The negative short form of the verb to be: How and When to Use in English

She is not a star ➝ She's not a star. She's not is the short form of she is not.]Use the short form in spoken language and informal situations. Example: she's not Canadian / she isn't Canadian.

Lisa and Sean are not from abroad ➝ Lisa and Sean aren't from abroad. They aren't 
is the short form of they are not. Note: you could also say they're not. Example: they're not from Hawaii / they aren't from Hawaii.

I am not cold ➝ I'm not cold. I'm not is the short form of I am not. Note: the subject I only has one short form. Example: I'm not okay with this.

Shorty isn't the hotel porter, with isn't (short for is not), which is the negative short form of the verb to be that we use for subjects such as he, she and it (Shorty = he). Generally speaking, we use isn't (or 's not) after the name of a person, animal, object or place. Example: the hotel's not in the city centre / the hotel isn't in the city centre.

You could say, for example, they aren't hotel porters, with aren't referring to the subject they, and not to he (= Shorty) as in the original sentence.

The form ’m not follows the subject I , not the name of a person like Shorty. Example: I’m not ready!

They're not American guests. After they, the negative short form of the verb to be is ’re not. Note: you could also say aren’t To be, present simple, negative, short. Example: they're not Lucy and Mark and they aren't from London.

You can use isn't when the subject is he/she/it or after a name, but not after they. Example: Mr. Obama isn't an Australian guest.

You can use ’m not after the subject I, but not after they. Example: I’m not Irish.

I’m not tired. This is the short negative form that we use after the subject I. Example: I'm not an expert in this field.

You can say she's not happy or he's not Luke, but you cannot use ’s not after the subject I.

’re not follows subjects like we, you or they, not I. Example: we’re not in Bath at the moment.

Caroline isn't the hotel's chef, with isn't , which is the short negative form of the verb to be that you use after the name of a person like Caroline (= she). Note: you could also say Caroline's not the hotel's chef. Example: Magda isn't a kind receptionist / Magda's not a kind receptionist.

I'm not 35 years old is how you tell someone that 35 is not your age using the negative short form of the verb to be To be, present simple, negative, short. Example: I'm young. I'm not 95 years old.

You aren't alone. The negative short form of the verb to be To be, present simple, negative, short that we use after the subject you (both singular and plural) is aren't (or ’re not). Use the verb to be before an adjective (here alone) to describe people, animals or objects. Example: you aren’t tall / you’re not tall.