In Latin, nouns are declined according to how they are used in a sentence. That is, by their case. There are five major cases in Latin, each corresponding to one of the major uses of nouns.

The cases, and an explaination of their function are as follows:

  1. Nominative - The nominative case is used for the subject of a sentence, as well as for preidcate nominatives.
  2. Genitive - The genitive case is used to express posession, as well as use in the partitive.
  3. Dative - The dative case is used for indirect objects, certain special adjectives, as well as a special use called the dative of reference.
  4. Accusative - The accusative case is used with the direct object, certain prepositions and for the expression of certain time-space relationships.
  5. Ablative - The ablative case is used with the remainder of prepositions, the ablative of means and the ablative of time.

In addition to these five, there is the vocative case, which is used for commands.

In order to express case, nouns in Latin change their endings to express the change. There are five different declensions, or groups by which these changes occur. Those endings are as follows:

Case, I, II, III, IV, V
Singular
Nominative, a, us/er/um, *, us/û, ês
Genitive, ae, î, is, ûs, ei
Dative, ae, ô, î, uî/û, eî
Accusative, am, um/us, em/*, um/û, em
Ablative, â, ô, e/î, û, ê
Plural
Nominative, ae, î/a, ês/a/îa, ûs/ua, ês
Genitive, ârum, ôrum, um/ium, uum, êrum
Dative, îs/âbus, îs, ibus, ibus, êbus
Accusative, âs, ôs/a, ês/a/ia, ûs/ua, ês
Ablative, îs/âbus, îs, ibus, ibus, êbus