A possessive noun is a word used to designate ownership by a person, place, or thing. For instance, if a person wants to indicate that Sarah owns a house, he can use the name Sarah and an apostrophe and the letter "S" to indicate possession. In such a case, he would write "Sarah’s house" to show possession. This even works in the event that the noun is plural rather than singular. For example, a person can write "the girls' room" to show that the room belongs to the girls.
Possessive nouns take ordinary nouns, which are words that represent people, places, animals, or things, and change them so that they show ownership or possession. This provides people with a simple way of showing to whom or what something belongs. These words can be used to show ownership not only of tangible things, but also of living things and things that do not have a physical form. For instance, a possessive noun can be used to show ownership of not only cars, houses, and clothing, but also of pets, plants, and thoughts.
To form a possessive noun, a person usually adds an apostrophe and the letter "S" to a noun. For instance, a person could write or say something such as "the cats that belong to Henry," but there is an easier and shorter way to accomplish the same thing: he could simply write "Henry's cats." By creating a possessive noun, he can make the same point with fewer words; this often helps to make sentences simpler and less confusing.
Sometimes the creation of possessive nouns becomes a little more complicated, such as when a plural noun is involved rather than a singular noun. A singular noun just needs an apostrophe and an "S," but a plural noun often only needs an apostrophe. For instance, if a person wants to show that two or more teachers have students, he can write "the teachers’ students" rather than "the teachers’s students." If the plural noun does not end with an "S," however, it is still necessary to add the apostrophe and the "S," such as in "men's room."
While the use of possessive nouns may seem simple and easy for some, many people find them confusing. They might add an apostrophe and an "S" when doing so is unnecessary, for instance, or add only an "S" to a noun thinking that doing so shows ownership. Often, it is continued practice that helps people to get a better handle on the correct way to use possessive nouns.