Fourth Declension: -us, -ius

The Fourth Declension

Level 3

Masculine nouns in -us and -ius follow the fourth declension: sūnus, sūnaus, sūnui, sūnų (son). The same pattern gives iš Vilniaus (from Vilnius) and Vilniuje (in Vilnius).

How It Works

Singular

  • Nominative: sūnus · Vilnius
  • Genitive: sūnaus · Vilniaus
  • Dative: sūnui · Vilniui
  • Accusative: sūnų · Vilnių
  • Instrumental: sūnumi · Vilniumi
  • Locative: sūnuje · Vilniuje
  • Vocative: sūnau! · Vilniau!

Plural

Nouns in -us keep a u: sūnūs, sūnų, sūnums, sūnus, sūnumis, sūnuose. Watch the long ū: sūnūs is the subject form and sūnus the object form. Nouns in -ius take first-declension plural endings: skaičiai, skaičių, skaičiams, skaičius, skaičiais, skaičiuose. See The First Declension and Plural Case Endings.

Which words?

  • -us: sūnus (son), turgus (market), medus (honey), alus (beer), lietus (rain), dangus (sky), cukrus (sugar)
  • -ius: skaičius (number), vaisius (fruit), amžius (age), profesorius (professor)
  • places and names: Vilnius, Paryžius, Paulius, Andrius

Žmogus (person) follows this pattern in the singular (žmogaus, žmogui), but its plural is a different word: žmonės, žmonių.

Names in -ius take the vocative -iau when you speak to someone: Labas, Pauliau! See Vocative Address. For iš Vilniaus and Vilniuje, see From With Iš and Locative of Place.

Examples (6)

  1. Mano sūnus gyvena Vilniuje.

    My son lives in Vilnius.

    Word by Word: My son lives in-Vilnius.

    Vilnius takes the locative -uje: Vilniuje.

  2. Šeštadienį einame į turgų.

    On Saturday we are going to the market.

    Word by Word: On-Saturday (we) go to market.

    turgus becomes turgų, the accusative, after į.

  3. Esu iš Vilniaus.

    I am from Vilnius.

    Word by Word: (I) am from Vilnius.

    After iš, Vilnius takes the genitive -aus.

  4. Kiek kainuoja kilogramas medaus?

    How much does a kilogram of honey cost?

    Word by Word: How-much costs kilogram of-honey?

    medus becomes medaus, the genitive after an amount.

  5. Jie turi du sūnus.

    They have two sons.

    Word by Word: They have two sons.

    The object form is sūnus with a short u; the subject form is sūnūs.

  6. Labas, Pauliau! Kaip sekasi?

    Hi, Paulius! How are you?

    Word by Word: Hi, Paulius! How goes?

    Names in -ius take the vocative -iau.

Common Mistakes

  • Using the nominative after iš.

    Esu iš Vilnius.
    Esu iš Vilniaus.

    Iš takes the genitive, and fourth-declension nouns form it with -aus.

  • Using the subject form sūnūs as an object.

    Jie turi du sūnūs.
    Jie turi du sūnus.

    Sūnūs (long ū) is the subject; after turi the object form is sūnus (short u).

  • Giving an -ius noun the plural of sūnus.

    Šie skaičiūs teisingi.
    Šie skaičiai teisingi.

    Nouns in -ius form the plural like the first declension: skaičiai, skaičių.

How It Connects

Tap a pattern to see what it builds on and what it leads to.

Fourth Declension: -us, -iusLevel 3The Fourth Declension

Learn This First

The fourth declension organizes -us nouns and the mixed plural behavior of -ius nouns.

Words in This Pattern

sūnusturgusskaičiusVilnius