How to Understand Relative Clauses

Imagine trying to describe something incredibly specific without the right words, like painting a detailed portrait but only having broad strokes available. You’d miss nuances, leave out crucial information, and ultimately, your message would be incomplete. This is often the frustration people encounter when their writing or speech lacks the precision that relative clauses provide. More than just a grammatical rule, relative clauses are powerful tools that allow us to add detail, clarify meaning, and create richer, more informative sentences. They are the scaffolding upon which complex ideas are built, enabling us to pinpoint exactly who, what, which, or where we are talking about. Without them, our language would be clunky, repetitive, and surprisingly vague. This comprehensive guide will demystify relative clauses, transforming them from a confusing concept into a readily accessible and highly actionable skill for any English speaker or learner.

The Core Function: Adding Information and Avoiding Repetition

At their heart, relative clauses are adjectival. This means they function like adjectives, modifying a noun or pronoun. However, instead of being a single word, they are a group of words that contain a subject and a verb, and they relate back to a noun or pronoun in the main clause. Their primary benefit is efficiency. Consider these two sentences:

The dog barked loudly.
The dog was brown and shaggy.

To combine them without a relative clause, you might say: The brown, shaggy dog barked loudly. While effective for two simple sentences, imagine if you had many more details. A relative clause streamlines this: The dog, which was brown and shaggy, barked loudly. Here, “which was brown and shaggy” acts as a compact, informative package describing “the dog.”

Deconstructing the Components: Relative Pronouns and Adverbs

The key to connecting a relative clause to the main clause lies in special words called relative pronouns and relative adverbs. These words serve a dual purpose: they act as a conjunction, linking the two clauses, and they also function as a grammatical element within the relative clause itself (a subject, object, or adverbial modifier).

Relative Pronouns:

Who/Whom: Used for people. “Who” is subjective (acts as the subject of the relative clause), and “whom” is objective (acts as the object of the verb or preposition in the relative clause).
- Subject: The woman who called me works at the bank. (Who is the subject of “called”)
- Object: The man whom I met yesterday was very kind. (Whom is the object of “met”)
- Object of Preposition: The person to whom you sent the letter has moved. (Whom is the object of “to”)
- Actionable Tip: When in doubt between “who” and “whom,” try substituting “he/she” for “who” and “him/her” for “whom.” If “he/she” works, use “who.” If “him/her” works, use “whom.”
Whose: Possessive, used for people or things. It indicates ownership or close association.
- The artist whose paintings are in the gallery is my friend. (Whose indicates the paintings belong to the artist)
- I saw a car whose tires were flat. (Whose indicates the tires belong to the car)
Which: Used for things, animals, or ideas.
- The book which I read was fascinating. (Which refers to “the book”)
- The cat, which was purring loudly, rubbed against my leg. (Which refers to “the cat”)
That: Can be used for people, things, animals, or ideas. It is often interchangeable with “who” or “which” in certain contexts (specifically, restrictive clauses), but has its own distinct functions.
- The car that is parked illegally will be towed. (That refers to “the car”)
- She is the student that won the scholarship. (That refers to “the student”)

Relative Adverbs:

These are less common but equally powerful, indicating place, time, or reason.

Where: Refers to a place.
- This is the house where I grew up. (Where indicates the place)
- We visited the city where the Olympics were held. (Where refers to the city)
When: Refers to a time.
- I remember the day when we first met. (When indicates the day)
- There was a time when I believed anything. (When refers to the time)
Why: Refers to a reason.
- Do you know the reason why he left? (Why indicates the reason)
- That’s why I didn’t come to the party. (Why refers to the reason, though often implied)

The Great Divide: Restrictive vs. Non-Restrictive Clauses

Understanding the distinction between restrictive and non-restrictive relative clauses is paramount. This difference affects punctuation, meaning, and even the choice of relative pronoun.

1. Restrictive (Defining) Relative Clauses:

Function: These clauses provide essential information that is necessary to identify or define the noun or pronoun they modify. If you remove a restrictive clause, the meaning of the main sentence changes significantly or becomes ambiguous. They restrict the meaning of the noun to a specific entity.
Punctuation: They are NOT set off by commas.
Relative Pronoun Choice: “That” can be used for people or things. “Who” for people, and “which” for things. In many cases, “that” is preferred for things in restrictive clauses, though “which” is also grammatically correct. The relative pronoun or adverb can often be omitted if it functions as the object of the verb in the relative clause.
Examples:
- The student who studied diligently passed the exam. (If you remove “who studied diligently,” you don’t know which student passed. The clause defines the student.)
- I live in the house that has a red door. (Removes ambiguity; distinguishes this house from others.)
- This is the book (that) I told you about. (Here, “that” is the object of “told you about” and can be omitted.)
- He visited the town where his grandparents were born. (The “where” clause specifies which town.)

