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Latin Nouns of the Third Declension - Endings

The Cases and Endings of 3rd Declension Latin Nouns

By N.S. Gill, About.com Guide

Latin Declension Rules | Latin Declensions > Third Declension

"The Third Declension is in a sense a catch-all for various stem-types, and can be very confusing" according to William Harris.

The nominative singular of a third declension noun may end in:

a (of Greek origin [for more on declining Greek nouns in Latin, see Latin Third Declension Nouns of Greek Origin]), e, o, c (rare), d, l, n, r, s, t (caput and compounds), or x,

according to James Ross' 18th century Latin grammar, who also describes the endings used by different genders:

Nouns can be masculine (especially with endings in -er, -or, -os, -n, or -o );
feminine (especially -do and -go endings); or
neuter (especially nouns ending in -c, -a, -l, -e, -t, -ar, -men, -ur, or -us) in gender.

2 Basic 3rd Declension Types

Third Declension nouns may have a consonantal or i-stem.

Consonantal

Note: For the consonantal stems, it may take some practice to figure out where to add the endings, although, the dictionary form should make this clear.

The usual genitive ending of third declension nouns is -is. The letter or syllable before it usually remains throughout the cases.

For the masculine and feminine, the nominative replaces the -is ending of the singular with an -es for the plural. (Remember: neuter plural nominatives and accusatives end in -a.) Similarly, the dative plural is formed from the singular with the addition of -bus. Sometimes the root vowel appears to change, as in our second paradigm word below, opus, operis, n.

First, here are the consonantal-stem's endings:

SINGULAR (the second form is for the neuter)
NOM. -/-
GEN. -is/-is
DAT. -i/-i
ACC. -em/-
ABL. -e/-e

PLURAL
NOM. -es/-a
GEN. -um/-um
DAT. -ibus/-ibus
ACC. -es/-a
ABL. -ibus/-ibus

Using rex, regis, m. (king), here is the paradigm:

SINGULAR

NOM. rex
GEN. regis
DAT. regi
ACC. regem
ABL. rege

LOC. regi or rege
VOC. rex

PLURAL

NOM. reges
GEN. regum
DAT. regibus
ACC. reges
ABL. regibus

LOC. regibus
VOC. reges

Using opus, operis n. (work), here is the paradigm:

SINGULAR

NOM. opus
GEN. operis
DAT. operi
ACC. opus
ABL. opere

LOC. operi or opere
VOC. opus

PLURAL

NOM. opera
GEN. operum
DAT. operibus
ACC. opera
ABL. operibus

LOC. operibus
VOC. opera

I-Stems

Some nouns of the third declension are called i-stem nouns; still others are mixed i-stem. I-stem nouns have a genitive plural ending in -"ium." Their ablative may not end in "-e," but may instead end in "-i." Other cases may also replace the "-e-" with an "-i-," so you might see an accusative singular ending in "-im." A neuter i-stem noun, animal, animalis (animal), looks a little different from other neuter 3rd declension nouns in the plural because of the "i" which makes the nominative and accusative plural of animal: animalia. The word for sea, mare, maris, is another neuter i-stem noun. Hostis, hostis is a generally masculine i-stem noun, but hostis can be feminine. The fact that the nominative and genitive is the same for this masculine or feminine noun indicates that it's an i-stem.

You would decline the name of Caesar thus:
Caesar, Caesaris, Caesari, Caesarem, Caesare.

For another i-stem, auris, see Auris, Aurum, and Aura.

Please note: Latin Declensions