Introduction
The apostrophe is used to indicate possession (e.g., Tom’s plan, the cat’s whiskers) and to show the omission of letters where a word has been contracted (e.g., I can’t remember the ’80s for I cannot remember the 1980s). In some rare cases an apostrophe can be used to form a plural.
Possession
Apostrophes are used to show that a noun or pronoun is in the possessive case. In other words, one thing belongs to another:
Sinbad’s adventures
the constitution’s detractors
a mouse’s tail
the cabin’s porthole
the incumbent’s election strategy
One way to check if you’re dealing with possession is to turn the phrase into an “of” construction:
Sinbad’s adventures = the adventures of Sinbad.
This test also helps us to figure out where the apostrophe goes. When I rewrite the parents of those kids as those kids’ parents, I add the apostrophe after the actual word in the possessive case (not kid’s, but kids’).
Unfortunately, using an of construction works less well when the relationship between nouns is more abstract. This is especially the case when indicating time or quantity:
tomorrow’s agenda
a summer’s day
anyone’s game
a week’s pay
a dollar’s worth
However, if you understand the basic idea of possession, then these outliers will provide little trouble.
Basic rules
Here are the basic rules to show possession.
1. For singular nouns, add ’s:
Eugene’s apple
the tree’s branches
Chris’s homework
2. The same rule applies to plural nouns that don’t end in s:
the children’s toys
the women’s washroom
the moose’s migration
3. However, for plural nouns that end in an s you only have to add the apostrophe:
the horses’ pasture
the siblings’ secrets
the dolphins’ tricks
Tricky cases
Singular nouns that end in s
Most of the time, if a singular noun ends with an s (or sounds like it does) you can safely add the apostrophe and the s:
James’s car
the sax’s mouth-piece
the bus’s colour
the glass’s contents
However, there are a number of exceptions to this rule. In such cases you are encouraged to add only an apostrophe. Although style guides disagree about the details, here are the most common exceptions.
1. When the noun ends with an “us” or “eez” sound:
Jesus’ parables
Socrates’ suicide
Moses’ suspicions
2. When you’re dealing with biblical or classical names (note the overlap with 1):
Euripides’ play
Barnabas’ mission
3. In some for … sake expressions where the noun ends with an s (or sounds like it does):
for conscience’ sake
for goodness’ sake
However, this is not an iron rule for nouns that only sound like they end with an s (e.g., you can write appearance’s sake or appearance’ sake).
4. With nouns that end in s and don’t change their form from the singular to the plural:
many TV series’ ratings (my favourite series’ lead actor)
those species’ survival (that species’ habitat)
5. With names of places, organization, and the like:
The United States’ foreign influence
Step Up For Students’ scholarships
Please remember, though, that these are not hard and fast rules. Grammarians argue a great deal about when you can drop the s and add only the apostrophe. For example, in academic writing the trend is to retain the s after the apostrophe, whereas news publications are more likely to drop it.
If in doubt, you could use an “of” construction instead: the parables of Jesus, etc. This can also makes your writing sound more formal.
Compound Terms
When multiple words are combined in one unit it’s called a compound noun. The apostrophe is added to the last word, even if the compound noun is a plural:
the Governor General’s approval
my sisters-in-law’s holiday plans
everybody else’s homework
my mother-in-law’s criticisms
the commander-in-chief’s cowardice
Group Ownership
Group ownership, or “joint possession,” occurs when something belongs to multiple nouns.
When people own something together, only one apostrophe is needed:
Jerry and Jessica’s dairy farm could be seen from the highway.
When there is no common ownership, you need separate apostrophes:
We admired Elsa’s and Jaspreet’s ultrasounds.
Double Possessives
A double possessive is a phrase that indicates possession twice (by using of and ’s):
a daughter of Mary’s
a painting of Esther’s
If this sounds awkward, just remember that you would say a daughter of mine (where mine is a possessive pronoun) and not a daughter of me. These constructions are typically avoided in formal and academic writing.