2. Non-Restrictive (Non-Defining) Relative Clauses:

Function: These clauses provide additional, non-essential information about the noun or pronoun they modify. The main sentence’s meaning remains clear even if the non-restrictive clause is removed. They simply add extra detail or commentary.
Punctuation: They ARE set off by commas (or a single comma if at the end of the sentence). Think of the commas as parentheses, indicating extra information.
Relative Pronoun Choice: ONLY “who/whom,” “whose,” “which.” “That” cannot be used in non-restrictive clauses. The relative pronoun or adverb CANNOT be omitted.
Examples:
- My brother, who lives in New York, is visiting next week. (I only have one brother, so “who lives in New York” just adds extra information; the sentence is clear without it.)
- The Eiffel Tower, which is in Paris, is a famous landmark. (We know which landmark; the clause adds a geographical detail.)
- Her new car, which she bought last month, is very sleek. (The fact that it was bought last month is extra information about the already identified car.)
- April 15th, when taxes are due, is a stressful day for many. (The clause just adds context to a specific date.)
Actionable Tip: If you can remove the clause and the sentence still makes perfect sense, use commas and avoid “that.” If removing the clause makes the sentence confusing or changes its meaning, no commas are needed, and “that” is an option. This is the single most important rule to internalize.

The Art of Omission: Reduced Relative Clauses

Sometimes, a relative clause can be shortened or “reduced” while still conveying the same meaning. This creates more concise and elegant sentences, particularly in written English.

A relative clause can be reduced when:

The relative pronoun is the subject of the relative clause AND the verb is a form of “be.”
- Original: The man who is standing next to the car is my uncle.
- Reduced: The man standing next to the car is my uncle.
- Original: The book which was written in 1980 is now a classic.
- Reduced: The book written in 1980 is now a classic.
The relative pronoun is the subject, and the verb is active. The relative clause is replaced with a present participle (-ing form).
- Original: The students who attend this university are very bright.
- Reduced: The students attending this university are very bright.
The relative pronoun is the object (in a restrictive clause), and the relative pronoun and auxiliary verb (if any) are omitted.
- Original: That’s the car (that) I bought last week.
- Reduced: That’s the car I bought last week. (Here, the pronoun “that” was already optional, but this highlights how it’s completely gone.)

Actionable Tip: Reduction is a high-level skill that improves fluency and conciseness. Practice identifying “who is,” “which was,” “that is,” patterns for easy reduction.

Common Pitfalls and How to Avoid Them

Even seasoned speakers make mistakes with relative clauses. Awareness is half the battle.

“Who” vs. “Whom”: As discussed, this is a perpetual challenge. Use the “he/him” test. The person whom I spoke to (I spoke to him). The person who spoke to me (He spoke to me).
“Which” vs. “That” in Restrictive Clauses: While often interchangeable, a common stylistic preference (especially in American English) is to use “that” for restrictive clauses referring to things and “which” only for non-restrictive ones. While not a strict rule, adhering to this can make your writing clearer for some readers. The crucial point is that “that” cannot be used in non-restrictive clauses at all.
Comma Usage with Non-Restrictive Clauses: Forgetting the commas makes a non-restrictive clause appear restrictive, completely changing the meaning.
- The students who passed the exam celebrated. (Only the students who passed celebrated.)
- The students, who passed the exam, celebrated. (All the students passed the exam, and all of them celebrated.)
Omitting the Relative Pronoun When it’s the Subject: This is a definite no-no.
- Incorrect: The man lives next door is a doctor.
- Correct: The man who lives next door is a doctor. (Who is the subject of “lives” and cannot be omitted.)
Incorrect Pronominal Agreement: Ensure the pronoun in the relative clause agrees with the antecedent in number.
- Incorrect: The dog, who was wagging their tail, seemed happy. (Dog is singular, so “their” should be “its.”)
- Correct: The dog, which was wagging its tail, seemed happy.
Dangling Relative Clauses: Less common, but ensure the clause clearly modifies the intended noun.
- Awkward: I saw a dog in the park with a shiny collar, which was barking loudly. (Was the park barking loudly?)
- Correct: I saw a dog with a shiny collar in the park, which was barking loudly. (The dog was barking.) Or better: I saw a dog in the park that had a shiny collar and was barking loudly.

