Apostrophes for abbreviation

Might be worth saying, if you want to see about apostrophes for possession, go to April 15th 2008. This is the one about the other use for apostrophes...

...and it's actually really simple: the apostrophe is just put in in place of some missing letters. Sometimes we want to merge two words together to make it easier to say or read something. For example, instead of saying do not go there we might say don't go there. In this example, and in most examples, nothing changes about the original words other than a letter is missed out and the words are squashed together into one word. Sometimes more than one letter is missed out and very occasionally there are changes to the spelling of the original words*. Here are some examples of the change:

do not...donot...don't
must not...mustnot...mustn't
have not...havenot...haven't
It is...itis...it's
cannot...(no merge - one word already)...can't
I will...Iwill...I'll
would have...wouldhave...would've
will not...willnot...won't*

The blue letters are the ones that get missed out and replaced with an apostrophe.

You will notice that I have included it's in the list above. Only put an apostrophe in the word 'its' if you are saying 'it is' in a shortened way. That is all you need to know. If you are saying 'its' to mean that something belongs to 'it' you DO NOT need an apostrophe. Here are some correct examples:

Its main advantage is that it goes faster.
Its tyres are bald.
It's a shiny red car.