The 2nd Declension Neuter endings are:
Nom: -um
Acc: -um
Nom: -a
Gen: -ōrum
Dat: -īs
Acc: -a
Abl: -īs

With a word such as auxilium (meaning help, aid), which is 2nd declension neuter, why does the i from the base (auxili) get dropped in the genitive singular so that the genitive singular form would be auxilī instead of auxiliī? The base auxili remains for all the other forms... For example, the dative and ablative plurals are both iudiciīs, keeping the double -iī at the end of the word.

Maybe there are some Latin authors who did write the genitive singular form with the double -iī, but based on everything I've learned/seen, it's typical to only have in the genitive singular. Does this hold for both classic and modern Latin, or just one of the types?


A full table of "standard" (post-Augustan) -ius/-ium endings would be:

    M SG    M PL    N SG    N PL
NOM -ius    -iī     -ium    -ia
GEN -iī     -iōrum  -iī     -iōrum
DAT -iō     -iīs    -iō     -iīs
ACC -ium    -iōs    -ium    -ia
ABL -iō     -iīs    -iō     -iīs
VOC -ī      -iī     -ium    -ia

(O tempora! O mores! Why must upstanding citizens be disallowed from having proper <table>s? Something something Catalina)

In earlier Latin, the genitive singular for both masculine and neuter was . In other words, you would always see auxilī instead of auxiliī, and fīlī instead of fīliī. But during the Augustan period authors stopped treating -i- nouns specially, and this form was regularized to -iī. From the link below, "the genitive in -iī occurs once in Virgil, and constantly in Ovid, but was probably unknown to Cicero."

For (a little bit) more information, see Allen and Greenough section 49b.


Here’s a summary of what most authoritative Latin grammars say on the genitive singular ending of –io stems (Weiss 2009/2011: 222-223; Leumann 1977: 424-425; Sihler ). For the sake of simplicity and consistency, in my answer I use the periodization of Latin as used in Weiss (which is different from, for instance, Clackson and Horrocks or Meiser). Weiss has a beautiful quote from Wright 2003, "All periodizations are, of course, administrative fantasies."

In Very Old Latin (6th-3rd centuries BCE), the genitive singular ending was –osio (VALESIOSIO in Lapis Satricanus and perhaps TITOIO, see chapter 4 in Bakkum 2009 for a more detailed discussion).

In Old Latin (3rd-2nd centuries BCE), the genitive singular ending was only –ī, from *-ihx (cf. Leumann “im Altlatein nur –ī, nicht –iī”). This ending was contracted from -iī. This contracted form can be found, for instance, in Plautus (e.g. beneficī). Note this ending is thematic. Also, in masculine nouns the contraction did not affect stress position, thus gen.sg. Valéri.

Penny 2011 writes that "the Latin evidence does not allow more than speculation about the original function and distribution of the two endings" [i.e. -osio and -ī, Alex B.].

Later, due to analogical leveling, it was restored, first in adjectives and later in nouns; so, in Classical Latin (1st century BCE- 3rd/4th centuries CE), it was –iī as well as -i (cf. Leumann “In späterer Zeit aber gilt –iī als die richtiger Form” though).

Such forms are found in Andronicus (e.g. Saturni, uerbi), Vergil (e.g. fluviī), Propertius (imperiī, ingeniī) etc.

Leumann also mentions that "Das scheinbar regelmäßige -iī bei io-Stämmen, das schon Varro empfiehlt" and Varro lived in 116-27 BC. Tronskii 1960 adds that the -ī form was still used in the so called post-Augustan Latin (Silver Latin); he argues that Horace (i.e. Augustan) and Persius (post-Augustan) don't use the -iī genitive singular. So, there was a lot of variation.

Even in Augustus' Res Gestae (1: 22) we can find "magister conlegii" etc. The point is that all these changes did not happen overnight. Obviously, there was no decree making all Latin writers use the -iī after Augustus death.

Interestingly, re: auxilii - and the reliability of Latin corpora brought up here in some comments, Leumann remarks that

“Für Cicero und Caesar (auxilii Gall. 1, 31, 14 usw.) ist auf die handschriftliche Überlieferung kein Verlass” - basically, we don't really know which form they used (at least, with poetry there is metrical evidence).

I will add results of my corpus research later. For instance, I searched LASLA for Gr.Cat: Noun, Gr.Sub.Cat: 2nd decl., Case: Genitive, Number: Singular and it returned 16438 results - which I have to analyze manually now.

