Apostrophes can be used in two ways—to show possession and to indicate omission.
Apostrophes Used to Show Possession
The rules of grammar require that an apostrophe be used to form both singular and plural possessive nouns.
Singular Possessive Nouns
Use an apostrophe followed by an s when you form the possessive of a singular noun.
Ex: the cat’s litter box, the dog’s owner, the professor’s study guide
In each of these cases, the noun (cat, dog and professor) is singular, meaning that there is only one of each. The apostrophe s is used to indicate ownership.
|The Whose Test: If in doubt about whether a word is possessive or not, ask yourself whose litter box?, whose owner?, or whose study guide? These questions are key indicators that imply ownership. By answering to whom the item belongs, you have just revealed the noun to be possessive and required an apostrophe.|
Regular Plural Possessive Nouns
A plural noun that ends with the letter s requires an apostrophe after the s to show possession.
Ex: the cats’ litter box, the dogs’ owner, the professors’ study guides
In the examples above, the s after each word indicates that there are more than one cat, more than one dog and more than one professor. The apostrophe following the s indicates possession.
The best way to determine the differences between singular and plural possessive nouns is illustrated in the following chart:
|Singular Nouns||Singular Possessive||Plural Nouns with s||Plural Possessives with s|
Irregular Plural Possessive Nouns
Some nouns are irregular in their plural form. They do not merely add an s to their singular forms to create the plural. Nouns such as man, woman, and child change in their spelling to men, women and children. In these cases, an apostrophe followed by an s is needed.
Ex.: the men’s room, the children’s playground, women’s apparel.
There are a few common errors that appear in students' writing. To see these common mistakes, visit Common Possessive Pronoun Mistakes.
Some proper names ending in an s cause many problems for writers. Determining if there should be an apostrophe s or an s apostrophe depends on if the name is plural or singular, or if there is a pattern of repeated s sounds.
Singular Possessive Proper Nouns ending in s
Here, there is only one person having ownership, Charles Dickens and Charles.
Charles Dickens Charles In Charles Dickens's novel Charles's network
The Continuous S
The rule of grammar states that if a name has more than one syllable and ends in an s, and the last syllable makes an /ez/ sound (like in Texas), then only an apostrophe is needed.
Moses Jesus Socrates Texas Moses' book Jesus' glass Socrates' view Texas' law
Apostrophes Used to Show Omission
An apostrophe is needed when making contractions in order to take the place of omitted letters.
|do not||don't||they are||they're|
|should not||shouldn't||I would||I'd|
Although these are common practice in our everyday writing, contractions are sometimes viewed suspiciously formal writing.
An apostrophe is required if part of the year is omitted.
Ex: I love the ‘80s. The ‘60s was an era of great musical influence.
An apostrophe is not required to form the plural of a number.
Ex.: In the 1950s
He scored in the 1500s on his SATs.
An apostrophe is not needed to form the plural of abbreviations
Ex.: CDs SATs PHDs
Some grammar guides also state that an apostrophe is no longer required to form the plurals of letters.
Follow the recommendations of the publication manual (MLA or APA) concerning apostrophes used to form plurals of letters.
You can test your understanding of this handout by completing Student Success Center exercises available here.