3 declension nouns and adjectives

3 rd declension nouns and adjectives
Reading the Reading Latin vocabulary entry:
rex reg-is 3m
Nom. sing.
"dictionary form"
The stem (reg-) plus the
gen. sing. ending (is)
Tricky things about 3 rd declension nouns.
The declension number
(which you can deduce
from the gen. endings)
and the gender.
• They can be masculine, feminine, or neuter. The other declensions are
overwhelmingly feminine (1 st and 5 th ) or overwhelmingly masculine or neuter (2 nd and
4 th ). In reading Latin, the gender of the noun matters mainly when one is trying to
figure out which noun an adjective modifies. Reading Latin gives some hints on
predicting the gender of 3 rd declension nouns on page 496.
• The stem cannot easily be predicted from the nom. sing. Hence you may have
trouble looking up 3 rd declension nouns when you see inflected forms. And given the
variety of nom. sing. forms, you may not even know you've got a noun, much less a 3 rd
declension noun. Reading Latin gives some hints on predicting nominatives from
genitives on page 496.
Regular (= non i-stem) nouns
Masculine and feminine nouns use the same endings.
Singular Eg., fûr, fûr-is 3m. Plural
N --- fûr -ês fûrês
Acc -em fûrem -ês fûrês
G -is fûris -ium fûrum
D -î fûrî -ibus fûribus
Abl -e fûre -ibus fûribus
No form is listed for the nom. sing. as there are many different types.
Note that in the plural the nom = acc and the dat = abl. Come to think of it,
the dat. pl. = abl. pl. in all declensions.
Do not mistake the gen. pl. for a 2 nd declension neuter (like somnium).

Neuters use the same endings, but, like all other neuter nouns, follow two rules.
• All neuter nouns have the same forms in the nom. & acc.
• All neuter plurals end in –a in the nom. & acc. plural. Don't confuse them with
first declension nouns.
Hence the neuter noun onus, oner-is has onus also in acc. sing. (not *onerem), and
nom. & acc. pl. are onera (not *oneres).
i-stem nouns
Reading Latin does a poor job with these. There are rules to determine which nouns
are i-stems.
• All neuters with nom. sing. in –al, -ar, or –e are i-stems. Eg. animal, animal-is.
Gen. pl. = animalium. And they end in –ia in the nom. pl.
• Masculine & feminine nouns ending in –is or –ês in the nom. sing, when the
gen. singular has the same number of syllables. Eg.: civis, civ-is. Gen. pl. =
civium.
• Masculine & feminine nouns with nominatives in –s or –x, when the stem
ends in two consonants. Eg.: mons, mont-is (mountain). Gen. pl. = montium.
But the stem of rex, reg-is doesn't end in two consonants, so gen. pl. = regum.
Most important is to know is that i-stem nouns differ
• in the genitive plural, where they always have –ium (instead of –um)
• in the accusative plural, where they often have –îs (instead of –ês).
Contrast this form with the short –is of the gen. sing. Later on (say, after the
time of Augustus) even i-stems tend to go with –ês, by the way.
• in the ablative singular, where they may have –î (instead of –e). This is
most common with neuters.
Compare below fur and aes, with the differing forms of aes in bold.
fûr, fûr-is aes, aed-is
N fûr aes fûrês aedês
Acc fûrem aedem fûrês aedîs
Gen fûris aedis fûrum aedium
D fûrî aedî fûribus aedibus
Abl fûre aede (or aedî ) fûribus aedibus

3 rd declension adjectives
3 rd declension adjectives can modify nouns of any declension, just as 1/2 declension
adjectives (like magn-us, a um) can. Like all adjectives, they must agree with the noun
they modify in case, number, and gender (though this doesn't mean they have to be
spelled the same way). And, like all adjectives, they are sometimes used without
nouns, as substantives. In this case, masculine forms refer to men (or people in
general), feminine forms to women, neuter forms to things. Cf. GVE 14.
All 3 rd declension adjectives are i-stems. And they use all three i-stem features noted
above (though –ês tends to replace –îs after Augustus).
3 rd declensions adjectives are a bit confusing in the nominative singular. They come in
three types.
• Most 3 rd declension adjectives have two different forms in the nominative
singular, -is for masc. and fem., -e for neuter. Eg., omn-is, omne. These are
called "two termination adjectives."
• Some 3 rd declension adjectives have only one form in nom. sing. Eg., ingens,
ingent-is. Here ingentis is the genitive singular, listed so that one may identify
the stem. These are "one termination adjectives."
• A few 3 rd declension adjectives have three forms. All end in –er in the
masculine sing. Egs. celer, celer-is, celere; acer, acr-is, acre. "Three termination
adjectives."
Reading Latin cleverly inserts a hyphen on the form from which we get the stem. This
form varies from adjective to adjective. With adjectives of two or three terminations
we use the feminine nom. sing. (as we do with 1/2 adjectives like noster, nostr-a,
nostrum). With adjectives of but one termination we need to list the gen. sing.
Neuters. Keep in mind that these follow the rules for other neuters, so that the acc.
sing. will always be the same as the nom. sing dictionary form, and neut. pl. will always
end in –ia.
Some good news
For beginners, it's a bummer that adjectives don't always end with the same letters
that their nouns do (though they must agree in case, number, and gender). But
sometimes this helps. Eg.: what case is turbae (mob)? Well, ingentes turbae must be
nom. pl., ingenti turbae must be dat. sing., and ingentis turbae must be gen. sing. Ah,
what a relief!