Relative Clauses in English: A Complete Grammar Guide

Relative Clauses in English are an essential part of English grammar. They help learners connect ideas, provide additional information, and make sentences more precise and natural. This grammar point frequently appears in school tests, English proficiency exams, and everyday communication.

Understanding relative clauses involves learning how to use relative pronouns, distinguish between defining and non-defining relative clauses, and shorten clauses without changing their intended meaning.

In this guide, you will explore the fundamental rules of Relative Clauses in English, examine practical examples, review common mistakes, and complete exercises with answers to strengthen your grammar skills.

What Are Relative Clauses in English?

A relative clause is a dependent clause that modifies a noun or pronoun in a sentence. It provides information that helps identify a person, thing, place, time, or reason, or adds extra details about it.

Relative clauses commonly begin with relative pronouns such as who, whom, which, that, and whose, or relative adverbs such as where, when, and why.

Consider the following examples:

• The girl who is wearing a red dress is my sister.
• This is the restaurant where we had dinner.
• I like the book that you recommended.

In these sentences, the bold clauses describe the nouns that come before them. They help readers understand exactly which person, place, or thing the speaker means.

Relative clauses are particularly useful because they allow you to combine related ideas into a single sentence instead of writing several short, disconnected sentences.

Relative Clauses in English: Grammar Rules and Formulas

To use Relative Clauses in English correctly, you need to identify the noun being modified and choose a relative pronoun or adverb that matches its grammatical function.

A common structure is:

Noun + relative pronoun/adverb + subject + verb + additional information

For example:

• The woman who works at the bank is my aunt.
• The laptop which I bought yesterday is very fast.
• The city where I was born is beautiful.

The structure of the relative clause depends on whether the relative word functions as a subject, object, or possessive expression, or indicates a place, time, or reason.

Relative Pronouns in English

Relative pronouns connect a relative clause to the noun it describes. The most common ones are who, whom, which, that, and whose.

Important grammar notes:

• Use who when the relative pronoun is the subject of the clause.
• Use whom when referring to a person as the object in formal contexts. In everyday English, who is also commonly used as an object pronoun.
• Use that in defining relative clauses, but not in non-defining relative clauses.
• Use whose before a noun to express possession.

Examples:

• The teacher who explains the lesson clearly is popular with students.
• The man whom we invited arrived early.
• The computer that stopped working belongs to my brother.
• The girl whose father is a doctor studies at my school.

Relative Adverbs: Where, When, and Why

Relative adverbs provide information about a place, time, or reason. They often replace a longer expression involving a preposition and a relative pronoun.

You can remember these words by associating where with places, when with times, and why with reasons.

In certain contexts, relative adverbs can be replaced by a preposition followed by which.

For example:

• The house where I live is small.
• The house in which I live is small.

Both sentences express the same basic idea.

Types of Relative Clauses in English

Relative clauses are generally divided into two categories: defining relative clauses and non-defining relative clauses. Understanding the difference helps you choose the correct relative pronoun and use punctuation appropriately.

Defining Relative Clauses

A defining relative clause provides essential information about a noun. Without this information, the reader may not know exactly which person or thing the sentence refers to.

Example:

The students who study hard often get good grades.

The phrase who study hard identifies the group of students being discussed.

Key characteristics include:

• No commas are used to separate the clause from the noun it modifies.
• Relative pronouns such as who, whom, which, that, and whose may be used, depending on the sentence.
• The relative pronoun can sometimes be omitted when it functions as an object and the grammatical conditions are satisfied.

More examples:

• The book that you gave me is interesting.
• The people who live next door are friendly.
• The restaurant which opened last month is already popular.

In each example, the relative clause helps identify the intended person, object, or place.

Non-Defining Relative Clauses

A non-defining relative clause adds extra information about a person, thing, or place that is already identified. The additional information is not essential for identifying the noun.

Example:

My father, who works in a hospital, enjoys reading.

