The apostrophe is one of the most misused punctuation marks in the English language, and its misuse is growing. The apostrophe is used for the following reasons:
- in place of a missing letter in contracted words, such as don't instead of do not, it's instead of it is, they're instead of they are, or an omission, such as the year of '66.
- to indicate possession, as in Tom's ball, Descartes's theorem, the judges' rulings. (Note that adding the apostrophe and an extra 's' to a word that already ends in 's' produces a different sound to that when only the apostrophe is added.)
- to indicate possession to the last word in a phrase or a compound – my mother-in-law's couch; the Member for Canberra's vote
- to indicate possession for joint ownership, the apostrophe is added to the last name on the list, for example, John and Mary's anniversary. If the thing is not owned jointly, use an apostrophe for each name, as in John's and Mary's birthday
- the apostrophe is also needed when you want to indicate a duration in time, for instance, in one minute's time…… or after ten year's experience…….
- you will also add an apostrophe to the word before a gerund, for example, In the event of David's resigning…… Note the two separate meanings in the following sentences, just by adding or not adding an apostrophe: I object to the visitor's speaking Italian. I object to the visitors speaking Italian.
- Use the apostrophe with certain plurals, such as do's and don'ts and M.D.'s
Don't use the apostrophe for phrases like one's and two's – this should be ones and twos, or for the '60's – should be the 60s, or the sixties.