You can use apostrophes in two main ways – to indicate a contraction or to show ownership. (Although please note that proper nouns, such as Methodist Ladies’ College, retain their own apostrophes.)
Use an apostrophe to replace omitted letters in a word.
Use an apostrophe to indicate that a noun owns something.
Singular nouns take an’s, even if the noun ends with s.
Lynne Truss’s book
Plural and collective nouns not ending in s also take an ’s.
the fish’s offspring
Plural nouns that end with s have an apostrophe added after the s.
the students’ work
the lecturers’ seminars
If the ‘possessive’ belongs to more than one person, only add an apostrophe to the last person in the grouping.
Smith and Maynard’s book about Bob Brown
Unless Smith and Maynard have written separate books, in which case it would read:
Smith’s and Maynard’s books about Bob Brown
Note that both ‘bachelor’s degree’ and ‘master’s degree’, when used in a generic sense, require an apostrophe.
While some dislike this convention, it is prescribed by the Macquarie Dictionary (the Australian standard) and the Oxford English Dictionary (the UK standard), and aligns with our key institutional partner Warwick University. Currently you will find the terms used both with and without an apostrophe throughout our online and print publications – gradually, we need to move toward correct usage.
When not to use apostrophes
Do not use apostrophes to indicate the plural. Just add the s. So remember, there are no apostrophes in the plural form of acronyms.
There is no apostrophe in decades.
There is no apostrophes in adjectival phrases.
Don't usee apostrophes in expressions of time that denote more than one day, week or month, etc.
in six months time
four days work
But if the reference is singular, use the apostrophe.
A month's holiday.
Very occasionally, apostrophes can help clarify expressions, even when they aren't needed.
Dot your i’s and cross your t’s.
There is a difference! 'Its’ indicates possession, whereas 'it's' indicates a contraction and means either 'it is' or 'it has'.
None of the pronouns need an apostrophe to indicate possession, but most change their form. The possessive form of ‘she’, for example, is ‘her’. The pronoun ‘it’ changes to ‘its’ to indicate possession, but, as with the rest of the pronouns, it doesn't need an apostrophe.
her latest book
Don’t use an apostrophe unless the word is being used as an abbreviation for ‘it is’ or ‘it has’.
It’s one explanation = It is one explanation
It’s been a pleasure = It has been a pleasure
Use smart (or curly) apostrophe marks (like ‘this’) rather than straight apostrophe marks (like 'this'). Microsoft Word usually defaults to curly apostrophes, so if you ‘find’ and ‘replace all’, you can convert them.