Apostrophes

The following guidelines apply to possessive nouns:

• Single possessive nouns take an apostrophe before the 's', for example: the teacher's voice, the atlas's size, Fiona's work.
• When singular nouns end in s, the 's is generally used, for example: Dickens's novels, Nurse Jones's uniform.
• An exception occurs in the case of ancient and biblical words, when s' is conventionally used, for example: Pythagoras' theorem, Jesus' teachings.
• Plural possessive nouns that end in 's' take an apostrophe after the 's', for example: the teachers' strike, the atlases' shelf.
• Plural possessive nouns that don't end in 's' take the apostrophe before the 's', for example: the children's books, the mice's tracks.
• Only the last noun in statements of joint ownership take the apostrophe, for example: my mother and father's visit.
• If the ownership is not joint, each noun has the apostrophe, for example: my mother's and father's visits.
• Some Australian place names involving possessives do not take an apostrophe, for example: Kings Cross, Crows Nest, St Marys.

Possessive pronouns do not take an apostrophe, for example the mouse shook its tail, the book is hers.
Common areas to look out for involving apostrophes include:

• saying 1980s (not 1980's)
• differentiating between it's and its.

In relation to apostrophes and time, expressions of time involving a plural reference do not take an apostrophe, for example six weeks holiday, in three months time.
Singular time references do take an apostrophe to help mark the noun as singular, for example a day's work, the year's cycle.
Non-possessive phrases do not take an apostrophe because the plural noun describes rather than indicates ownership, for example Brisbane Girls Grammar School, teachers guide
However, the omission of the apostrophe can sometimes be jarring, so exercise judgment and common sense, for example Children's Book Week.
Generic phrases do not take an apostrophe, for example drivers licence, travellers cheque.
Plurals are not formed by the addition of an apostrophe, for example 1960s, MPs, Carols by Candlelight.