The speaker has already identified the person as their father. The clause who works in a hospital simply provides additional information.

Key characteristics include:

• Commas separate the relative clause from the main sentence.
• That cannot replace who or which in a non-defining relative clause.
• The relative pronoun cannot normally be omitted.

More examples:

• London, which is the capital of the United Kingdom, attracts many tourists.
• Anna, whose brother studies abroad, speaks English fluently.
• My laptop, which I bought last year, still works well.

Quick tip: If the clause is necessary to identify the noun, it is usually defining. If it simply adds information about an already identified noun, it is usually non-defining.

Reduced Relative Clauses in English: Three Common Forms

Reduced relative clauses make sentences more concise while retaining their essential meaning. The three common forms use V-ing, past participles (V3/V-ed), and infinitives with to.

Not every relative clause can be reduced in the same way. You should check the meaning, verb form, and grammatical structure before making a change.

Reducing Relative Clauses with V-ing

Use V-ing when the relative clause has an active meaning and the noun performs the action.

Basic pattern:

Noun + who/which/that + verb → Noun + V-ing

When the clause contains a form of be, the relative pronoun and the be verb can usually be omitted.

Examples:

• The girl who is standing near the door is my cousin.
• The girl standing near the door is my cousin.

Another example:

• The man who works in this office is friendly.
• The man working in this office is friendly.

In these examples, the person performs the action, so the V-ing form is appropriate.

Reducing Relative Clauses with V3/V-ed

Use a past participle when the relative clause has a passive meaning. The noun receives the action rather than performing it.

Basic pattern:

Noun + who/which/that + be + V3/V-ed → Noun + V3/V-ed

Examples:

• The house which was built in 1990 is still in good condition.
• The house built in 1990 is still in good condition.

Another example:

• The documents that were sent yesterday have arrived.
• The documents sent yesterday have arrived.

The reduced form keeps the passive meaning while removing unnecessary words.

Reducing Relative Clauses with To-infinitives

An infinitive with to is commonly used after expressions such as the first, the second, the last, the next, and the only. It can also appear in certain structures involving superlatives or an intended action.

Common pattern:

Noun + the first/the last/the only/the next + to-infinitive

Examples:

• She was the first student who answered the question.
• She was the first student to answer the question.

Another example:

• He is the last person who will leave the room.
• He is the last person to leave the room.

These structures are especially useful in formal writing and grammar exercises. However, the infinitive should only be used when the intended meaning and sentence structure support the reduction.

Common Mistakes When Using Relative Clauses in English

Even when learners understand the basic rules, they may make mistakes involving relative pronouns, punctuation, or reduced clauses.

Using That in a Non-Defining Relative Clause

Incorrect: My mother, that is a teacher, loves reading.

Correct: My mother, who is a teacher, loves reading.

In a non-defining relative clause, use who or which as appropriate instead of that.

Omitting a Relative Pronoun That Functions as a Subject

Incorrect: The boy plays football is my brother.

Correct: The boy who plays football is my brother.

The relative pronoun cannot simply be omitted when it functions as the subject of the clause. If the structure allows it, you may reduce the clause instead:

The boy playing football is my brother.

Using Commas Incorrectly

Consider these two sentences:

• My sister who lives in Da Nang is a doctor.
• My sister, who lives in Da Nang, is a doctor.

The first sentence suggests that the clause identifies which sister is being discussed. The second treats the clause as additional information about an already identified sister.

Choosing the correct punctuation depends on the intended meaning and context.

Confusing Who and Whom

Use who when the relative pronoun functions as a subject:

The woman who called me is my teacher.

Use whom when it functions as an object in formal English:

The woman whom I called is my teacher.

In everyday communication, who is also widely accepted as an object pronoun in many contexts.

Relative Clauses in English: Practice Exercises with Answers

The following exercises will help you apply relative pronouns, distinguish clause types, and practise reducing relative clauses. Try completing each activity before checking the answers.

