The 6 Cases of Latin Nouns

There are six cases of Latin nouns that are commonly used. Another two—locative and instrumental—are vestigial and are not often used. 

Nouns, pronouns, adjectives, and participles are declined in two numbers (singular and plural) and in six principal cases.

The Cases and Their Grammatical Position in Sentences

1. Nominative (nominativus): Subject of the sentence.
2. Genitive (genitivus): Generally translated by the English possessive, or by the objective with the preposition of.
3. Dative (dativus): Indirect object. Usually translated by the objective with the preposition to or for.
4. Accusative (accusativus): Direct object of the verb and object with many prepositions. 
5. Ablative (ablativus): Used to show means, manner, place, and other circumstances. Usually translated by the objective with the prepositions "from, by, with, in, at."
6. Vocative (vocativus): Used for direct address.

Vestigial Cases: Locative (locativus): Denotes "the place where." This vestigial case is often left out of Latin noun declensions. Traces of it appear in names of towns and a few other words: Rōmae ("at Rome") / rūrī ("in the country"). Still another vestigial case, the instrumental, appears in a few adverbs.​ All the cases, except the nominative and vocative, are used as object cases; they are sometimes called "oblique cases" (cāsūs oblīquī).

Five Declensions of Nouns and Their Endings

Nouns are declined according to gender, number, and case (a declension is essentially a fixed pattern of endings). There are only five regular declensions of nouns in Latin; there is a sixth for some pronouns and adjectives that end in -ius in the genitive case form. Each noun is declined according to number, gender, and case. This means that there are six sets of case endings for five declensions of nouns—one set for each declension. And students have to memorize them all. Below are brief descriptions of the five noun declensions, with links to the full declension for each, including the case endings for each declension.

1. First declension nouns: End in -a in the nominative singular and are feminine.

2. Second declension nouns:

• Most are masculine and end in -us, -er or -ir.
• Some are neuter and end in -um.

Esse: The all-important irregular verb esse ("to be") belongs to this group. Words associated with it are in the nominative case. It does not take an object and should never be in the accusative case.

The following is a sample paradigm* of the second declension masculine noun somnus, -i ("to sleep"). The case name is followed by the singular, then the plural.

*Note that the term "paradigm" is frequently used in discussions of Latin grammar; a "paradigm" is an example of a conjugation or declension showing a word in all its inflectional forms.

• Nominative somnus somni
• Genitive somni somnorum
• Dative somno somnis
• Accusative somnum somnos
• Ablative somno somnis
• Locative somni somnis
• Vocative somne somni

3. Third declension nouns: End in -is in the genitive singular. That's how you identify them.

4.​ Fourth declension nouns: Ending in -us are masculine, apart from manus and domus, which are feminine. Fourth declension nouns ending in -u are neuter.

5. Fifth declension nouns: End in -es and are feminine.
The exception is dies, which is usually masculine when singular and always masculine when plural.