What the s' form shows
The possessive form shows a relationship between an owner and a person, animal, place, or object. In the phrase the students' books, the owners are several students, and the objects are books.
An apostrophe after the plural -s helps show that there is more than one owner. The exact relationship comes from the context: it may be ownership, belonging, shared use, or an association with a group.
The students' books are on the table.
The students' books are on the table.
Students — several owners; the apostrophe comes after the plural s.
My parents' house is near the park.
My parents' house is near the park.
Parents is already plural, so we add only an apostrophe.
Structure: plural first, then the apostrophe
First form the regular plural: student → students. Then, if this plural already ends in -s, put an apostrophe after the s: students → students'. After the possessive form, name what is connected with the owners: students' desks.
Do not add another s after the plural s. The forms students's and parents's are incorrect in this meaning.
regular plural owner ending in -s + ' + possessed noun
- noun —
- A word naming a person, thing or idea: student, book, happiness.
The teachers' room is upstairs.
The teachers' room is upstairs.
Teachers ends in -s, so only an apostrophe comes after it.
The dogs' bowls are by the door.
The dogs' bowls are by the door.
Dogs is a regular plural; the possessive form dogs' comes before bowls.
Plurals ending in -es and -ies
The rule applies not only to words that simply add -s. If a regular plural is formed with -es or -ies and ends in the letter s, the apostrophe also comes after the final s.
Therefore, class → classes → classes', and baby → babies → babies'. It is important to look at the complete plural form, not only the singular form.
The classes' projects are on the wall.
The classes' projects are on the wall.
Classes is a regular plural ending in -es; we add an apostrophe after the s.
The babies' toys are in the box.
The babies' toys are in the box.
Babies ends in s, so the possessive form is babies'.
The number of owners and the number of objects
The owner's ending tells us how many owners there are, but it does not determine how many objects there are. The girls' room may be one shared room, while the girls' bikes may be several bicycles.
Choose the form of the following noun according to the meaning of the situation. Do not automatically make it plural just because there is more than one owner.
The sisters' café is open.
The sisters' café is open.
There are several owners, but there is one café, so café remains singular.
The visitors' bags are here.
The visitors' bags are here.
There are several owners and several bags; both nouns are plural for different reasons.
Contrast with nearby forms
For one owner, use 's: the girl's bike. For several regular owners whose plural ends in -s, use only an apostrophe: the girls' bikes.
Irregular plurals without a final -s follow a different rule: children's books, men's shoes. These forms are grammatical, but they belong to a related topic; do not form childrens'.
The girl's bike is blue.
The girl's bike is blue.
Girl — one owner, so the apostrophe comes before s.
The girls' bikes are blue.
The girls' bikes are blue.
Girls — several regular owners, so the apostrophe comes after s.
The children's books are new.
The children's books are new.
Children is an irregular plural without a final s, so 's is needed here; this is outside the current rule.
Where the apostrophe goes
The apostrophe is part of the owner word and comes immediately after the plural s, with no space: players'. The noun naming the related thing comes next: players' bags.
The straight mark ' and the typographic mark ’ perform the same function. Both are acceptable in ordinary answers; if an exercise specifically asks for a straight apostrophe, follow that visible requirement.
Here the apostrophe shows a possessive relationship. It does not mark omitted letters, as in the contractions it's or they're, and it does not create an ordinary plural.
The players' bags are by the door.
The players' bags are by the door.
The apostrophe is attached to players, and bags names the players' things.
The nurses' office is on the left.
The nurses' office is on the left.
Nurses' is a plural possessive form; it is not a contraction.
How to apply the rule in your own sentence
Ask three questions: who is connected with the thing, is there one owner or more than one, and does the complete plural end in -s? If there are several owners and the answer to the last question is yes, add only an apostrophe.
Then check the order: the owner in the possessive form comes before the name of the thing. A form with belong to can also be grammatical, but in an exercise that explicitly asks you to practise s', you must use the possessive form.
These are my friends' keys.
These are my friends' keys.
Several friends → friends; the plural ends in s → friends'.
The customers' orders are ready.
The customers' orders are ready.
The phrase briefly says whose orders are ready and keeps the natural word order.
Common mistakes
Incorrect:The students's desks are clean.
Correct:The students' desks are clean.
Students is already a plural ending in -s, so only an apostrophe is needed after the s.
Incorrect:My parents house is near the park.
Correct:My parents' house is near the park.
An apostrophe is needed after the plural parents for the possessive relationship.
Incorrect:The girls's bikes are outside.
Correct:The girls' bikes are outside.
Girls means several girls and already ends in s; the additional s is unnecessary.
Incorrect:The teachers's room is upstairs.
Correct:The teachers' room is upstairs.
The regular plural teachers forms the possessive with one apostrophe after the s.
Incorrect:The babies's toys are in the box.
Correct:The babies' toys are in the box.
Babies is a regular plural ending in -ies that ends in s; the form babies's is incorrect.