Complex sentence
A complex sentence contains one independent clause and at least one dependent clause ('although the key was bent, the lock turned'), so the two halves are deliberately unequal in weight.
Although the key was bent, the lock turned. One clause stands on its own and one leans on it, and the leaning is the whole point: a complex sentence says this part matters more than that part.
How a complex sentence is built
It has one independent clause and at least one dependent clause. The dependent clause starts with a word that stops it standing alone:
- Subordinating conjunctions: because, although, though, when, while, if, unless, until, since, after, before, as, whereas, so that.
- Relative pronouns, which start a relative clause: who, whom, whose, which, that.
Complex sentence examples
The dependent clause is in italics.
- Because it was raining, the game was cancelled.
- We stayed inside until the storm passed.
- The girl who sat next to me moved away in March.
- If you see him, tell him I said sorry.
- She kept the letter, although she never read it again.
Complex vs compound
Compare the same two facts as a compound sentence: The key was bent, but the lock turned. Now they are equals, and the reader decides which one the scene is about. The complex version has already decided.
Order changes the effect
Put the dependent clause first and the reader waits for the main point, which builds a small pressure. That is the basic move of the periodic sentence. Put it last and the sentence lands its point and then qualifies it, the shape of a loose sentence: The lock turned, although the key was bent.
The punctuation follows the order. A dependent clause at the front takes a comma after it. At the end it usually takes none (We stayed inside until the storm passed), except before a clause of contrast such as although or whereas.
Why it matters in your writing
Complex sentences are what make prose feel thought about. A writer who only writes simple and compound sentences hands the reader an unsorted pile; a writer who writes nothing but complex sentences is sorting out loud, and the page slows to a crawl. The mix is the style. And a dependent clause on its own, with a full stop after it, is a fragment: Because it was raining. Attach it to a main clause, unless you are breaking the rule on purpose.
Frequently asked questions
What is a complex sentence?
A complex sentence has one main clause that could stand alone and at least one dependent clause that cannot, usually starting with a word like because, although, when or who. Example: 'When the bell rang, everyone ran.'
What is the difference between a compound and a complex sentence?
A compound sentence joins two main clauses as equals. A complex sentence joins a main clause to a dependent one, so one idea is ranked below the other.
Where does the comma go in a complex sentence?
If the dependent clause comes first, put a comma after it. If it comes after the main clause, you usually do not need one, except before words of contrast such as although, though and whereas.