Beyond the Basics: Advanced Applications and Nuances

Mastering the fundamental types of relative clauses opens the door to more sophisticated sentence structures and expressive capabilities.

Prepositional Phrases within Relative Clauses: Sometimes, a relative pronoun can be the object of a preposition. The preposition can be placed before the pronoun or at the end of the clause. While both are grammatically correct, placing the preposition at the end is more common in informal spoken English, whereas placing it before the pronoun is more formal.
- Formal: This is the book about which I was speaking.
- Informal: This is the book which/that I was speaking about. (Note: “That” is acceptable here because it is a restrictive clause.)
- Formal: The person to whom you gave the gift is my cousin.
- Informal: The person who/whom/that you gave the gift to is my cousin.
Non-Restrictive Clauses Modifying Entire Clauses (Sentential Relative Clauses): A non-restrictive “which” clause can sometimes refer to the entire preceding clause, not just a single noun. This is a powerful way to add a comment or explanation about a whole idea.
- She won the lottery, which surprised everyone. (Here, “which” refers to the entire act of her winning the lottery, not just “the lottery” itself.)
- He arrived late, which was typical of him. (Refers to the act of arriving late.)
Elliptical Relative Clauses (Advanced Omissions): Sometimes, in very informal or telegraphic speech, an entire relative clause (especially a restrictive one whose pronoun is the object) can be almost entirely implied.
- “The pizza I ordered was delicious.” (Implied: The pizza [that] I ordered was delicious.)
- “The report he wrote was excellent.” (Implied: The report [which] he wrote was excellent.)
Punctuation Nuances with Restrictive Clauses that End with a Preposition: When a restrictive relative clause ends with a preposition and could precede a non-restrictive clause, careful punctuation is required.
- The person I looked up to, who eventually became my mentor, was instrumental in my career. (Here, “who eventually became my mentor” is non-restrictive information about the single person that I looked up to.)

The Path to Mastery: Practice and Conscious Application

Understanding relative clauses isn’t about rote memorization; it’s about recognizing patterns and consciously applying rules to enhance clarity and precision.

Reading Actively: As you read, pay close attention to sentences containing “who,” “whom,” “whose,” “which,” “that,” “where,” “when,” and “why.” Identify the relative clause, the noun it modifies, and whether it’s restrictive or non-restrictive. Notice the punctuation.
Deconstruction Exercises: Take complex sentences and break them down into their main clause and any relative clauses. Then, try to combine simple sentences using relative clauses.
- Original: The woman is a doctor. She lives next door.
- Combined: The woman who lives next door is a doctor.
Rewriting for Conciseness: Practice reducing relative clauses or rephrasing sentences to make them more concise while maintaining clarity.
- Original: The car which was parked illegally was towed.
- Rewritten: The car parked illegally was towed.
Self-Correction in Writing: As you write, pause and ask yourself:
- Can I combine these two sentences using a relative clause?
- Does this information define or just add extra detail? (This determines comma usage.)
- Am I using “that” correctly? (Only for restrictive clauses, only for things/people depending on context.)
- Have I made the relative pronoun or adverb agree with its antecedent?
- Is the relative pronoun functioning as a subject or object within its clause?

Conclusion: Empowering Your Expression

Relative clauses are not mere grammatical curiosities; they are essential building blocks for sophisticated, nuanced communication. They allow you to paint vivid pictures with your words, leaving no room for misunderstanding about which person, what thing, where something happened, or when it occurred. By internalizing the distinction between restrictive and non-restrictive clauses, understanding the roles of relative pronouns and adverbs, and practicing the art of reduction, you unlock a powerful capability: the ability to express complex ideas with precision and elegance. This mastery will not only improve your written and spoken English but also enhance your ability to comprehend detailed information, leading to more effective and impactful communication in all aspects of your life. The journey from confusion to clarity with relative clauses is a rewarding one, directly impacting your confidence and competence in the English language.