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.

-A

-AE

porta, portae

Porta magna est. The gate is large.
Patent portae.  The gates are open.

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. 

-AE

-ÂRUM

portae, portârum

magnitûdo portae  The size of the gate
portârum magnitudo  The size of the gates

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.

-AE

-ÎS

portae, portîs

Nullus est portîs custos.  There is no guard for the gates.

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.

-AM

-ÂS

portam, portâs

Ante portam oppidî.  Before the town's gate 
Portâs clausêrunt. They shut the gates.

Ablative

The "by-with-from case": Certain prepositions and certain verbs govern objects in this case. Used alone it can have an adverbial meaning, for example, to indicate by what means something is done.

-Â

-ÎS

portâ, portîs

In portâ consistit.  He made a stand in the gateway.
Prô portîs castrôrum  In front of the camp's gates.