The grammar quesiton I probably get asked most frequently is this one:
“If you use an apostrophe to show possession – such as ‘John’s shirt’ or ‘mother’s new hairdo’ – why not in “its” – for example, ‘The dog chewed it’s bone’?
Well the answer is that it would be too confusing. In addition to denoting possession, an apostrophe is also used to denote a contraction – ie, that one or more letters are missing. For example: ‘It’s a nice day’ means ‘It is a nice day’.
So, ‘The dog chewed it’s bone’ means ‘The dog chewed it is bone’ – which doesn’t make a whole lot of sense.
Get more great grammar tips in The Grammar Cookbook