I’m trying to rationalise my way through the deep and dank forest that is the third declension - in particular, how to know when a noun will take -um or -ium in the genitive plural. I’ve looked at one or two sites on the web and in Allen and Greenough (I like the way the latter says “The i-declension was confusing even to the Romans themselves,”) and I’m still a bit confused. I’ve tried to take what I’ve seen and distill it down to the simplest form I can (I’m not that far on in my studies, so simple is good as long as it’s not actively misleading).
Third declension nouns take -um in the genitive plural, unless they are:
A. imparisyllables of the following types
monosyllabic nom sing nouns ending in cons + -s
⁃ ars, artis (f)
⁃ nox, noctis (f)
⁃ os, ossis (n)
⁃ urbs, urbis (f)
exceptions which can take either -um or -ium such as:
⁃ cīvitas, cīvitātis (f)
⁃ parens, parentis (m/f)
exceptions which only take -ium, such as
⁃ līs, lītis (f)
B. parisyllables ending in -es or -is. E.g.
⁃ puppis, puppis (f)
⁃ sitis, sitis (f)
⁃ secūris, secūris (f)
⁃ turris, turris (f)
⁃ tussis, tussis (f)
⁃ nūbes, nūbis (f)
C. neuter nouns whose nom sing ends in -e, -al, -ar
⁃ animal, animālis (n)
⁃ exemplar, exemplāris (n)
⁃ mare, maris (n)
⁃ rēte, rētis (n)
D. nouns in -er whose with stems ending in 2 or more
⁃ imber, imbris (m)
⁃ linter, lintris (m/f)
Does this make sense? I must admit the list looks daunting in the number of exceptions, but compiling it has helped me understand it a bit better, I think. I’d be very grateful if those who know could point out anything I’ve missed or misunderstood.
Hello. It’s a very good question and it’s not easy to solve it completely. But I can give you some help about the subject. Referring to substantives, in the third declension there are two groups: the type ending with consonant (genitive -um) and the type in -i- (genitive -ium). The type in consonant normally has different number of syllables in nominative and genitive: miles, militis, for example. In the type in -i- there are two main groups:
1.- With the same number of syllables in nominative and genitive; both cases usually end in -is: hostis, hostis; navis, navis.
2.- With different number of syllables in nominative and genitive, but with two consonants before the genitive desinence: ars, artis; mons, montis.
Both of these two groups show the plural genitive in -ium. I don’t know the reason why animal, animalis has the plural genitive animalium. According to my explanation this example would be included in the type in consonant. If you find the reason, tell me. I would be thankful. In any case it is a very concrete example. My general explanation is quite clear and works almost in all the cases.
Hi!
I think I know the answer to your question. According to the textbook* I’m studying from, there are the “Originally Parisyllabic” nouns in that 3rd declension which are nouns that have more syllables in the Gen. Sing. than in Nom. Sing. but are not considered Imparisyllabic because they originally had the same number of syllables in Nom. Sing. and in Gen. Sing.
e.g: Pars - Partis (f) Nom. Sing. “Pars” originally was “Parse” but the vowel “e” was omitted for phonetic conveniences.
And the Gen. Pl. of those nouns ends in (-ium)
Now, coming to the “Originally Parisyllabic” Neuter nouns. They end in (-al) or (-ar) which are shortened from (-ale) or (-are)
e.g: Animal - Animalis , it is declined like Mare-Maris
And the Gen. Pl. of those nouns ends in (-ium)
I hope this helps!
*Ashraf Farrag’s, a professor of the comparative linguistic sciences.