A complex sentence contains one independent clause and at least one dependent clause. In When the bell rang, the students left, the students left can stand alone, but when the bell rang cannot, so the sentence is complex. Other examples: I'll call you if I'm late. The jacket that I bought was on sale. She said that she was tired.
Complex sentences sit alongside three other types: simple (one independent clause), compound (two or more independent clauses), and compound-complex (two or more independent clauses plus at least one dependent clause). The 30 exercises below cover identifying each type, the comma rule when the dependent clause comes first, and combining short sentences into complex ones.
Complex Sentences Quiz: 30 Questions
Warm-up · name the sentence type
Core · commas and combining
Challenge · harder types and revisions
Answer key and explanationsOpen after you finish the quiz.
- 1. SimpleThere is one subject (the dog) and one finite verb (barked), so there is one independent clause and no dependent clause. One independent clause on its own makes a simple sentence.
- 2. CompoundI studied and I failed the test are both independent clauses, joined by the coordinating conjunction but. Two independent clauses and no dependent clause make a compound sentence.
- 3. ComplexAlthough makes I studied a dependent clause, and I failed the test is the independent clause. One independent clause plus one dependent clause is a complex sentence.
- 4. Compound-complexThere are two independent clauses (I failed the test; I had to retake it) joined by and, plus one dependent clause (although I studied). That combination is compound-complex.
- 5. SimpleOne subject (she) has two verbs (sings and plays), which is a compound predicate, not two clauses. With only one subject-verb unit, this is a simple sentence.
- 6. ComplexIf you heat ice is a dependent clause of condition, and it melts is the independent clause. Conditional sentences with if are complex sentences.
- 7. CompoundBoth halves (we can leave now; we can wait for Sam) are independent clauses, joined by a comma and the coordinating conjunction or. That makes it compound.
- 8. I like tea because it calms me.Because it calms me is a dependent clause attached to the independent clause I like tea. The and and semicolon versions join two independent clauses (compound), and I like tea and coffee is simple.
- 9. The phone rang, and I answered it.The phone rang, and I answered it joins two independent clauses, so it is compound. The others each contain a dependent clause: an adverb clause (while…), a noun clause (whoever wins), and a relative clause (that you baked).
- 10. one independent clause and at least one dependent clauseThat is the definition: one independent clause plus one or more dependent clauses. Two independent clauses would make it compound, and complex sentences do not need a semicolon or any minimum length.
- 11. Before you leave, please lock the door.When the dependent clause comes first, put a comma after it, before the main clause. Writers sometimes skip it after a very short opener, but the comma is the standard choice. A semicolon cannot separate a dependent clause from its main clause.
- 12. Please lock the door before you leave.When a time, cause, or condition clause follows the main clause, it normally takes no comma. The comma before the main clause applies only when the dependent clause comes first.
- 13. I enjoyed the film, although it was too long.Contrast clauses introduced by although, though, or whereas are often set off with a comma even at the end of the sentence. The full-stop version leaves a fragment, and the other two put commas in places that split the clauses apart.
- 14. Because the museum was closed, we went to the park.Because turns the first sentence into a dependent clause, which makes the result complex. The and version is correct but compound; the first is a comma splice, and the last misplaces the comma after so.
- 15. AlthoughAnyway signals that the result is unexpected, so the clause must show contrast: although. Because and since give a reason, which clashes with anyway, and so that expresses purpose.
- 16. A fragment: the dependent clause has no main clauseWhenever makes the clause dependent, and nothing completes it. Add an independent clause to make it complex: Whenever I visit my grandmother, she bakes bread.
- 17. everyone went back to workEveryone went back to work has its own subject and verb and can stand alone. The meeting ended sits inside the dependent clause introduced by when, and went back to work has no subject.
- 18. The student who won the prize is my cousin.Who won the prize is a relative clause describing student, inside the independent clause the student is my cousin. The second option is compound, and a student in the third is an appositive phrase, not a clause.
- 19. I got home I made dinner.I got home and I made dinner are two independent clauses with no punctuation or conjunction between them, so they are fused. Making one clause dependent (When I got home, …) is one fix.
- 20. Noun clauseWhere he lives is the object of know (I don't know his address). It fills a noun slot, so it is a noun clause; it would be a relative clause only if it described a noun, as in the house where he lives.
- 21. Compound-complexThere are two independent clauses (the report was excellent; nobody read it) joined by but, plus a dependent relative clause (that she wrote). Two independent clauses with at least one dependent clause make a compound-complex sentence.
- 22. SimpleStudying late at night is a participial phrase: it has no subject and no finite verb. The only clause is she finally understood the problem, so the sentence is simple despite its length.
- 23. ComplexThat he would call is a noun clause acting as the object of said, and he said is the independent clause. Reported speech with that is a common kind of complex sentence.
- 24. My brother, who lives in Toronto, is visiting next week.With only one brother, who lives in Toronto is extra information, so it is a non-defining clause and takes a pair of commas: one before who and one after Toronto. Leaving out either comma breaks the pair.