Contraction
In addition to indicating possession, apostrophes show when letters or numbers are omitted. In the case of verbs, the shortened forms sometimes look quite different from the original (the worst offender being ain’t):
don’t = do not
it’s = it is
won’t = will not
William’s late = William is late
shouldn’t = should not
ain’t = am not; are not; is not
Other words can also be shortened using apostrophes:
ne’er-do-well
will-o’-the-wisp
Apostrophes sometimes show missing numbers:
she grew up in the ’90s (for the 1990s)
we used to own a ’97 Pontiac Montana (for 1997)
In academic writing, contractions are typically written out fully (if the revolutionaries had not … instead of hadn’t). By contrast, the use of slang is often indicated by means of apostrophes (how y’all doin’?).
Finally, in some names the apostrophe appears to indicate a contraction but is actually used to indicate pronunciation, or to tie words together. For example, the apostrophe in the Irish name O’Neill does not indicate omitted letters, because O is an anglicized version of the Gaelic ua, or descendant.
Forming plurals
Normally you should not use the apostrophe to form the plural of a noun. Such a mistake is called “the grocer’s apostrophe,” because of its common occurrence on signs and advertising.
However, an exception is made for the plurals of numbers, letters, symbols, and words referred to as words:
Dot your i’s and cross your t’s
He can count by 1’s and 2’s.
She likes to use &’s in her writing
There are no if’s and but’s about it
(Note that in these cases italics are not used for the apostrophe and the s).
This rule is not applied rigorously though, and in some cases (especially abbreviations) it may be preferable to omit the apostrophe:
Not all PhDs imply high IQs
In fact, in the plural form of decades it is now customary to leave out the apostrophe:
Gutenberg invented his printing press in the late 1430s.
Common errors and ambiguities
It’s / its
If you’re confused about these two, don’t be embarrassed. People often assume that it’s is possessive because the possessive case is typically formed with an ’s. However it’s is a contraction for it is, whereas its shows possession:
It’s almost bedtime. (It is)
The plane made its descent.
A cow chews its cud.
It’s me, silly. (It is)
Place names and businesses
If you like to scour maps, you’ll notice that a lot of place names have dropped their apostrophes. This is especially the case in the US, where the apostrophe is the exception rather than the rule. Thus we have Martha’s Vineyard (which got its apostrophe back in 1933), but also Harpers Ferry. Similar irregularities occur with company names. Compare, for instance, Barclays Bank and Shoppers Drug Mart with Wendy’s or McDonald’s.
Nouns as adjectives
In English, nouns often take on the role of adjectives (e.g., the school play, tunnel vision), in which case there is no need for an apostrophe to indicate possession (not the school’s play or tunnel’s vision). However, in some cases it is difficult to know whether you’re dealing with possession or not:
Is it farmer’s market, farmers’ market, or farmers market? (comp. teacher’s college)
Each version has a slightly different ring. The apostrophe suggests more that the market is owned by the farmers, whereas the adjective form clarifies what kind of market it is. None of these versions is necessarily incorrect, and you will have to balance your own preference with local usage.
Possessive pronouns:
Make sure you don’t use an apostrophe for the following possessive pronouns:
hers, its, theirs, yours, and ours.
On the other hand, indefinite pronouns do take an apostrophe:
one’s, somebody’s, etc.
Last names
Never use an apostrophe for the plural of names. Just add an s or es. The latter is used when the name ends with an s or a similar sound (sh, ch, x, or z):
The Joneses and the Larches played shinny on the frozen pond.
There are three Eriks in Wayside School.
Also, don’t change a final y to ies:
The Trotskys taught the Tracys that sharing is caring.
So when you add the apostrophe to show possession, it looks like this:
The Nguyens’ restaurant was vandalized.
The Smiths’ Lego collection fills the entire basement.