Adjective Clauses: Relative Clauses, Rules and Examples

Overview

An adjective clause is a dependent clause that modifies a noun or pronoun in the main clause. It is called an adjective clause because it performs the same function as an adjective: it describes, identifies, or adds information about the noun it follows. The other name for this structure is a relative clause, which refers to the relative pronouns that typically introduce it: who, whom, whose, which, and that.

The most important distinction within adjective clauses is between defining clauses and non-defining clauses. Defining clauses restrict the meaning of the noun, telling the reader which specific person or thing is meant. Non-defining clauses add supplementary information about a noun already clearly identified. The difference between these two types determines word choice, punctuation, and the logical meaning of the sentence.

How Adjective Clauses Are Formed

An adjective clause begins with a relative pronoun or a relative adverb and contains its own subject and verb. It follows the noun it modifies as closely as possible. Placing other words between the noun and its relative clause can create ambiguity.

The relative pronoun serves two functions: it connects the clause to the noun it modifies, and it plays a grammatical role inside the clause itself, acting as the subject, the object, or the possessive determiner.

Choosing the Correct Relative Pronoun

The choice of relative pronoun depends on three factors: whether the noun refers to a person or a thing, the grammatical role of the pronoun inside the clause, and whether the clause is defining or non-defining.

That can refer to both people and things, but only in defining relative clauses. In non-defining clauses, which replaces it for things and who replaces it for people.

Defining Relative Clauses

A defining relative clause identifies which specific person, thing, or group the noun refers to. Without the clause, the sentence either loses its meaning or refers to a different, unspecified entity. Defining clauses are not separated from the noun by commas.

In defining relative clauses, the relative pronoun can be omitted when it functions as the object of the verb inside the clause.

When the relative pronoun is the subject of the clause, omission is not permitted.

Non-Defining Relative Clauses

A non-defining relative clause adds information about a noun that is already clearly and fully identified. Because the information is supplementary, the clause is separated from the rest of the sentence by commas.

Three rules apply specifically to non-defining clauses. First, that cannot be used: which is required for things and who for people. Second, the relative pronoun cannot be omitted. Third, the commas around the clause are required: removing them changes the sentence from non-defining to defining, which alters its meaning.

The first sentence refers to one specific manager and adds a detail. The second implies there are multiple managers and identifies which one is meant.

Adjective Clauses with Prepositions

When the relative pronoun is the object of a preposition inside the clause, the preposition can appear at the end of the clause (informal) or before the relative pronoun (formal).

In formal written English, placing the preposition before the pronoun is preferred. In this construction, whom must be used for people and which for things. That is not used after a preposition.

Defining vs. Non-Defining: A Side-by-Side Comparison

Common Mistakes to Avoid

Mistake 1: Using That in a Non-Defining Clause

That is reserved for defining relative clauses. Using it in a non-defining clause is a grammatical error in standard written English.

Mistake 2: Omitting the Relative Pronoun When It Is the Subject

The relative pronoun can be omitted only when it acts as the object of the clause. When it is the subject, it must remain.

Mistake 3: Missing Commas in Non-Defining Clauses

Without commas, a non-defining clause reads as a defining clause, which changes the meaning of the sentence and can introduce ambiguity.

Mistake 4: Using Whom as the Subject of the Clause

Whom is the object form of who. Using it as the subject of the relative clause is a grammatical error.

Mistake 5: Placing the Adjective Clause Too Far from Its Noun

An adjective clause should follow its noun as directly as possible. When other words separate the clause from its noun, the sentence becomes ambiguous.

Practice Exercises

Exercise 1: Choose the Correct Relative Pronoun

Complete each sentence with the correct relative pronoun: who, whom, whose, which, or that.

1. The researcher ___ conducted the study published her findings last month.
2. The building ___ the meeting is held has no air conditioning.
3. This is the proposal ___ the committee approved unanimously.
4. The client, ___ account has been active for ten years, requested a review.
5. The committee ___ reviewed the application met twice before reaching a decision.
6. The report, ___ was thirty pages long, was submitted ahead of schedule.

Exercise 2: Defining or Non-Defining?

Label each sentence as containing a defining (D) or non-defining (ND) relative clause. Add commas where required.

1. The policy that was introduced last year has already been revised.
2. The head of department who joined from a rival firm restructured the division.
3. His first book which won three awards was translated into twelve languages.
4. The team that finished the project early received a commendation.
5. The warehouse where all inventory is stored is located outside the city.
6. Professor Tan whose research focuses on urban planning will lead the session.

Exercise 3: Correct the Error

Each sentence contains one error related to adjective clauses. Rewrite it correctly.

1. The consultant, that redesigned the process, reduced costs by fifteen percent.
2. The candidate whom was selected for the role declined the offer.
3. The equipment installed by the engineers needs immediate replacement.
4. The documents were sent to the legal team that required urgent review.
5. The head office, which located in the capital, oversees all regional branches.

Summary

Getting the defining and non-defining distinction right, choosing between who and whom accurately, and placing commas only where they belong are the three skills that produce precise, accurate use of adjective clauses.