Apostropheguide.com

The apostrophe is one of the most frequently misused punctuation marks in English language. The apostrophe serves two main purposes, marking letters missed out to shorten words (contractions); and to show possession.

Marks letters that have been omitted

Example: it’s -> it is; there’s -> there is; wouldn’t -> would not

An apostrophe can be used to remove letters from two words being joined together, typcially a vowel in a pronoun or the words ‘has’ or ‘us’ although other instances exist. The apostrophe in this case replaces the letters missed out.

‘It’ can never be possessive, it can only mean ‘it is’.

Question to ask yourself: Would an apostrophe replace missing letters?
If yes, insert an apostrophe.

Shows possession

Example: the dog’s bone; the man’s phone
But: the Jones’ house

Apostrophes can be used to show possession. In the above examples, the bone belongs to the dog and the phone belongs to the man. If the noun (thing) in the sentence does not end in an s, then an ’s is added to show the possesion. If the noun is plural or ends in an s, simply adding an apostrophe is sufficient.

Question to ask yourself: Would an apostrophe be used to show possession?
If yes, insert an apostrophe.