Complex Sentences
A complex sentence combines an independent clause with one or more dependent clauses. Understanding them is essential for expressing nuanced ideas in English.
What is a complex sentence?
A complex sentence contains one independent clause and at least one dependent clause. The dependent clause cannot stand alone — it relies on the main clause to make complete sense.
Subordinating conjunctions
The dependent clause is introduced by a subordinating conjunction. The conjunction signals the relationship between the two clauses.
| Relationship | Conjunctions | Example |
|---|---|---|
| Time | when, while, after, before, until, as soon as | Call me when you arrive. |
| Cause | because, since, as | She left because she was tired. |
| Condition | if, unless, provided that | I'll go if you come with me. |
| Contrast | although, even though, whereas | Although it was cold, he wore no coat. |
| Purpose | so that, in order that | She studied hard so that she could pass. |
Although the exam was difficult, most students passed.
He will help you if you ask him politely.
After the rain stopped, the children went outside to play.
She saved money so that she could travel abroad.
Clause order and punctuation
The dependent clause can come before or after the independent clause. When it comes first, use a comma to separate the clauses. When it comes second, no comma is needed.
| Order | Punctuation | Example |
|---|---|---|
| Dependent clause first | Comma required | Because she was tired, she went to bed. |
| Independent clause first | No comma needed | She went to bed because she was tired. |
Complex vs. compound sentences
| Type | Clauses | Conjunction type | Example |
|---|---|---|---|
| Compound | Two independent | Coordinating (FANBOYS) | She was tired, so she slept. |
| Complex | One independent + one dependent | Subordinating | She slept because she was tired. |
Types of dependent clauses
- Adverbial clauses — modify the verb, expressing time, cause, condition, or contrast: She smiled when she saw him.
- Relative clauses — describe a noun: The book that she recommended was excellent.
- Noun clauses — act as the subject or object: What he said surprised everyone.
Sentence fragment: Never use a dependent clause alone as a sentence — Because she was tired. is a fragment. It must be attached to an independent clause.
Tip: To check if a clause is dependent, try reading it alone. If it feels incomplete and leaves you asking "so what?", it is a dependent clause and needs a main clause to go with it.