I belong to a linguistic group where members discuss interesting questions about language: word formation, spelling, pronunciation… that is to say, everything related to this amazing world: the world of words.

Recently somebody asked about the correct form of writing a sentence in which an apostrophe was involved, and I realized that this tiny punctuation mark is often difficult to use even for people who usually write in English as it is their mother tongue. One of my colleagues thinks apostrophes are pesky because people don’t know how to use them; while another thinks the problem is that there isn’t an agreement on how to use them.

Let’s start with a definition: the Collins English Dictionary defines an apostrophe as the mark () when it is written to indicate that one or more letters have been left out of a word, as in “isn’t” [= is not] and “we’ll” [= we will]. It is also added to nouns to form possessives, as in “Mike´s car”. The Merriam Webster Dictionary defines it as a mark () used to indicate the omission of letters or figures, the possessive case, or the plural of letters or figures.

We can say apostrophes are used for these reasons:

1. Missing letters. There seems to be agreement on the use of apostrophes to replace letters in contracted forms of be, have, modals, between “n” and “t” in contracted forms with not, in the first person plural imperative, and when the word is never written in full.

I’m (= I am) terribly sorry.

I’ve (= I have) no idea.

I’d (= I would) like to talk with you.

I can’t (= can not) see a thing.

Let’s (= let us) have a drink.

I was at the office at seven oclock (= of the clock)

I have recently recovered from a bout of  flu (= influenza)

(People nowadays usually write “flu” without the apostrophe, as in “phone”.)

2. Possessives. There is also an agreement on the use of apostrophes in front of an “s” added to a noun or pronoun, or after a plural noun ending in “s”, to show a relationship such as possession.

Mike’s car.

Charles’s wife. (Note that “Charles” ends in “s” but as it is a singular noun the correct possessive mark is ‘s but… you can find the form Charles’ too; it’s just a style choice.)

My parents’ house.

[Warning: It is not correct to use an apostrophe in front of the “s” of the possessive pronouns yours, hers, ours and theirs, or the possessive determiner its.]

3. Special plurals. Words which do not usually have plurals sometimes have an apostrophe when a plural form is written.

I got three A’s on the exams.

That song is from the 90’s. (You can also find ’90s and 90s here.)

It was a great idea, but there were a lot of if’s.

Then, where is the problem? It is not correct to use an apostrophe and an “s” to form a plural, but people often get into a muddle with this. You can find in coffee shops, in business meetings or at schools signs like “Place dirty mug’s on the tray”; “All team member’s should turn in proposals on Thursday”; “Parent’s, please sign up to bring something for the class party”(*).

So this is the key: It is not correct to put apostrophes in normal plurals. And an inspiring song to finish…

(*Examples taken from the Chicago Tribune article “Apostrophe’s lament“).

[Note: For clarity reasons I have used double inverted commas instead of simple ones when needed in this article.]