- 25. Since you're busy, I'll call later.Since you're busy means because you're busy, so it gives a reason. In the other sentences since points to a starting time, either as a preposition (since 2019, since school) or as a time conjunction (since the baby arrived).
- 26. I was late because my car wouldn't start.The car is the reason for the lateness, so because must introduce my car wouldn't start. The second option reverses cause and effect, the first is a comma splice, and the third surrounds because with commas for no reason.
- 27. Unless you hurry, you'll miss the train.Unless means if not, so unless you hurry equals if you don't hurry. Until marks a time limit, although concedes a fact, and whereas contrasts two facts, so none of them gives the same meaning.
- 28. ThreeThere are three: when I arrived (adverb clause), who runs the café (relative clause), and that the kitchen was closed (noun clause). The independent clause is the woman told me.
- 29. Because it rained, the match was cancelled, and the fans went home.The third option has two independent clauses (the match was cancelled; the fans went home) plus a dependent clause (because it rained). The others are complex, compound, and simple in that order.
- 30. A comma (,)As soon as the results came in is a dependent clause at the start of the sentence, so it is followed by a comma. A full stop would leave it as a fragment, and a semicolon cannot join a dependent clause to a main clause.
What Is a Complex Sentence?
A complex sentence has exactly one independent clause and one or more dependent clauses. The independent clause carries the main statement; the dependent clause adds background such as time, reason, condition, or contrast, or describes a noun, or acts as a subject or object.
The dependent clause can come first, last, or in the middle: Because it was late, we took a taxi. / We took a taxi because it was late. / The taxi that we took was expensive.
- Adverb clause: I'll wait here until you come back.
- Adverb clause first: If you need help, just ask.
- Relative clause: The book that I'm reading is about Rome.
- Noun clause: Nobody knows why the lights went out.
- Two dependent clauses: When I got home, I found the parcel that you sent.
Length does not make a sentence complex. A long sentence full of phrases can be simple, and a five-word sentence can be complex (I left when she arrived).
Simple vs Compound vs Complex vs Compound-Complex
Sentence types are defined by their clauses. Count the independent clauses and check whether there is at least one dependent clause.
- Simple: one independent clause. The bus was late.
- Compound: two or more independent clauses. The bus was late, so I walked.
- Complex: one independent clause and one or more dependent clauses. Because the bus was late, I walked.
- Compound-complex: two or more independent clauses and one or more dependent clauses. Because the bus was late, I walked, and I still arrived on time.
- Compound clauses are joined by for, and, nor, but, or, yet, so, or a semicolon. Dependent clauses start with subordinating conjunctions or relative words.
The Comma Rule for Complex Sentences
When the dependent clause comes first, put a comma after it: When the film ended, we went home. When the main clause comes first, you usually need no comma: We went home when the film ended.
Two exceptions are worth knowing. Contrast clauses (although, though, even though, whereas) are often preceded by a comma even at the end, because they add a qualification: I like the job, although the hours are long. Non-defining relative clauses always take commas wherever they appear: My car, which is ten years old, still runs well.
- Dependent first: If it rains, we'll stay home.
- Dependent last: We'll stay home if it rains.
- Contrast clause last: She passed, although she barely studied.
- Non-defining relative clause: Our manager, who joined in May, is great.
- Never: a semicolon between a dependent clause and its main clause.
Some writers drop the comma after a very short introductory clause (When I left I locked up). The comma is still the safe, standard choice in formal writing.
How to Build a Complex Sentence
Start with two related simple sentences. Decide which idea matters more and keep it as the independent clause. Then put a subordinating conjunction that shows the relationship in front of the other one.
- Time: The guests arrived. We served dinner. → After the guests arrived, we served dinner.
- Cause: The road was icy. The school closed. → The school closed because the road was icy.
- Condition: You finish early. You can leave. → If you finish early, you can leave.
- Contrast: The flat is small. It's comfortable. → Although the flat is small, it's comfortable.
- Relative: I met a woman. She speaks five languages. → I met a woman who speaks five languages.
Use only one linking word per link. Although it was cold, but we swam uses two connectors and is wrong; choose although or but.
Keep practicing
Frequently Asked Questions
What is an example of a complex sentence?
Although it was raining, we went for a walk. Here we went for a walk is the independent clause and although it was raining is the dependent clause. Other examples: I'll call you when I land. The man who fixed my bike was very kind.
What is the difference between a compound and a complex sentence?
A compound sentence joins two or more independent clauses, usually with and, but, or so (It rained, so we stayed in). A complex sentence has one independent clause plus at least one dependent clause, usually introduced by a word like because, when, or who (We stayed in because it rained).
Do complex sentences always need a comma?
No. You normally need a comma when the dependent clause comes before the main clause (If you're ready, let's go). When the main clause comes first, you usually do not (Let's go if you're ready), except before contrast words like although and with non-defining relative clauses.
Check the Commas in Your Complex Sentences
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