English Grammar Rules & Mistakes: Learn All of the Essentials: Writing, Speaking, Literature and Punctuation Rules Complete with 10 Key Skills and Over 200 Common Error Examples

Know when to divide and conquer: understanding apostrophes
The apostrophe is a multitalented punctuation mark. It can own everything
and cut you out of the deal in an instant. Confused, don’t worry. I will
explain what I mean right now.
I am very excited for my sister’s wedding.
First off let’s talk about owning it all. To do that you need an apostrophe as it
is the most common method to show possession, meaning that you or
someone else owns something. In the example above, the person is excited
about going to their sister’s wedding. We know it is the wedding of their
sister because there is an ‘s after the word sister. 
You will be pleased to know that in English, there is only one way to show
that something is possessive and that is to add an ‘s. So as long as you add
this, you won’t go too wrong.
I am very excited about my sister Jessica’s wedding.
That being said, you may falter off track when trying to position the
possessive when a few more words are added to the mix. In the above
example, the possessive apostrophe has switched to the word Jessica and is
no longer on the word sister. That is because it wouldn’t make sense to stay
on the word sister as it would suggest that the sister owns Jessica rather than
Jessica owning her wedding. If you get confused, say it out loud and you will
probably catch the mistake. Concentrate on who owns who.

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This isn’t anything to do with you.
Now comes the taking everything away from you part - or rather, taking
everything away from the words. The above example showcases apostrophes
being used in contractions. As you have heard me say before, we love to
speed up our language. This has resulted in us shortening two words into one
and using a contraction apostrophe to fill in the gaps. The word isn’t is a
contraction of is not. 
There are lots of examples of contractions that we use regularly, such as
don’t, you’re, hasn’t, I’d, etc. Despite using them frequently, we all have a
tendency to mess them up a bit and put the apostrophe in the wrong place.
More often than not the apostrophe is placed before the last letter replacing
vowel sounds in the second word. Commonly, people place it between the
two contracted words, for example, do’nt and would’nt. Remember, the
apostrophe is meant to replace missing letters so in the case of don’t it is
replacing the o in not.
There we are, it’s finally time to leave.
The dog thinks its bed is the sofa.
As we wrap up apostrophes, it’s about time we solved the ultimate
apostrophe mystery: what is the difference between it’s and its. You know
that English is the language of exception and this is no exception, well,
except it is an exception! When coming to deciding how to deal with the case
of it’s and its, it was a bit tricky for grammar theorists. The words it is had
long been shortened to it’s and so was already in common usage. However, it
is a pronoun that can have a possessive and if it followed the possessive rule
should add ‘s to the end of it. However, it’s was already taken as a
contraction so it was finally settled that its was to be used as the possessive.
To work out which to use, ask yourself does the sentence say it is something
or is it talking about owning something. Once you answer this, you will know
the correct form to use.

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