A clause is a group of words that contains a subject and a verb. Clauses are the building blocks of sentences. Understanding how different clause types work — and how they connect — is essential for writing complex, accurate sentences at B1–B2 level and beyond.
Independent Clauses (Main Clauses)
An independent clause (also called a main clause) contains a subject and a verb and expresses a complete thought. It can stand alone as a sentence.
- She finished her essay. (complete sentence)
- The train was delayed. (complete sentence)
- He didn't answer. (negative)
Two independent clauses can be joined using a coordinating conjunction (for, and, nor, but, or, yet, so — FANBOYS): She finished her essay, and she submitted it on time. They can also be joined with a semicolon: The train was delayed; we missed our connection.
Dependent Clauses (Subordinate Clauses)
A dependent clause (subordinate clause) contains a subject and verb but cannot stand alone — it depends on an independent clause to complete its meaning. Dependent clauses are introduced by a subordinating conjunction.
- Although she was tired, she continued working. (the "although" clause cannot stand alone)
- Because it was raining, we cancelled the match.
- He left before she arrived.
Common subordinating conjunctions: because, although, even though, if, unless, when, while, before, after, since, as, until, so that, as long as, whereas, whether.
Relative Clauses (Adjective Clauses)
A relative clause modifies a noun or pronoun in the main clause, introduced by a relative pronoun: who, whom, whose, which, that.
Defining (restrictive) relative clauses identify which person or thing is meant. No commas. That or who/which can be used:
- The book that I borrowed was fascinating. (identifies which book)
- The woman who called left a message.
Non-defining (non-restrictive) relative clauses add extra information about a noun already identified. Commas are required. Only who/which/whose/whom are used (not that):
- My sister, who lives in Madrid, is visiting next week.
- The Eiffel Tower, which was built in 1889, attracts millions of visitors.
Adverbial Clauses
An adverbial clause modifies the main verb, answering questions like when, where, why, how, under what condition, or to what degree. It is a type of dependent clause introduced by a subordinating conjunction.
- Time: When the meeting ended, everyone left quickly.
- Reason: She stayed late because she had more work to finish.
- Condition: If you study regularly, your English will improve.
- Concession: Although the task was difficult, she completed it.
- Purpose: He spoke quietly so that nobody would hear.
- Result: It was so cold that the pipes froze.
- Contrast: Whereas he prefers cities, she loves the countryside.
Noun Clauses
A noun clause functions as a noun within a sentence — as subject, object, or complement. It is typically introduced by that, what, who, whether, if, how, where, when, why.
- As subject: What she said surprised everyone.
- As object: I know that she is right.
- After a preposition: He was interested in what they proposed.
- As complement: The question is whether we can afford it.
Practice Exercises
Grammar Quiz
Identify the clause type: independent, relative, adverbial, or noun clause.
Complete the Sentence
Choose the correct relative pronoun or subordinating conjunction.
Unjumble
Reorder words to form complex sentences with multiple clause types.
Cloze Dropdown
Select the right connector to join clauses correctly.
Practice What You've Learned
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Frequently Asked Questions
A clause contains both a subject and a verb: "she arrived" is a clause. A phrase is a group of words without both a subject and a verb: "in the morning," "the tall man," "quickly and efficiently" are all phrases. Phrases function as units within clauses (e.g., as noun, adjective, or adverb), but they cannot stand alone as sentences. The key test: does it have a subject-verb combination? If yes, it is a clause; if no, it is a phrase.
An independent clause (main clause) expresses a complete thought and can stand alone as a sentence: "The report was finished." A dependent clause (subordinate clause) has a subject and verb but cannot stand alone because it is introduced by a subordinating conjunction or relative pronoun: "Although the report was finished" — this leaves the reader waiting for more. Dependent clauses must be attached to an independent clause to form a complete sentence.
A defining (restrictive) relative clause identifies which person or thing is meant — without it, the sentence would be unclear or incomplete: "The man who called is my uncle." (Which man? The one who called.) No commas are used. A non-defining (non-restrictive) relative clause adds extra information about a noun already clearly identified — it can be removed without changing the core meaning: "My uncle, who called yesterday, is visiting next week." Commas are required. "That" cannot be used in non-defining clauses.
Who: refers to people as subject of the relative clause (The woman who phoned). Whom: refers to people as object of the relative clause (The manager whom I met). Which: refers to things (The book which I read / The film which won). That: refers to people or things in defining clauses only (The car that I bought / The teacher that helped me). Key: use who/which in non-defining clauses (with commas), never that. In informal speech, that often replaces who/which in defining clauses. Whom is formal; in informal English, who is widely used in object position.
An adverb is a single word that modifies a verb, adjective, or another adverb: "She left quickly." An adverbial clause is a dependent clause that functions as an adverb, giving information about time, reason, condition, concession, purpose, or result: "She left because she had a meeting." Both modify the verb, but the adverbial clause provides much richer, more specific information. Adverbial clauses are introduced by subordinating conjunctions and make writing more sophisticated and nuanced.
A noun clause is a dependent clause that functions as a noun — it can be the subject, object, or complement of a sentence. Test: can you replace it with "something" or "the fact"? If so, it is a noun clause. Examples: "I know that she is right" (object — I know something); "What she said surprised me" (subject — something surprised me); "The problem is whether we have enough time" (complement). Common introducers: that, what, whether, if, who, how, where, when, why.
The most frequent errors: (1) Using "that" in a non-defining clause: "My sister, that lives in Paris" — incorrect; use "who." (2) Missing commas in non-defining clauses: "My brother who is a doctor lives in London" — if you have only one brother, commas are required. (3) Double pronoun: "The man who I met him" — incorrect; remove "him" since "who" replaces it. (4) Wrong pronoun: "The book who I read" — incorrect; use "which" or "that" for things. (5) Omitting the relative pronoun when it is the subject: "The woman phoned me" vs. "The woman who phoned me" (the first is complete; the second is a relative clause fragment without a main clause).
A comma splice is the error of joining two independent clauses with only a comma: "She was tired, she went to bed early." This is grammatically incorrect. To fix it: use a coordinating conjunction (She was tired, so she went to bed early.); use a semicolon (She was tired; she went to bed early.); use a subordinating conjunction to make one clause dependent (Because she was tired, she went to bed early.); or make two separate sentences. Comma splices are common in learner writing and are penalised in Cambridge and IELTS examinations.
Using a variety of clause types demonstrates grammatical range, which is a key assessment criterion in both IELTS (Grammatical Range and Accuracy) and Cambridge exams. Complex sentences with adverbial clauses show logical reasoning: "Although urban areas offer more opportunities, rural communities provide a stronger sense of belonging." Relative clauses add precision: "The policy, which was introduced in 2020, has had mixed results." Noun clauses allow hedging: "It is widely believed that economic growth depends on education." Aiming for a mix of simple, compound, and complex sentences is the most effective strategy.
All three introduce concessive adverbial clauses (meaning "despite the fact that") and are largely interchangeable. "Although" is the most neutral and common in both formal and informal writing. "Even though" adds extra emphasis, stressing that the contrast is surprising or strong: "Even though she had never played before, she won." "Though" is more informal and can also be used as an adverb at the end of a sentence: "It was expensive. It was worth it, though." In formal academic writing, "although" and "even though" are preferred over "though."