TEM: Lesson - Declining 3rd Declension i-Stem Nouns

Declining 3rd Declension i-Stem Nouns

Now that you know how to identify a 3rd declension i-stem noun, it's time to learn what makes these nouns different from regular 3rd declension nouns. I-stem nouns change certain endings, adding an -i to the endings for some cases. Let's look closely at where those changes occur. Carefully compare the regular 3rd declension nouns below to the i-stem noun. Where are the changes?

Example Nouns Used Below:

  • 3rd Declension (regular):
    • miles, militis, m. - soldier. Base: milit-
  • 3rd Declension (i-stem):
    • mons, montis, m. - mountain. Base: mont-
Example Nouns - 3rd Declension Vs. i-stem - Masculine/Feminine
Case miles - Singular miles - Plural mons - Singular mons - Plural
Nominative miles milites mons montes***
Genitive militis militum montis montium
Dative militi militibus monti montibus
Accusative militem milites montem* montes***
Ablative milite militibus monte** montibus
Vocative miles milites mons montes***

Nota bene:

  • *On occasion, the accusative singular may end in -im
  • **On occasion, the ablative singular may end in -i
  • ***On occasion, the nominative, accusative and vocative plural ends in -is

Example Nouns Used Below:

  • 3rd Declension (regular):
    • iter, itineris, n. - journey. Base: itiner-
  • 3rd Declension (i-stem):
    • mare, maris, n. - sea. Base: mar-
Example Nouns - 3rd Declension Vs. i-stem - Neuter
Case iter - Singular iter - Plural mare - Singular mare - Plural
Nominative iter itinera mare maria
Genitive itineris itinerum maris marium
Dative itineri itineribus mari maribus
Accusative iter itinera mare maria
Ablative itinere itineribus mari maribus
Vocative iter itinera mare maria

Summary of Endings

The defining characteristic of an i-stem noun is that the genitive plural must be -ium. However, that's not all, as you can see by the words in bold above. The following changes are made to i-stem nouns in the 3rd declension:

  • All i-stem nouns
    • Genitive Plural:
      • [-ium] replaces [-um]
  • Neuter i-stem nouns
    • Ablative Singular:
      • [-i] replaces [-e]
    • Nominative, Accusative, Vocative Plural:
      • [-ia] replaces [-a]
  • Occasional/Possible Changes
    • Note: you do not need to memorize these, but you might see one of these changes at some point when working with Latin
    • Masculine/Feminine Accusative Singular:
      • Can be [-im] instead of [-em]
    • Masculine/Feminine Ablative Singular:
      • Can be [-i] instead of [-e] - only certain nouns will allow this, like ignis, ignis
    • Masculine/Feminine Nominative, Accusative, Vocative Plural:
      • Can be [-is] instead of [-es]

Practice Activity