3rd Declension i-stems and 4th and 5th Declensions

Table of contents

1. 3rd Declension i-stem Nouns
   1. Masculine and Feminine i-stems
   2. Neuter i-stems
2. 4th and 5th Declension
   1. 4th Declension
      1. 4th Declension Masculine/Feminine
      2. 4th Declension Neuter
      3. domus and the Locative Case
   2. 5th Declension

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3rd Declension i-stem Nouns

Because the cognitive load of adding the perfect passive and the imperfect tense into our verbal knowledge base is a lot, we’ll take a brief detour to fill out the full picture of nouns by introducing a special sub-group of 3rd declension nouns and then the 4th and 5th declensions.

As a reminder, 3rd declension nouns are those that have an -is in the genitive singular form of the dictionary entry. These nouns are generally grouped into masculine and feminine 3rd declension nouns and neuter 3rd declension nouns, because of the differences in some of the endings across similar case-number combinations. For example, note the ending differences between nouns like dux, ducis, m. - leader and nōmen, nōminis, n. - name:

There is a special sub-group of third declension nouns known as i-stems. These nouns include an -i- in certain case/number endings:

• masculine, feminine, and neuter i-stems have the ending -ium in the genitive plural, rather than the expected -um.
• neuter i-stems alone also use -ī as the ablative singular ending (rather than the expected -e) and -ia as the nominative and accusative plural ending (rather than the expected -a).

These i-stem noun endings generally match up to the i-stem endings that we learned about in 3rd declension adjectives. However, while those endings are applied to all 3rd declension adjectives, there are only certain 3rd declension nouns that will follow those patterns.

We can identify an i-stem based on the nominative and genitive forms in the noun’s dictionary entry according to the following rules:

Masculine and Feminine i-stems

1. parisyllabic: the nominative ends in -is or -ēs, and the nominative and the genitive have the same number of syllables (pari- from Latin par, “equal”). Some examples of parisyllabic i-stems include:

• hostis, hostis, m. - enemy (gen. pl. = hostium)
• nāvis, nāvis, f. - ship (gen. pl. = nāvium)
• cīvis, cīvis, m./f. - citizen (gen. pl. = cīvium)

2. monosyllabic and double consonant: the nominative ends in -s or -x, and the noun stem ends in two consonants. Often, the nominative is a single syllable (mono- from Greek monos, “one, only, lone”). Some examples include:

• ars, artis, f. - art, skill (gen. pl. = artium)
• nox, noctis, f. - night (gen. pl. = noctium)
• urbs, urbis, f. - city (gen. pl. = urbium)

Note that the only difference in declension between these masculine and feminine i-stems versus regular masculine and feminine third declension nouns is the extra -i- in the genitive plural ending. Otherwise, declension is completely regular. For example, for urbs, urbis, f. - city:

Thus:

• cīvēs illārum urbium laetī erant.
  • The citizens of those cities were happy.

BUT this -ium ending applies only to masculine and feminine 3rd declension i-stem nouns. Otherwise, 3rd declension nouns will use the regular -um ending in the genitive plural:

• fīliī sapientium patrum in viam currēbant.
  • The sons of the wise fathers were running into the road.

Here, the 3rd declension noun patrum has its regular -um genitive plural ending; the adjective paired with it, sapientium, however, uses the i-stem ending because it’s a 3rd declension adjective.

Neuter i-stems

3. -al, -ar, -e: the nominative ends in -al, -ar, or -e. Examples include:

• animal, animālis, n. - animal (abl. sg. = animālī; nom. and acc. pl. = animālia; gen. pl. = animālium)
• mare, maris, n. - sea (abl. sg. = marī; nom. and acc. pl. = maria; gen. pl. = marium)

Note that only neuter i-stems use an i in the abl. sg. and nom. and acc. pl. forms (in addition, they use it in the gen. pl., a trait shared with masculine and feminine i-stems). Masculine and feminine i-stems use the i only in the gen. pl.

Here is a sample paradigm chart for mare, maris, n. - sea:

The ablative singular ending (-ī) of a neuter i-stem noun in particular poses problems due to its similarity to the dative singular. This is where you can use the context of words around the noun to figure out which case is more appropriate. For example, compare the following two sentences:

• puer cībum animālī dābat.
• nāvis in marī erat.

In the first sentence, the main verb dābat, from dāre, “to give”, often expects an indirect object, so if we try taking animālī as dative, it makes for a sound translation: “The boy was giving food to the animal.” In the second sentence, on the other hand, the word marī is preceded by the preposition in, which can take objects only in the accusative or ablative case. Thus, we can consider it an ablative of place where: “The ship was on the sea.”

