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Lesson 4

Relative Clauses: Adding Details to Sentences

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Hello! Welcome to the fourth lesson in our grammar module.

In our last lesson, we focused on using different verb forms to talk about the future. We're continuing our work on building grammatical range and accuracy, which is essential for achieving a high score on the IELTS exam.

Today's learning outcome is to construct sentences using relative clauses (who, which, that) to add information. This is one of the most effective ways to move from simple sentences to the more complex structures that examiners look for in the IELTS Writing and Speaking sections. By the end of this lesson, you'll be able to connect ideas smoothly and add precise detail to your sentences.

1. What is a Relative Clause?

A relative clause is a part of a sentence that gives more information about a noun. Think of it as a multi-word adjective. It usually begins with a relative pronoun like who, which, or that.

Combining simple sentences using relative clauses makes your writing more fluent and academic.

Simple: The student is from my country. The student won the scholarship.
Complex: The student who won the scholarship is from my country.

This image breaks down the basic structure:

Understanding Relative Clauses
This diagram shows how a relative clause provides more information about a noun ("the cat") and contains its own subject ("Toby") and verb ("saw").

2. Choosing the Right Pronoun: who, which, that

The first step is choosing the correct pronoun. The basic rules are straightforward:

  • who is for people.
  • which is for things and ideas.
  • that can be used for both people and things, but it's often less formal than who or which.

Let's watch a short video that introduces these pronouns and explains how they work.

RELATIVE PRONOUNS | RELATIVE CLAUSES | ADJECTIVE CLAUSES - who, which, that, whose, whom

This video from Arnel's Everyday English provides a great overview of the main relative pronouns and how they relate to the noun they are describing.

Watch from 01:38 to 02:57. Pay close attention to the chart the speaker uses to show which pronoun to use for people, things, and animals.

Here are some examples relevant to your studies:

  • The professor who teaches anatomy is highly respected.
  • The dental instrument which is used for scaling teeth is called a scaler.
  • This is the research paper that I was telling you about.
Test your understanding!

Combine the two simple sentences into one sentence using who, which, or that.

  1. A patient came to the clinic. The patient had a severe toothache.
  2. The university has a new library. The library contains thousands of medical journals.
  3. I spoke to a dentist. The dentist specializes in oral surgery.
Show answer
  1. The patient who/that came to the clinic had a severe toothache.
  2. The university has a new library which/that contains thousands of medical journals.
  3. I spoke to a dentist who/that specializes in oral surgery.

3. The Most Important Rule: Defining vs. Non-Defining Clauses

This is the most crucial concept for using relative clauses correctly. The difference depends on whether the information in the clause is essential or just extra detail.

  • Defining Relative Clauses: Provide essential information that identifies which person or thing we are talking about.

    • No commas are used.
    • You can use who, which, or that.
    • Example: The textbook that I borrowed from the library is due back today. (The clause is essential; it tells us which textbook).

  • Non-Defining Relative Clauses: Provide extra, non-essential information. The sentence still makes sense without it.

    • They are separated by commas.
    • You can use who or which, but you cannot use that.
    • Example: My professor, who has published several books, is an expert in periodontics. (The clause is extra information; we already know who the professor is).

This distinction is vital. Getting the commas right will significantly improve your grammatical accuracy score in IELTS Writing. Let's watch a detailed explanation.

RELATIVE PRONOUNS | RELATIVE CLAUSES | ADJECTIVE CLAUSES - who, which, that, whose, whom

Let's return to the video from Arnel's Everyday English. The next section explains the difference between defining and non-defining clauses very clearly.

Watch from 02:57 to 08:59. Focus on: The concept of 'necessary' vs 'optional' information. The critical rule about using commas for non-defining clauses. The rule that you cannot use 'that' in a non-defining clause.

This chart provides a great summary of the rules we've just covered.

Defining vs. Non-Defining Relative Clauses
This grammar chart clearly compares the rules for defining and non-defining clauses, highlighting the differences in comma usage and pronoun choice.

A special use of which: In non-defining clauses, which can also refer to the whole idea of the sentence before it. This is very useful in academic writing.

  • The clinical trial was stopped early, which surprised the research community. (Here, "which" refers to the entire event of the trial being stopped).
Test your understanding!

For each sentence, decide if the relative clause is defining or non-defining and add commas if necessary.

  1. My brother who lives in London is a doctor. (I have more than one brother).
  2. My brother who lives in London is a doctor. (I only have one brother).
  3. The research paper which was published last month has attracted a lot of attention.
  4. IELTS which is an English proficiency test is required by many universities.
Show answer
  1. My brother who lives in London is a doctor. (Defining - no commas. The clause is needed to specify which brother).
  2. My brother, who lives in London, is a doctor. (Non-defining - commas needed. The clause is extra information).
  3. The research paper which was published last month has attracted a lot of attention. (Defining - no commas. The clause specifies which paper).
  4. IELTS, which is an English proficiency test, is required by many universities. (Non-defining - commas needed. "IELTS" is a specific name, so the clause is extra information).

4. When Can You Omit the Relative Pronoun?

To make your English sound more natural, especially in the Speaking test, you sometimes don't need the relative pronoun.

Rule: You can omit the relative pronoun (who, which, or that) only when it is the object of a defining relative clause.

  • Subject: The scientist who discovered the vaccine became famous. (You cannot omit who, because 'the scientist' is the subject of 'discovered').
  • Object: The book (that) I am reading is about medical ethics. (You can omit that, because 'the book' is the object of 'I am reading').

Let's see this in action.

RELATIVE PRONOUNS | RELATIVE CLAUSES | ADJECTIVE CLAUSES - who, which, that, whose, whom

The next part of the video explains when you can remove the relative pronoun. This is a key feature of natural-sounding English.

Watch from 10:05 to 12:22. Focus on the difference between the pronoun as the 'subject' vs. the 'object' of the clause.

5. Final Practice and IELTS Connection

Using relative clauses correctly is a sign of a more advanced English user. To connect this directly to your IELTS preparation, let's look at some common mistakes and how to avoid them.

IELTS Grammar: Using That, Who & Which Like a Pro

This article from 'IFI' has a very useful table of common mistakes that IELTS candidates make with relative clauses. Reviewing these will help you avoid them in your own practice.

Read the section titled '4. Common IELTS Mistakes'. The table clearly shows the error, explains why it's wrong, and provides the correction.

Conclusion

Excellent work today. You've learned a powerful tool for making your sentences more complex and academic. By mastering relative clauses, you can express your ideas with greater precision and fluency.

Key Takeaways:

  • Use who for people and which for things. that can be used for both in defining clauses.
  • Defining clauses provide essential information, use no commas, and identify the noun.
  • Non-defining clauses provide extra information, must use commas, and cannot use that.
  • You can omit the pronoun in a defining clause if it's the object.

In our next lesson, we will explore adverbial clauses. This will give you another way to construct sophisticated sentences by expressing ideas of time, reason, and contrast, further boosting your skills for the IELTS exam.