Using Relative Clauses — I can use relative clauses and common linking words (that, which, who) at an introductory level to add detail.

Every language has strategies for combining shorter thoughts into longer, more informative sentences, and in English the relative clause is one of the most versatile of those strategies. The idea of embedding one clause inside another to modify a noun has been a feature of English since its earliest recorded forms, evolving in structure and usage across centuries of literary, legal, and everyday communication. Understanding the history of relative clauses helps us appreciate why modern English relies so heavily on words like who, which, and that to build complex meaning efficiently.

The central question that this lesson addresses is a practical one: how can an intermediate English learner use relative clauses to move beyond short, choppy sentences and produce writing and speech that sounds natural, cohesive, and information-rich? By the end of this lesson, you will be able to identify relative clauses, choose the correct relative pronoun, and embed additional detail inside your sentences with confidence.

A relative clause is a dependent clause that modifies a noun—called the antecedent—by providing additional information about it. The clause is introduced by a relative pronoun (who, which, or that), which serves as a linking word that connects the main clause to the modifying clause. Because a relative clause cannot stand alone as a complete sentence, it always depends on the main clause for its full meaning, functioning much like an adjective that has been expanded into a clause.

Notice in the diagram above that the relative clause does not stand alone; it splits the main clause into two halves. The first half introduces the antecedent ("The student"), then the relative clause (who passed the exam) inserts itself to add detail about that student, and finally the second half of the main clause ("celebrated with friends") completes the thought. This pattern—main clause part one, then relative clause, then main clause part two—is the most common structure for subject-position relative clauses in English. When you read or hear a sentence with a relative clause, your mind temporarily "pauses" on the antecedent, absorbs the extra information, and then returns to the main action of the sentence.

From Two Sentences to One

The fundamental operation behind a relative clause is sentence combining. You begin with two independent sentences that share a common noun, and you merge them by replacing the repeated noun in the second sentence with the appropriate relative pronoun. Consider these two sentences: (1) "I met a woman." (2) "The woman speaks five languages." Because both sentences refer to the same person (woman), you can replace "The woman" in the second sentence with who and embed it after "woman" in the first sentence: "I met a woman who speaks five languages." The result is a single, cohesive sentence that communicates both pieces of information.

Choosing the Right Relative Pronoun

Subject vs. Object Position

The relative pronoun can function as either the subject or the object of the relative clause, and this distinction affects word order. When the relative pronoun is the subject of the relative clause, it is immediately followed by a verb: "The teacher who explains clearly is popular." When the relative pronoun is the object of the relative clause, a new subject appears between the pronoun and the verb: "The teacher that students admire is popular." In object-position clauses, that can often be omitted entirely in spoken and informal written English ("The teacher students admire"), though keeping it in is never wrong and improves clarity for many readers.

Relative clauses fall into two broad categories that differ in how essential the embedded information is to the meaning of the sentence. Understanding this distinction is important because it affects punctuation and pronoun choice—two areas where even advanced learners sometimes stumble. A defining (restrictive) relative clause identifies or restricts the antecedent; without it, the listener would not know which noun is being discussed. A non-defining (non-restrictive) relative clause adds extra, parenthetical information about an antecedent that is already clearly identified; removing it does not change which noun is meant.

The practical implication of this distinction is straightforward: if the relative clause is essential to identifying the noun, do not use commas and feel free to use that. If the antecedent is a proper noun, a unique thing, or is otherwise already clearly identified, place commas around the relative clause and use who or which—never that. Mastering this comma rule alone will noticeably improve the professionalism of your academic writing.

Let us work through a complete example of transforming two simple sentences into one richer sentence using a relative clause. Suppose you are writing an email to a colleague and you have these two short sentences:

Even when learners understand the concept of relative clauses, certain recurring mistakes can undermine clarity. The table below catalogues the most frequent errors that intermediate learners make, explains why each one is problematic, and offers a corrected version. Studying these patterns will help you self-edit more effectively.

The three relative pronouns you have learned in this lesson—who, which, that—form the foundation for a much larger family of relative structures in English. As your proficiency grows, you will encounter additional relative pronouns and adverbs such as whom (the object form of "who"), whose (indicating possession), where (for places), and when (for times). Each of these allows you to add even more nuanced detail to your sentences. The table below previews how the introductory concepts you have studied relate to more advanced constructions.

Do not feel pressured to master all of these advanced forms immediately. The patterns you have practiced in this lesson—choosing between who, which, and that; placing the clause after the antecedent; and punctuating defining versus non-defining clauses—provide the structural foundation upon which all advanced relative clause work is built. Once these core patterns become automatic, the transition to structures involving whom, whose, and reduced forms will feel like natural extensions rather than entirely new concepts.