There are only two cases of nouns in English: possessive case and common case.
English nouns have only two cases: Possessive Case where nouns take the special ending; and Common Case where nouns don’t have any ending.
The Common case is the form in which the noun is given in the dictionary.
English nouns in the Common case can be used in the functions of the subject and direct complement (always without a preposition), an indirect and prepositional complement, an attribute (usually with or without a preposition).
Possessive case of singular nouns is formed by adding the /’s/ ending to the noun:
the girls‘s hat
the cat‘s leg
Possessive case of plural nouns is formed just by adding an apostrophe:
the boys‘ book
the girls‘ bags
If a plural noun is formed by changing its form and not by adding the /s/ ending, the possessive case is formed like with the singular noun, i.e. by adding the /’s/ ending:
the children‘s books
The possessive noun plays only one function – an attribute (individual characteristics of the defined word):
The use of English nouns in the possessive case:
1. For the expression of the object’s belonging
the student’s pen
The important thing to remember is that common nouns are general names. Thus they are not capitalized unless they begin a sentence or are part of a title.
Man, mountain, ocean
The student recognized the teacher.