  • 2
    I'm still having trouble cutting through the thicket here, but this definitely gets my vote for sources. I still see some conflict between the accepted answer's contention (-ii used in Augustan period) and this one: are you sure (in context) that "spaeterer" refers to "Classical Latin" and not, say, Silver Age Latin? Also, do you know anything about the relative distribution of usage in classical authors?
    – brianpck
    Nov 21 '16 at 13:24
  • @brianpck I tried to answer some of your questions. Something to remember: not all classicists use such terms as Silver Latin etc.
    – Alex B.
    Nov 21 '16 at 19:14
  • 1
    @brianpck To pick up on what Alex B. said, Classical Latin encompasses both Golden Age and Silver Age Latin, to the former of which I think you were referring.
    – cmw
    Nov 21 '16 at 19:40

Edgar H. Sturtevant's dissertation "Contraction in the case forms of the Latin io- and ia stems, and of deus, is, and idem" (1902) seems to have some relevant info, although I don't know if more has been discovered since then.

Contraction in the genitive singular

Sturtevant starts out by summarizing the genitive singular forms: he says that in early Latin, substantives always used contracted genitive singular forms in -i, while adjectives used -ii. Later on -ii became usual for substantives as well, although -i was still used in some proper nouns (p. 3*).

I haven't used macrons here because Sturtevant doesn't, but these forms would have normally been pronounced and -ĭī.

Alex B.'s answer provides more detailed information about the use of contracted forms in for the genitive singular of nouns with stems ending in -io-.

Contraction in plural forms

Apparently, contraction probably also occurred in the masculine nominative plural () and the dative/ablative plural (-īs) for at least some words, in some time periods, but the issue is rather complicated because the contraction may have been reversed by analogy. Also, spelling variants may not have always corresponded to pronunciation variants, due to either mis-spellings (e.g. leaving out a letter) or conservative spellings (such as -iei, ieis, which Sturtevant argues could represent the pronunciations -ī, -īs) (p. 8*). The part about contraction in the nominative plural is only relevant for masculine nouns, since neuters get the suffix -a, but I'd imagine masculine and neuter nouns behaved similarly in the dative/ablative plural.

Sturtevant says that Plautus probably only used uncontracted forms of the masculine nominative plural and the dative/ablative plural, and references a theory of Klotz's that explains away apparent contracted versions of these forms in Plautus (p. 4*). According to Sturtevant, these forms would have contained something like [i.eː] in Plautus's time. I'm using [eː] as a broad IPA transcription of a long vowel that was closer than ē but opener than ī: Sturtevant mentions that a vowel with this quality is thought to have been the intermediate result of the coalescence (in non-initial syllables) of the etymological diphthongs oi and ai, before their reflexes merged into ī as /iː/ (p. 6*). The presence of [eː] in the sound system of Latin of this time period is thought to be the original reason for the use of the digraph "ei", although after [eː] merged into /iː/, the digraph "ei" came to be just an alternative (eventually, archaic) spelling for "i".

Sturtevant says that as far as he knows, the earliest inscriptional examples of contraction in these plural forms occur on the Sententia Minuciorum, dated "a. u. c. 637": i.e., 117 BC (p. 6*).

*Note: The linked scan has two systems of page numbers; I reference the top ones.


Neuters of the second declension ending -ium always have the gen. sing. in -I, never -ii. This is unlike the masculines in -ius (filius, genius etc. and most proper names), which can have either -i or -ii.

The form that you encounter is a question of usage. Writers of the golden (i.e. the best) age, and especially poets, use only the contracted form in -i, which explains what you have seen. Elsewhere, the two forms can appear haphazardly — but very seldom are neuters seen to end in anything but the single -i.

This is clearly explained in Kennedy's Revised Latin Primer in the notes to Arts. 38b and 71.

  • 2
    This is simply incorrect: The Packhum corpus has 102 examples of auxilii and only 29 instances of auxili.
    – brianpck
    Nov 18 '16 at 17:34
  • @brianpck Interesting. How reliable is your source Packhum? From where does it draw its authority for the texts as it quotes them? My own Oxford Classical Texts disagree with the first six examples that I have looked at. I gave an answer as I have long believed it, and checking in Kennedy I find agreement with what I have stated.
    – Tom Cotton
    Nov 18 '16 at 17:59
  • 2
    Can you include some of those sources in your answer? Here are Packhum's sources, though a quick check on one quote from Cicero in Perseus, which uses the Teubner edition, appears to agree. This Oxford version of De Bello Gallico also seems to confirm the double-i. I don't have access to the physical books to confirm this now, though.
    – brianpck
    Nov 18 '16 at 18:13
  • 1
    Perhaps you'd like to reconsider your criticism in light of the other answers. I'm unsure which sources you have asked for: if you mean Kennedy, it is in the notes to articles 35b and 71. Your trust in corpora compiled from already edited texts is quite touching.
    – Tom Cotton
    Nov 19 '16 at 10:41
  • 2
    Three issues: (1) There is no note relevant to this topic in article 71, (2) Art. 35 states that authors of the "best age"--especially poets--use the contract form, which is radically different from your two claims that (a) there is a distinction between neuter and masculine contraction and (b) the aforesaid authors "only" use this form, and (3) currently we are pitting the authority of an elementary grammar against concrete loci, which I admit can be flawed, but which I hope you will contest with actual citations, not unmerited condescension.
    – brianpck
    Nov 20 '16 at 0:23

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