Yes, Someone else’s is correct if you are talking about an object that belongs to another person.
That coat isn’t mine. It is someone else’s.
We use the apostrophe s to show possession.
What does “someone else’s” mean?
We use “someone else’s” when something belongs to a person but we don’t know who that person is.
We usually use someone else’s when the object is offered to the wrong person and we want to show that the object belongs to a different person.
I don’t know who owns the car. It is not John’s car so it must be someone else’s.
Someone else vs Someone else’s difference
“Someone else’s” means that another person owns something. “Someone else” just means “another person”.
Is that Peter?
No, it is someone else.
Is that Peter’s house?
No, it is someone else’s.
Someone or someone else difference?
“Someone” means another person that we don’t know.
“Someone else” means another person that we don’t know but not the first person.
Can someone please open the door?
Someone else Example:
No, I don’t want John to open the door.
Can someone else open the door?.
In the example for “someone”, it doesn’t matter who opens the door. When we include “else”, the first option is incorrect.
“Else” is a common term in computer programming for this purpose. It is used to show the computer what to do if the first solution doesn’t work.
Someone’s or someone else’s?
When we add the apostrophe s, we just add possession.
We either add the noun or if the noun is already mentioned in a previous sentence it is not necessary.
This has to be someone’s car. Is it yours?
No, This is someone else’s car. (It is not mine)
Someone else’s in conversation
I hate cooking, can’t someone else do it?
No, You have to cook for yourself sometime!
This beer is not mine. It must be someone else’s. Oh well.