regular: it does inflect for case, number, and gender. It just happens to look the same in the masculine and the feminine.

To quote from this other answer:

Latin has five classes of adjectives, which are generally put into two main groups.

• "First/Second Adjectives"
  • "Normal" adjectives: these take the standard endings for the first and second declensions, and look different in all three genders. Bonus is one of these: bonus, bona, bonum.
  • "Irregular" adjectives: these are the same as the normal ones, except that the masculine genitive and dative singular use the older endings -ius and -ī instead of -ī and -ō. There are only nine of them in the entire language, which are commonly learned with the mnemonic UNUS NAUTA.
• "Third Adjectives": these ones decline like third-declension nouns.
  • One termination: these adjectives look the same in all three genders, like atrox, atrox, atrox. The only gender differences are the standard rules for the neuter (-ia in the plural, accusative matches the nominative). Present participles are in this class.
  • Two terminations: these are the most common "third" adjectives. They have one form in the masculine and feminine, and a different form in the neuter, like omnis, omnis, omne. Comparative adjectives also tend to be in this class, like melior, melior, melius.
  • Three terminations: these are the rarest ones. They have different forms in each different gender, and the masculine always ends in r, such as celer, celeris, celere.

Vetus is an adjective of one termination, which means the masculine, feminine, and neuter look the same in many (but not all!) forms. The cases where they diverge show that there's still agreement, even if it's not visible: the singular accusative veterem versus vetus, and the plural nominative veterēs versus vetera, for instance.