Follow these guidelines:
Use an apostrophe to show that someone or something in a group of words ‘owns’ something in the same groups of words.
Rule 1: If the ‘owner’ word ends in the letter s, simply add an apostrophe to the end of the word:
- Dr Jones’ report is due today.
- James’ report is excellent.
- The boys’ results (more than one boy) are poor.
If you feel there should be another s, because of the way the owner word sounds when spoken, add an apostrophe and an s. James’ report sounds perfectly okay, but Ross’ report sounds as if it needs another s (Ross’s report). In cases like these it’s okay to use an apostrophe and an s, rather than an apostrophe alone. Be consistent. If you use Ross’s report one time in a document, use it every time.
Rule 2: If the owning word ends in a letter other than s, add an apostrophe and an s (’s) to the end of the word:
- Sally’s appointment is at 3 pm.
- The committee’s decision is final.
Rule 3: If there are two or more owners, add the apostrophe to the last owner only:
- David and Jane’s project report.
- Mr Smith and Ms Jones’ account is overdue.
But, if there are multiple independent owners, use apostrophes for all of them:
- David’s and Jane’s project reports.
- Mr Smith’s and Ms Jones’ accounts are overdue.
Rule 4: Don’t add apostrophes to the pronouns his, hers, its, ours, yours or theirs, because these words already imply ownership:
- Its colour is fading.
- The papers are ours.
- The figures are hers.
Rule 5: Apostrophes are disappearing from the names of streets, places, brands, businesses and other organisations. Check if you’re unsure.
- State Teachers College.
- Kings Cross.
- Diners Club.
Rule 6: Singular references to time have an apostrophe, but plural references don’t:
- One week’s notice.
- Two weeks notice.
- One day’s leave.
- Three months leave.
Use an apostrophe to indicate that a word is a contraction (a joining together) of other words:
- I’ve for I have.
- She’s for she is.
The apostrophe is usually placed at the point marking the missing letters, but watch out for irregular contractions, such as shan’t from shall not and won’t from will not.
Don’t use apostrophes in abbreviations (QCs, GPs, PhDs) or with numbers (1980s, four 10s) unless needed to avoid confusion (e.g. the class of ’84).
Use an apostrophe to avoid confusion in groups of lower case letters:
- Mind your p’s and q’s.
- Dot your i’s and cross your t’s.
Don’t put an apostrophe in its unless you mean it is (or it has).
- It’s a difficult task.
- Its value is limited.
Don’t use an apostrophe in ordinary plurals. Ever.
- Cabbage’s $2 X
- Egg carton’s X