The relation, in which a noun stands to some other word in the sentence or the change of form by which this relation is indicated, is called the Case.
There are five Cases in English.
(i) The Nominative Case
(ii) The Vocative Case
(iii) The Genitive Case (The Possessive Case)
(iv) The Accusative Case
(v) The Dative Case
When a Noun is used as the Subject to a Verb, it is in the Nominative Case.
When a Noun is used for the sake of address, it is in the Vocative Case.
When a Noun is used as the Direct Object of a Verb, it is in The Accusative Case.
When a Noun is used as the Object to a Preposition, it is also said to be in the Accusative Case.
When a Noun is used as the Indirect Object of a Verb, it is in The Dative Case.
The Genitive (or Possessive) Case usually denotes relationship or ownership.
Rain falls. (Nominative of Subject)
Birds fly. (Nominative of Subject)
Tiger roars. (Nominative of Subject)
Are you coming, father? (Vocative Case)
Sir, may I come in? (Vocative Case)
The man killed the rat. (Accusative Case)
They bought a house. (Accusative Case)
The earth is moistened by rain. (Accusative Case)
He gave the man a rupee. (Dative Case)
The Genitive (or Possessive) Case usually denotes relationship or ownership. It is formed by adding's (which is called apostrophe s) to the noun as following.
Plural — men's
Singular — man's
Omission of 's' :
There are three kinds of instances in which the apostrophe s is omitted.
(1) After all Plural Nouns ending in s such as…
The birds' nests
The dogs' kennels
(2) Whenever the last syllable of a Singular Noun begins and ends with s such as…
(But we must say Venus's beauty and James's hat where the last syllable only ends with s.)
(3) Whenever the last syllable of a Singular Noun ends with S or CE and the Noun is followed by the word sake such as….
For goodness' sake
Sentences with nouns in The Genitive (or Possessive) Case :
My sister’s son is going to Sweden on a project.
His parents’ bungalow is sold out for a huge price.
Their friends’ certificates were gutted down in the fire accident.
My daughter’s exam comes on next Monday.
Animals’ welfare should be taken care of by the government.