The Latin Third Declension: rex, corpus, urbs, mare

The third declension is the biggest family of Latin nouns and holds many of the commonest, among them rex, corpus and urbs. Its genitive singular ends in -is, and that genitive hands you the stem the nominative hides. Here are its three patterns side by side.

Read across: the endings barely change. The neuter has no separate accusative and a plural in -a; the i-stem differs in one slot, -ium. Everything hard about this declension is in the first row.

The genitive is not optional here

In the first two declensions the nominative usually shows you the stem. Here it often does not, so the genitive is the only way into the noun:

Every other case is built on that stem, never on the nominative:

• Regem video. - I see the king.
• Hominem video. - I see the person.
• Militem video. - I see the soldier.

Paradigm one: consonant stems

This is the default pattern. Rex, regis, king, masculine:

Seven endings to learn, and -es and -ibus each fill two slots. A feminine noun takes exactly the same endings: lex, legis, law, gives legem, lege, legum.

• Nomen regis scio. - I know the king's name.
• Legem non habemus. - We do not have a law.
• Milites veniunt. - The soldiers are coming.

Paradigm two: neuters

Every neuter noun in Latin, in every declension, has one form for subject and object, and in the plural that form ends in -a. Corpus, corporis, body:

Tempus, genus, opus and caput all run this way:

• Corpora in terra sunt. - The bodies are on the ground.
• Nomina eorum scio. - I know their names.
• Tempus fugit. - Time flies.

The cost: on a neuter the ending cannot tell subject from object, so the verb and the other nouns settle it.

Paradigm three: i-stems

Some third-declension nouns kept an old -i-. For masculines and feminines it shows in one slot you will notice: the genitive plural is -ium, not -um. Urbs, urbis, city, feminine:

• Rex urbium - the king of the cities
• Magna pars navium - a large part of the ships

Older texts and poets also write an accusative plural in -is (urbis for urbes): recognise it, do not produce it.

Neuter i-stems, the ones in -e, -al and -ar, go further: ablative singular -i and plural -ia. Mare, maris, sea:

• In mari naves sunt. - There are ships in the sea.

Spotting an i-stem

The exceptions catch everyone. These look like i-stems (pater, mater and frater have as many syllables as their genitives and a stem ending in two consonants; iuvenis and canis fit rule one exactly) and are not:

And vis, force, is irregular in its own right: plural vires, genitive virium.

Gender: learn it with the word

In the first declension almost everything is feminine; in the third the nominative is a poor guide. Adjectives must agree, so a wrong guess makes wrong Latin.

• Rex bonus est. - The king is good.
• Urbs magna est. - The city is large.
• Corpus magnum est. - The body is large.

The patterns that genuinely hold:

Two carve-outs. Uxor and arbor are feminine despite -or (and a few -or nouns, such as aequor, sea, are neuter): uxor bona, a good wife. And the -us nouns split by genitive: corpus, corporis is neuter, virtus, virtutis feminine.

123

1. 1caput
2. 2os
3. 3pes

Caput (the head) and os (the mouth) are neuter, pes (the foot) is masculine. All three are third declension, and their nominatives do not say so.

Learn the dictionary entry whole: rex, regis, masculine, is one fact, not three.

Mistakes English speakers make

What to do next

1. Learn every new noun with its genitive and gender: nox, noctis, feminine.
2. Do the drill below: build forms on the stem, then sort by -um and -ium.
3. Then Latin word order, which these endings make free.