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Nouns in -ius, -er and -ir

fīlius, puer, ager, vir: second-declension nouns with a twist.

LatinBeginning Latin · The second declensionAbout 4 min: 1 reading, 3 practiceUpdated

After this lesson you can
  • Form the genitive of nouns in -ius and -ium, and the vocative of nouns in -ius
  • Decline puer, ager and vir
  • Tell from the genitive whether the e stays or drops
Latin Level 1: nouns and cases: lesson 9 of 13
  1. Beginning Latin · Sounds
  2. Saying Latin out loud 4 min
  3. Beginning Latin · How sentences work
  4. Endings do the work 3 min
  5. The five cases 3 min
  6. Beginning Latin · Nouns
  7. The first declension 3 min
  8. Adjectives agree with their nouns 3 min
  9. Beginning Latin · The second declension
  10. The second declension 4 min
  11. Predicate nouns and apposition 3 min
  12. Adjectives in all three genders 3 min
  13. Nouns in -ius, -er and -ir 4 min
  14. Beginning Latin · Pronouns and adjectives
  15. My, your, his, our 3 min
  16. Beginning Latin · The ablative
  17. Four ways to say "with" 3 min
  18. Beginning Latin · Pronouns and adjectives
  19. The nine irregular adjectives 4 min
  20. is, ea, id: this, that, he, she, it 3 min

Try first

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Pairs with D'Ooge, Latin for Beginners (Ginn, 1909), Lessons XII–XIII, §§ 87–94

What it is

Two small groups of second-declension nouns need care.

Nouns in -ius and -ium have a genitive singular in a single -ī: fīlius (son) → fīlī; praesidium (garrison) → praesidī. Names in -ius, and fīlius, also have a vocative in -ī: Vergilī! (O Vergil!), fīlī! (O son!). The rest is regular.

Nouns in -er and -ir have no ending in the nominative singular:

puer, boyager, fieldvir, man
Nom.pueragervir
Gen.puerīagrīvirī
Acc.puerumagrumvirum
Nom. pl.puerīagrīvirī

The genitive shows whether the e stays (puer, puerī) or drops (ager, agrī).

Quick check

Tap an answer to check it.

  1. What is the genitive singular of ager?

    Show answer

    agrī. ager, agrī: the e is only in the nominative.

Why it matters

These are everyday words: fīlius, puer, vir, ager, magister (teacher). As a plural noun, līberī means children (literally "the free-born"). Adjectives follow the same split: līber, lībera, līberum (free) keeps its e, like puer; pulcher, pulchra, pulchrum (beautiful) drops it, like ager.

Worked example

  • Fīlī, ubi est equus? → Son, where is the horse? (vocative fīlī)
  • Virī agrōs arant. → The men plough the fields.
  • Magister puerōs laudat. → The teacher praises the boys. (magister, magistrī, like ager)

Common mistake

Guessing whether the e stays. Puer keeps it (puerī), but ager drops it, so wrong: agerī is wrong: agrī. Always learn the genitive with the noun.

Key terms

fīlius, fīlī, m.
son
puer, puerī, m.
boy
ager, agrī, m.
field
vir, virī, m.
man
līberī, -ōrum, m. pl.
children (literally "the free-born")

Practise the key terms

Tap a card to turn it over. 5 cards.

FrontBack
fīlius, fīlī, m.son
puer, puerī, m.boy
ager, agrī, m.field
vir, virī, m.man
līberī, -ōrum, m. pl.children (literally "the free-born")

Practice

Quick quiz

Tap an answer to check it.

  1. How do you call out "O son!"?

    Show answer

    fīlī. fīlius and names in -ius have a vocative in -ī.

  2. What is the accusative plural of vir?

    Show answer

    virōs. vir, virī, m.: accusative plural virōs.

  3. Which adjective form goes with puella (feminine): "a beautiful girl"?

    Show answer

    puella pulchra. pulcher, pulchra, pulchrum.

Recognition drill

Pick the right answer, as fast as you can.

All pairs

Tap a card to turn it over. 6 cards.

FrontBack
fīliusfīlī
praesidiumpraesidī
puerpuerī
ageragrī
virvirī
magistermagistrī

Practise speaking

Studyfern has no voice tools of its own. To practise out loud, copy this prompt into a voice-capable AI assistant and talk with it.

You are a patient Latin tutor. Use the classical pronunciation only, never the Church one: c is always k, g is always hard, v sounds like w, ae like the ai in aisle, and long vowels are held longer. Speak slowly. Use only these Latin words: fīlius, puer, ager, vir, līberī, magnus. Ask me for forms of these nouns, for example the genitive singular of fīlius or the accusative plural of ager, and I will say them aloud. Do 10 forms. After each answer, tell me what kind of mistake I made, if any, and let me try again, then tell me one thing to improve. Keep every reply under 2 sentences. If I need a name or a town, I will make one up. Speak English except for the Latin itself.

Listen too. Listen to native speakers before and after: see the free listening and shadowing links.

Good to know. AI feedback on pronunciation is hit and miss, so check yourself against native recordings. This course teaches the classical pronunciation (see lesson 1); AI voices may mix it with the Church (Italian-style) one, so ask for classical and check against lesson 1. Don't share personal details: use a made-up name and town.

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In short

  • -ius / -ium nouns: genitive singular in -ī (fīlī, praesidī).
  • fīlius and names in -ius: vocative in -ī (fīlī, Vergilī).
  • puer keeps its e (puerī); ager drops it (agrī); vir is regular (virī).
  • Learn the genitive with every noun.

Mastery check

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Check yourself

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  1. Give the genitive plural of puer.

    Show answer

    puerōrum.

  2. What does līberī mean?

    Show answer

    Children.

  3. Is magister like puer or like ager?

    Show answer

    Like ager: magister, magistrī.

Further reading

  • D'Ooge, Latin for Beginners, Lessons XII–XIII, §§ 87–94. Public domain; Project Gutenberg.