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4th and 5th Declension

Beyond the first three declensions, into which all of our nouns have been classified so far, there also exist a 4th and 5th declension. We can determine nouns that belong to those declensions in the same way that we classified nouns that belong to the first three: based on the genitive singular ending in the noun’s dictionary entry.

For the 4th declension, note specifically the long mark on the -ūs genitive singular ending, which will be important for disambiguating it from other cases and numbers.

The 5th declension genitive singular ending of -eī / -ēī can also be confused with the 2nd declension genitive singular ending of -ī. When you see an -ī at the end of the genitive singular form in a dictionary entry, you have to then look at the nominative singular form to further disambiguate: 2nd declension nouns will have a nominative singular that ends in -us, -r, or -um, while 5th declension nouns will have a nominative singular that ends in -ēs. More on this below.

4th Declension

4th declension nouns, like 3rd and 2nd, can be subdivided into a masculine/feminine group and a neuter group, since their endings will differ. These nouns include ones like the following:

• manus, manūs, f. - hand; armed force (of soldiers)
• lacus, lacūs, m. - lake
• genū, genūs, n. - knee

Again, while gender, case, and number mean the same things across all 5 declensions, the endings that can indicate case-number combinations will necessarily be different across each declension. Thus, the endings that we can use for 4th declension nouns break down into two paradigm charts, one for masculine/feminine 4th declension nouns and one for neuter 4th declension nouns:

4th Declension Masculine/Feminine

Note the preponderance of the letter u in most of these endings. In particular, look out for the long mark over the u in the genitive singular, nominative plural, and accusative plural, as that long mark is the only way to differentiate those case-number combinations from the short -us of the nominative singular. Thus:

• lacus multa animālia habuit. (nominative singular)
  • The lake had many animals.

But:

• mīles manūs hostium vīdit. (accusative plural)
  • The soldier saw the armed forces of the enemies.

4th Declension Neuter

The 4th declension neuter chart is, frankly, annoying due to the ending -ū appearing in four of the singular categories. Thus, it will become very important to use context clues to disambiguate. For example:

• liber in genū patris positus est.
  • The book was placed on the knee of the father.

The preposition in that precedes genū can take only the accusative or ablative case as an object; thus, ablative of place where makes sense here. (Accusative is technically possible here, for accusative of motion toward, but it would result in a translation that doesn’t necessarily make sense: “The book was placed into the knee of the father”).

• genū animālis magnum erat.
  • The knee of the animal was large.

The linking verb erat does not expect an accusative direct object but rather functions mostly with nominative case substantives to serve as a subject and a predicate nominative.

domus and the Locative Case

One special 4th declension noun is domus, domūs, f. - house, home, because while it exhibits many 4th declension noun endings, in some cases and numbers it can use 2nd declension noun endings either as an alternative to the 4th declension ending or as the primary ending. Here is the paradigm chart:

Thus:

• virī ē domibus illīs cucurrērunt. The men ran out of those homes. (-ibus as 4th declension ending)

but:

• vir domōs illōrum vīdit. The man saw the homes of those people. (-ōs as a 2nd declension ending)

In addition, there exists a special case and use that applies to very few nouns, including domus, called the locative case, which indicates the place where or in which an action occurs. While most nouns use the ablative case and a preposition to indicate place where or in which, domus will have a special case ending and use without a preposition to mean “at home”: domī. Thus:

• fīliae domī ultimam noctem dormiēbant.
  • The daughters were sleeping at home for the final night.

The locative only appears in domus; rus, ruris, n. - countryside (locative: rure); humus, humī, m. - ground (locative: humī); and certain city and town names (like Rōma, Rōmae, f. - Rome – locative: Rōmae). Thus:

• puerī humī sēdērunt.
  • The boys sat on the ground.
• dux mīlitēs Rōmae vīdit.
  • The leader saw the soldiers at Rome.

5th Declension

5th declension nouns are masculine or feminine (no neuter) and exhibit endings that can be summarized in one chart. You’ll notice alternatives with long marks in some endings, but these long marks are negligible.

Two of the most common 5th declension nouns are the following:

• diēs, diēī, m. - day
• rēs, reī, f. - thing, matter, situation, affair

And again, cases and uses work the same way, just with different endings for 5th declension nouns:

• prīmō diē agricola equōs duxit.
  • The farmer led the horses on the first day.
• ille ā malā rē currēbat.
  • That man was running away from a bad situation.

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