Case Name
and Typical Meaning / Use

Sing./Plural
Endings

Examples

Nominative

The "subject case": the subject is the word found by asking WHO or WHAT before the verb.

-US /
-ER

-Î

puer, puerî

Puer amicus est.
  The boy is a friend.
Puerî amicî sunt.
  The boys are friends.

Genitive

The "possession case": The genitive word corresponds to the word that takes an apostrophe in English. If (A) is in the genitive, (A) possesses something else (B), with the emphasis falling on (B), so that (A) is somewhat like a modifier of (B): in student's book (= discipuli liber), the possession-word qualifies the meaning of the noun book. 

-Î

-ÔRUM

puerî, puerôrum

Amicus  puerî clamat.
  The boy's friend is shouting.
Numerus puerôrum magnus est.
 The number of boys is large.

Dative

The "indirect object case": the indirect object is found by asking TO / FOR WHOM? or TO / FOR WHAT? after the verb. Certain verbs govern the dative.

-Ô

-ÎS

puerô, puerîs

Puerô pecuniam dat.
  He is giving money to the boy.
Puerîs dona dat magistra.
  The teacher gives gifts to the boys (or children).

Accusative

The "direct object case": the direct object is usually found by asking WHO or WHAT after an action-verb whose action has a receiver. "We hold these truths." The accusative is also used after certain prepositions.

-UM

-ÔS

puerum, puerôs

Puella puerum videt.
  The girl sees the boy. 
Puerôs videt.
  She sees the boys.

Ablative

The "by-with-from case": Certain prepositions take objects in this case. Used alone it can have an adverbial meaning, e.g., indicating how something is done.

-Ô

-ÎS

puerô, puerîs

A puerô litterae scriptae sunt.
  The letter was written by the boy.
De puerîs multa scripsit magistra.
  The teacher has written many things about the boys (or children).