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A2 – B2

The Genitive Case: 's vs Of

Everything you need to correctly choose between 's and "of" to show possession in English, plural possessives, and the double genitive, with exam practice.

📖 Reading time: ~9 minutes ✅ Reviewed by a CELTA-qualified teacher 🎯 Covers A1 to B2

📋 What's in This Guide

  1. 1. Introduction — Two Ways to Show Possession
  2. 2. Quick Summary
  3. 3. The Apostrophe S ('s)
  4. 4. The "Of" Structure
  5. 5. Choosing Between 's and Of
  6. 6. The Double Genitive
  7. 7. Common Mistakes
  8. 8. Exercises
  9. 9. Mini Quiz
  10. 10. Exam Focus — Cambridge, IELTS, SELT
  11. 11. Frequently Asked Questions
  12. 12. Related Grammar Guides
  13. 13. Book a Free Level Test

1. Introduction — Two Ways to Show Possession

English has two main ways to show that something belongs to someone or something: the apostrophe-s ("Tom's car") and the "of" structure ("the roof of the house"). They express the same underlying relationship, but native speakers choose between them based on a fairly reliable pattern, mostly about whether the "owner" is a person or a thing, that many learners never have explained to them directly.

2. Quick Summary

⚡ Genitive Case at a Glance

's (apostrophe s)Usually for people, animals, and time: Tom's car, the dog's bowl, today's news
ofUsually for things, places, and abstract ideas: the roof of the house
Plural nouns ending in -sAdd just an apostrophe: the students' books
Common Mistake"the car of Tom" instead of "Tom's car"

3. The Apostrophe S ('s)

RuleExample
Singular noun: add 'sTom's car, the dog's bowl
Plural noun ending in -s: add only an apostrophethe students' books, my parents' house
Plural noun NOT ending in -s: add 's as normalthe children's toys, the men's coats
Names ending in -s: usually add 's (pronounced)James's book (also acceptable: James' book)
💡
's is for people, animals, and time expressions "Tom's car," "the dog's bowl," "today's news," "a week's holiday." These all use 's naturally because the "owner" is a person, animal, or time reference, this is the strongest, most reliable pattern to remember.

4. The "Of" Structure

RuleExample
Things and objectsthe roof of the house, the cover of the book
Abstract ideasthe importance of education, the beginning of the film
Places (often)the streets of London, the centre of the city

5. Choosing Between 's and Of

Owner TypePreferred StructureExample
Person or animal'sMaria's phone. The cat's tail.
Time expression'sYesterday's meeting. A year's experience.
Organisation or group (often treated like a person)'sThe company's profits. The government's decision.
Thing or objectofThe colour of the car. The end of the road.
Abstract conceptofThe cost of living. The purpose of the meeting.
⚠️
Both are sometimes possible For some nouns, especially places and organisations, both forms are acceptable: "London's streets" and "the streets of London" are both correct, the choice can be about style and emphasis, not strict rule-breaking.

6. The Double Genitive

A less common but genuinely useful structure combines "of" with 's, used to mean "one of several," especially with a demonstrative.

StructureExample
a/that + noun + of + possessive pronoun/name'sa friend of mine (= one of my friends)
that car of Tom's (= that particular car belonging to Tom, among his possessions)

7. Common Mistakes

❌ Incorrect✅ CorrectWhy
the car of TomTom's carA person as the owner needs 's, not "of."
the students book (plural, meant: belonging to multiple students)the students' bookPlural nouns ending in -s add only an apostrophe, no extra "s."
the childrens' toysthe children's toys"Children" doesn't end in -s, so it needs a full 's, not just an apostrophe.
the house's roofthe roof of the houseObjects and things generally prefer "of," not 's, though this isn't a strict rule.

8. Exercises

A. Gap Fill — Complete correctly (8 questions)

1. the car ___ (belonging to Tom)
2. the ___ (children, toys, plural)
3. the ___ (students, books, plural ending in -s)
4. the roof ___ the house.
5. ___ meeting was cancelled. (yesterday)
6. the importance ___ education.
7. a friend ___ mine. (double genitive)
8. James___ book. (James, add correct ending)
Show Answers (A)
1. Tom's car   2. children's toys   3. students' books   4. of   5. Yesterday's   6. of   7. of   8. James's (or James')

B. Multiple Choice (5 questions)

1. the car ___ Tom. (a) of (b) 's
2. the ___ toys. (multiple children) (a) childrens' (b) children's
3. the ___ book. (multiple students) (a) students' (b) student's
4. the colour ___ the car. (a) of (b) 's
5. ___ meeting starts at nine. (a) Today (b) Today's
Show Answers (B)
1.b 2.b 3.a 4.a 5.b

C. Error Correction (4 questions)

1. the car of Tom
2. the students book (plural)
3. the childrens' toys
4. the house's roof
Show Answers (C)
1. Tom's car
2. the students' book
3. the children's toys
4. the roof of the house

D. Freer Practice — Write Your Own Sentences (2 tasks)

1. Write a sentence using 's to show possession by a person.
2. Write a sentence using "of" to describe part of an object or abstract idea.
Show Answers (D)
Model answers will vary. Examples:
1. "Sarah's presentation was excellent."
2. "The purpose of the meeting was to discuss the budget."

9. Mini Quiz

1. the car ___ Tom.

2. the ___ toys. (multiple children)

3. the colour ___ the car.

4. ___ meeting starts at nine.

10. Exam Focus — Cambridge, IELTS, SELT

ExamHow This Is TestedSample Question
Cambridge A2 Key / B1 PreliminaryCorrect apostrophe placement in possessives is directly assessed in the Writing paper's mark scheme."The ___ (student) books were collected." (students')
IELTS WritingAccurate genitive use, especially with plural nouns, affects the Grammatical Range and Accuracy score.Correctly writing "the company's profits" vs "the profits of the company" appropriately.
Trinity GESE/ISE (SELT)Possessive 's comes up constantly when discussing family, friends and daily life."My sister's job is very demanding."

11. Frequently Asked Questions

The grammatical structure used to show possession, mainly through 's (Tom's car) or "of" (the roof of the house).
's is generally preferred for people, animals, organisations and time expressions; "of" is generally preferred for things, objects, places and abstract ideas.
If the plural already ends in -s, add only an apostrophe (the students' books); if it doesn't end in -s, add a full 's (the children's toys).
Usually add 's and pronounce the extra syllable (James's book), though simply adding an apostrophe alone (James') is also widely accepted, especially in British English.
A structure combining "of" with 's, used to mean "one of several": "a friend of mine" means one of my friends, not my only friend.
Yes — possessive 's comes up constantly and naturally when discussing family, friends, colleagues and daily life in conversation.
PunctuationApostrophe rules in full, including contractions DeterminersPossessive determiners like my, your, its PronounsPossessive pronouns like mine, yours General English CoursesBuild every grammar point with expert guidance

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