This page has information about the two uses of apostrophes in English.

Apostrophes in contractions

A contraction is the result of joining two words into one. The apostrophe indicates the place where letters have been removed. Some examples:

  • I will → I'll [ pronoun - modal verb contraction ]
  • He could not → He couldn't [ modal verb - negator (not) contraction ]
  • She does not → She doesn't [ auxiliary verb - negator (not) contraction ]
  • They had → They'd [ pronoun - auxiliary verb contraction ]
  • You must not → You mustn't [ modal verb - negator (not) contraction ]
  • Sally would → Sally'd [ noun - modal verb contraction ]
  • Mary is laughing → Mary's laughing [ noun - auxiliary verb contraction ]

This is not too difficult. One potential problem, however is that the ...'s and ...'d contractions can be expanded in two ways. For example:

  • It's → It is / It has
  • We'd → We would / we had

But in context such contractions are unlikely to be ambiguous. On the other hand, a common error by native speakers is to insert an apostrophe in a word that is not a contraction. For example: the dog has lost it's bone. Or Apple's for sale half price.

Apostrophes in possessives

The second use of apostrophes is to denote grammatical possession (or the genitive case). For example:

  • John's book
  • London's buses
  • the king of Spain's daughter
  • the boys' toys

Many native speakers make errors in the possessive use of the apostrophe. Either they omit it where it is needed, or they misplace it. In the phrase the twin's toys, the apostrophe before the -s indicates that only one of the twins is being referred to. To make it clear that both twins are intended, it has to be the twins' toys.

There seems to be a trend towards omitting the apostrophe in plural noun phrases or place names. For example, I refer to various parts of this resource as Teachers site or Learners site. The famous station in London is called Kings Cross. And a Google search throws up as many hits for Boys High School as Boys' High School.

Apostrophes in plurals

It is clear that the apostrophes in cat's and dog's in the following sentence are wrong:

  • I prefer cat's to dog's.

Cats and dogs are non-possessive plurals and should not have an apostrophe. But this clear rule is often flouted. For example, by shopkeepers who write signs such as:

  • Apple's on sale at half-price today.

This incorrect use of an apostrophe in a non-possessive plural is often called the greengrocer's or greengrocers' apostrophe, as it is claimed to be common in signs on fruit and vegetable stalls. [ Examples ]

But the rule is actually not quite so simple when it comes to the plurals of numbers, dates, letters, abbreviations and acronyms. Which of the following plurals is correct in each case?

  • Problem: The test has two question 3s/3's.
  • The internet began in the 1990s/1990's.
  • Stopping is spelled with two ps/p's.
  • My sister has two PhDs/PhD's.
  • The images on this site are all GIFs/GIF's and JPEGs/JPEG's.

You will see examples of both plural forms, but the general trend is towards omitting the apostrophe in such cases. The exception is when leaving out the apostrophe creates a word that is not intended. For example: There are three as in aardvark.

The Chicago Manual of Style is a good source of advice on the use of apostrophes in such cases as exemplified above.

There are three pages containing various learning activities on the topic of apostrophes on the video lessons index. These pages link to several interactive quizzes on the apostrophe that can also be found in the Writing drop-down menu on the language skills index.