TEM: Lesson - Introduction to Third Declension i-Stem Nouns

Introduction to 3rd Declension i-stem Nouns

Most of the nouns in this module's vocabulary list are a special subset of 3rd Declension nouns called 3rd Declension i-stem. These nouns add an extra -i into some inflections (endings). It's important to watch out for i-stem nouns when working with 3rd Declension nouns.

How to Identify a 3rd Declension i-stem Noun

There are 3 basic rules which will help you to determine if a noun is an I-stem.

3rd Declension i-stem Rules
Rule Examples

Masculine and Feminine 3rd Declension Nouns which:

  • have a nominative singular ending in -is or -es.
  • have the same number of syllables in both the nominative and genitive singular
  • civis, civis, m./f.
  • valles, vallis, f.

Note how both nominative and genitive have the same number of syllables.

Masculine and Feminine 3rd Declension Nouns which:

  • have one syllable in the nominative singular that ends in -s or -x.
  • have a base than ends in two consonants.
  • mons, montis, m.
    • Base: mont-
  • nox, noctis, f.
    • Base: noct-

Neuter 3rd Declension Nouns which:

  • have a nominative singular ending in -al, -e, or -ar.
  • animal, animalis, n.
  • mare, maris, n.