Exercise 1: Combine the Sentences Using Relative Pronouns

Combine each pair of sentences into one sentence using an appropriate relative pronoun or adverb.

• The man is a doctor. He lives next door.
• I bought a laptop. It is very fast.
• The woman was friendly. I met her yesterday.
• The student is absent today. His father is a teacher.
• The film was exciting. We watched it last night.

Exercise 2: Reduce the Relative Clauses

Rewrite each sentence by reducing the relative clause where appropriate.

• The boy who is playing basketball is my brother.
• The books which were written by Nam are popular.
• She was the first student who answered the question.
• The people who are waiting outside will be served soon.
• The car that was damaged in the accident belongs to my uncle.

Exercise 3: Choose the Correct Answer

Select the correct option to complete each sentence.

Question 1: The woman _____ teaches us English is very kind.

1. which
2. who
3. where
4. whose

Question 2: This is the restaurant _____ we had dinner last week.

1. where
2. who
3. whose
4. whom

Question 3: My brother, _____ lives in Hanoi, is visiting us this weekend.

1. that
2. where
3. who
4. whom

Question 4: The documents _____ yesterday are on my desk.

1. sending
2. sent
3. send
4. which sending

Question 5: Peter was the first person _____ the question.

1. answer
2. answering
3. answered
4. to answer

Answer Key and Explanations

Exercise 1

• The man who lives next door is a doctor.
• I bought a laptop which is very fast.
• The woman whom I met yesterday was friendly.
• The student whose father is a teacher is absent today.
• The film which we watched last night was exciting.

Explanation: Who commonly functions as a subject referring to a person. Which refers to things, whom functions as an object referring to a person, and whose indicates possession.

Exercise 2

• The boy playing basketball is my brother.
• The books written by Nam are popular.
• She was the first student to answer the question.
• The people waiting outside will be served soon.
• The car damaged in the accident belongs to my uncle.

Explanation: Sentences one and four use V-ing because the clauses have active meanings. Sentences two and five use past participles because they have passive meanings. Sentence three uses a to-infinitive after the first student.

Exercise 3

• Question 1: B. who — refers to a person and functions as the subject of the relative clause.
• Question 2: A. where — refers to the place where the dinner took place.
• Question 3: C. who — introduces a non-defining relative clause that provides additional information about the speaker’s brother.
• Question 4: B. sent — the past participle expresses the passive meaning of the reduced clause.
• Question 5: D. to answer — the to-infinitive is used after the first person.

Mastering Relative Clauses in English will help you connect ideas more effectively, improve your reading comprehension, and write clearer sentences. Regular practice with relative pronouns, punctuation, and reduced clauses will gradually make these structures easier to recognise and use.

Frequently Asked Questions About Relative Clauses in English

Where Do Relative Clauses Appear in a Sentence?

Relative clauses usually appear immediately after the noun or pronoun they modify. They can occur in the middle of a sentence or at the end, depending on the position of the noun. This placement helps readers understand which person or thing the additional information describes.

When Can You Omit a Relative Pronoun?

A relative pronoun such as who, whom, which, or that can often be omitted when it functions as the object in a defining relative clause. It cannot normally be omitted when it functions as the subject. Relative pronouns in non-defining relative clauses must also be retained.

Do Defining Relative Clauses Need Commas?

Defining relative clauses do not use commas because their information is necessary to identify the noun. Non-defining relative clauses, by contrast, are separated by commas because they provide additional information about an already identified person, place, or thing.

What Are the Main Types of Reduced Relative Clauses?

The three common forms use V-ing for active meanings, V3/V-ed for passive meanings, and a to-infinitive in suitable structures such as those following the first, the last, or the only. The correct form depends on the grammatical structure and intended meaning.

Keywords:

• Relative Clauses
• Defining Relative Clauses
• Non-defining Relative Clauses
• Reduced Relative Clauses
• Relative Pronouns in English