I have sometimes got confused about the apostrophe myself. It’s importance should not be underestimated. As I regularly observe that it is often omitted from people’s comments, which looks terrible in my opinion, I thought this explanation and flow chart might offer some guidance. Your feedback to it’s usefulness would be much appreciated.
I have seen articles about apostrophes where some of the comments relating to them have been somewhat derogatory. I have seen comments such as “why all this fuss about using an apostrophe; get a life.”
The thing is apostrophes are very important, not only do they allow the person using them to write in a professional manner; they are an important aspect of communication. 
An analogy would be using a turn signal or indicator while driving a car. If you are driving and the person in front changes lanes without indicating you have no idea of their intent and confusion can ensue. Dangerous on the roads! I agree that leaving out an apostrophe while writing is not life threatening but hopefully the analogy emphasises the importance of correct communication.
Something else to keep in mind, professionalism. How seriously to you want to be taken? How can you critique someone else’s writing when you cannot write yourself?
The apostrophe is an English language communicator which is as important as the full stop (period). It communicates meaning and interpretation to the reader.
Can’t for example is shortening of can not. Cant, on the other hand, has a number of different meanings but is often associated with whining or singsong speech or the associated phraseology of a profession for instance. So as you can see, the inclusion of a little apostrophe can make quite a difference.
There is nothing like a discussion on the correct use of the apostrophe to engender debate and argument, particularly as there are little nuances that can get very confusing. This can be self-defeating as it can make people scared of using them and be open to criticism.
Remember that we all get it wrong sometimes, the point is to try. So here is a basic explanation and a flow chart to visually aid you through the basics.
When to use the apostrophe
The apostrophe indicates either
1. That a letter is missing or
2. Of ownership.
1. Where words are contracted the apostrophe replaces the missing letter. Didn’t is short for did not or it’s is a contraction of it is. The position of the apostrophe is important as it is placed exactly where the letters are missing. The correct placing is didn’t not did’nt for example. This is a common mistake.
2. To show possession or ownership i.e. a word such as ‘accounts’ is owned by another noun eg ‘company’ (as in the company’s accounts) or the student’s file – the apostrophe shows that the file belongs to the student. It is unlikely that a word ending with an apostrophe ‘s’ will be followed by a verb.
Usage in practice.
· There is one exception to the possession rule – you do not put an apostrophe in ‘its’ to show possession – if you did, it would be an abbreviation of ‘it is’.
· If the word is plural and possession is indicated then the apostrophe goes after the ‘s’ . Example: A number of companies’ accounts were examined and then returned to them or all of the students’ files were returned to them.
· If a word ends in ‘s’ as a plural, or it simply ends in ‘s’ eg campus and does not indicate possession, do not put an apostrophe.
· If the word is singular and ends in ‘s’ then normally, to show possession, the apostrophe goes after the ‘s’ to show possession. In this example the campus’ main entrance.
Go through any material that you write and use this check flow chart for every word and ends with the letter S. You might find this laborious but it gives a good feel for the right way to do it and practice makes perfect!

October 21st, 2009 at 5:09 am
An excellent article on using the apostrophe. I used to find this so difficult to make children understand when I was teaching. I should have had a lesson like this to follow. Brilliant work.
Christine
October 26th, 2009 at 5:17 pm
Nice one…
November 1st, 2009 at 5:13 am
I am still waiting to give someone a gold star – who will be first? To try and get the article noticed I have included an error on the very subject I was writing about. There are two errors, in fact, although it’s the same one twice. As a teacher, I have used tricks like this to see if the students are concentrating. So the challenge is – what is the mistake and who will be the first to find it?
November 30th, 2009 at 5:14 pm
OK I give up.. Here is the answer – I refer in my article: “There is one exception to the possession rule – you do not put an apostrophe in ‘its’ to show possession – if you did, it would be an abbreviation of ‘it is’.” Therefore “It’s importance” and “to it’s usefulness” in the first paragraph are wrong. They should not have the apostrophe. Lesson over!