The apostrophe is the most commonly misused punctuation mark. There are two uses for apostrophes:
- contractions; and
- possessives
Contractions are words where one or more letters have been omitted. The apostrophe is used in place of the letter(s) that have been removed. Some of the most common examples are:
- it’s (it is, it has)
- we’ll (we will, we shall)
- can’t (cannot)
- won’t (will not)
Contractions can be used in formal writing, but you should use them only rarely as they make writing more chatty.
Some words feature an apostrophe because they were once contracted, but now we only ever use the contracted form:
- o’clock
- Hallowe’en
- ne’er-do-well
Possessives indicate that something belongs to someone. The place of the apostrophe depends on whether the possessor is singular or plural. A singular possessive goes before the possessive 's'; a plural possessive goes after the possessive 's'.
- the revolt's outcome (one revolt)
- the decade's developments (one decade)
- the revolts' outcome (many revolts)
- the decades' developments (many decades)
Some people find it helpful to think of possessive apostrophes as showing something has been left out. The apostrophe takes the place of the missing word.
- the revolt (its) outcome - the revolt's outcome
- the decade (its) developments - the decade's developments
- the revolts (their) outcome - the revolts' outcome
- the decades (their) developments - the decades' developments
- Engels's argument - Engels (his) argument (sometimes, if a name ends in 's' and the possessive 's' sounds clumsy, the possessive 's' is left out, e.g. Engels' argument)
- the class's size - the class (its) size
- the classes' size - the classes (their) size
However:
- the children (their) schooling - the children’s schooling
- the people (their) discontent - the people's discontent
(children and people are plurals, but plurals that don't end in 's' should have a possessive apostrophe placed before the possessive 's')
N. B. the possessive 'its'
The possessive 'its' causes endless confusion with apostrophes. ‘Its’ is the possessive form of ‘it’. It does not need an apostrophe. It operates just like his and hers, which don't take apostrophes:
- its power was unassailable
- it was the predominant theory of its time
- its flaws are apparent
- its qualities are debatable
'Its' takes an apostrophe only when it's a contraction:
- It's difficult to describe its attraction. (It is difficult to describe its attraction.)
The incorrect use of apostrophes irritates markers, mainly because it's really quite easy to get them right.