NB It’s odd and a perpetual source of error that the letter ‘s’ is used for plurals and also to denote possession.
It is NOT used to indicate a plural, nor is it used for decoration. The plural of TV is not TV's.
And that's it- Simple but there are a number of sound-alike words, which cause complications.
EXAMPLES of 1. Possessive
The bone belonging to the dog: the dog’s bone
The coat that belongs to Jack: Jack’s coat.
The remote working the TV- The TV's remote
(pedantically this could also mean "the TV is some distance away.")
In a plural word ending in ‘s’ the possessive apostrophe goes after the ‘s’.
The dog’s bone -a single dog
The dogs’ bones -more than one dog.
In a word that happens to end in s an extra s can be added and is usually pronounced. Though for reasons of practicality there may be exceptions.
Davy Jones' locker or Davy Jones's locker
octopus’s or octopus’ garden -single octopus
octopuses’ garden - multiple octopuses
Examples of 2. missing letters
I am - I’m We are - we’re
You are - You’re She is - She’s
He is - He’s They are - they’re
It is - It’s
could not- couldn’t is not - isn’t
was not - wasn’t
Shall not - Shan't Lewis Carroll pointed out that logically it should be sha''n't.
4 of the clock -4 o' clock
that is- that's
Complications and sound-alikes.
There are a group of words, which I will call possessive adjectives (I think this is the correct term), which are possessive in their own right and do not need an apostrophe, some need a qualifying noun, some don’t. Here they are in bold
My dog- He’s mine (he is mine) Your dog- he’s yours
Her bitch- She’s hers His dog - He's his
Its bone- it’s its (dog referred to as ‘it’ for illustrative purposes)
Our dog- it’s ours Their dogs - They’re theirs
(It’s interesting to speculate about the history of these words. Did they originally have an apostrophe? Was mine originally me’s? Was his originally he’s? We need a linguistic historian).
Here we can see some considerable potential for confusion.
Note the differences between you’re and your and their and they’re
And the classic error: its and it’s.
It can be argued that the only use for the apostrophe is for a missing letter. Although much of our vocabulary is Latinate, our grammar is Teutonic. The German language utilises 'es' or 's' for possession as in Gottes Wille (God's will). Middle English and hence Chaucer also frequently used 'es'. for possesion, as in Goddes love. However, we have dropped the 'e', which appears to have been replaced with an apostrophe.
sensibly in German they do not usually use 's' or 'es' for a pleural. The most common plural is 'e'.
Fun with apostrophes
pig's fly - a porcine parasite
Can you think of a sentence containing: its, it's, their, and they're?
for more info: dreaded apostrophe