The possessive case shows ownership. With the addition of ’s (or sometimes just the apostrophe), a noun can change from a simple person, place, or thing to a person, place, or thing that owns something. There are a few different ways to form the possessive of a noun. We’ll discuss these ways below.T GRAMMARLY

If the noun doesn’t end with an s, add ’s to the end of the noun. See the following examples:

This is Mary and her dog. The dog is Mary’s pet; Mary is not the dog’s pet.

This is the way to the men’s room.

She got a job in the children’s section of the library.

Do we add another s for the possessive form of a name ending with s? Which is correct, Chris’s chair or Chris’ chair? James’s car or James’ car? Actually, both ways are correct. If a proper name ends with an s, you can add just the apostrophe or an apostrophe and an s. See the examples below for an illustration of this type of possessive noun.

You’re sitting in Chris’ chair.

You’re sitting in Chris’s chair.

Have you seen James’ car?

Have you seen James’s car?

But when you have a plural noun that ends in s, add just the apostrophe. This is also true when you have a proper noun that’s plural.

This is the boys’ bedroom.

My parents’ house is a lovely old one.

Here’s a tip: Should you write student’s or students’?

When you have an ordinary noun like student, you can tell whether the possessive form refers to one student or many students by looking at where the apostrophe is. When you’re talking about one student, add apostrophe + s:

The student’s favorite subject was science.

In the sentence above, we are talking about the favorite subject of one student. When you’re talking about many students, add an apostrophe.

The students’ favorite subject was science.

In the sentence above, we are talking about several students who all share the same favorite subject.

If you have a compound noun (for example, when you’re talking about two people who jointly own one thing), change only the last noun to the possessive. The examples below illustrate this usage of the possessive case.

Mike and Amanda’s new loft apartment is really neat.

Please tell Annie and Mary’s mother that they’ll be late getting home from school.

If the possessor is a building, an object, or a piece of furniture, you don’t need to add an apostrophe to show possession. See the examples below for reference:

The maid cleaned the hotel’s room .

The maid cleaned the hotel room .

We met in the office’s lobby .

We met in the office lobby .

Shut the car’s door.

Shut the car door .

Diferencia con el español

El caso posesivo (también conocido como “genitivo”) indica posesión y no existe en español. En español usamos la preposición “de” para expresar posesión, por ejemplo:

-El nombre de mi hermano es Tim.

Los hablantes del español tienden a escribir esta frase de la siguiente forma:

–The name of my brother is Tim.

La oración anterior no es incorrecta, pero un 99% de los hablantes del inglés usarían el caso posesivo (NO “of”); el cual se compone de: un apostrofe + s: ‘s

-My bother’s name is Tim. (El nombre de mi hermano es Tim)

Estructura:

Si, por ejemplo, queremos decir “El apellido de mi madre es Smith”, debemos ubicar primero el sustantivo o persona que posee (madre / mother) y luego agregar ‘s a ese sustantivo:

-My mother’s name is Smith.

Si queremos decir “El auto de mi profesora es rojo”, agregamos ‘s a la persona o sustantivo que posee, que en este caso es “profesora”:

-The teacher’s car is red.

Diferencia con el verbo “to be”

Es posible que haya una confusión entre el caso posesivo y el verbo “to be”. Observa las siguientes oraciones:

-My father’s name is Michael Cooper (El nombre de mi padre es Michael Cooper)

-My father’s tall and strong. (Mi padre es alto y fuerte)

-Sam’s girlfriend is Argentinian. (La novia de Sam es argentina)

-Sam’s Italian. (Sam es italiano)

La clave para evitar esta posible confusión es entender que después del caso posesivo (‘s) siempre debe haber un sustantivo (name, car, girlfriend, etc.). Esto no ocurre cuando el ‘s es la contracción del verbo “to be”

Aunque el uso de la preposición “of” no es necesariamente incorrecto, lo MEJOR es usar “apostrofe + s” cuando hablemos o escribamos en inglés.