Complex Sentences
A complex sentence is a sentence that has two parts: a main clause (the main idea) and a subordinate clause (an extra idea that depends on the main clause). Together, they make your writing more interesting and detailed.
What You'll Learn
- What a main clause and a subordinate clause are
- How to join a main clause and a subordinate clause using subordinating conjunctions
- How to place the subordinate clause before or after the main clause
- How to use correct punctuation in complex sentences
When to Use
- To give a reason: "I brought my umbrella because it was raining."
- To show when something happened: "When the bell rang, the pupils lined up."
- To set a condition: "You can go out to play if you finish your homework."
- To add contrast: "Although she was tired, she kept practising her piano."
- To explain purpose: "He studied hard so that he could pass the test."
How to Form
Parts of a Complex Sentence
| Part | What it does | Example |
|---|---|---|
| Main clause | Can stand alone as a sentence | I stayed indoors. |
| Subordinate clause | Cannot stand alone; needs the main clause | because it was raining |
| Complex sentence | Main clause + subordinate clause joined together | I stayed indoors because it was raining. |
Subordinating Conjunctions
These are the joining words that start a subordinate clause.
| Type | Conjunctions | Example |
|---|---|---|
| Time | when, while, before, after, until | After the movie ended, we went home. |
| Reason | because, since, as | She smiled because she won the prize. |
| Condition | if, unless | If it rains, we will cancel the picnic. |
| Contrast | although, even though | Although he ran fast, he did not win. |
| Purpose | so that, in order to | She saved her money so that she could buy a book. |
Two Ways to Arrange a Complex Sentence
| Order | Structure | Punctuation | Example |
|---|---|---|---|
| Main clause first | Main clause + subordinate clause | No comma needed | I will wait until you are ready. |
| Subordinate clause first | Subordinate clause + main clause | Comma after subordinate clause | Until you are ready**,** I will wait. |
Key Rules
- A main clause can stand alone: It makes sense on its own. "The children played in the park." is a complete sentence.
- A subordinate clause cannot stand alone: "Because it was sunny" is not a complete sentence. It needs a main clause to complete the meaning.
- Use a subordinating conjunction to join them: Words like because, when, if, although, before, after, and until connect the subordinate clause to the main clause.
- Comma rule -- subordinate clause first: When the subordinate clause comes before the main clause, put a comma after it. "When the rain stopped**,** we went outside."
- No comma -- main clause first: When the main clause comes first, you usually do not need a comma. "We went outside when the rain stopped."
- Do not confuse with compound sentences: A compound sentence joins two main clauses with and, but, or, so. A complex sentence joins a main clause with a subordinate clause using a subordinating conjunction.
Common Mistakes
| Wrong | Right | Why |
|---|---|---|
| Because I was hungry. I ate my lunch. | Because I was hungry, I ate my lunch. | The subordinate clause cannot be a separate sentence |
| I stayed home, because I was sick. | I stayed home because I was sick. | No comma when the main clause comes first |
| When the bus came we got on it. | When the bus came, we got on it. | Comma needed when the subordinate clause comes first |
| Although she studied hard but she failed. | Although she studied hard, she failed. | Do not use although and but together; pick one |
| If you are free, and you can help me. | If you are free, you can help me. | The subordinate clause already links the two ideas; no extra conjunction needed |
Clue Words
Time clues
when, while, before, after, until, as soon as
Reason clues
because, since, as
Condition clues
if, unless
Contrast clues
although, even though, though
Purpose clues
so that, in order to
Tip: If you see one of these clue words at the start of a clause, that clause is a subordinate clause. It needs a main clause to make a complete sentence.
Practice Tips
- The "stand-alone" test: Cover one part of the sentence. Can it make sense by itself? If yes, it is the main clause. If no, it is the subordinate clause.
- Spot the conjunction: Circle the subordinating conjunction. Everything on its side is the subordinate clause. Everything on the other side is the main clause.
- Flip the sentence: Try moving the subordinate clause to the front or back. Both orders should make sense. Remember to add or remove the comma.
- Read aloud: Read the sentence out loud. If you hear a natural pause after a subordinate clause at the front, that is where the comma goes.
Quick Reference
| I want to... | Conjunction | Example |
|---|---|---|
| Give a reason | because, since | I wore a jacket because it was cold. |
| Show timing | when, before, after, until | Before you leave, pack your bag. |
| Set a condition | if, unless | We will go if the weather is fine. |
| Show contrast | although, even though | Although it was late, she kept reading. |
| Explain a purpose | so that | He practised daily so that he could improve. |
| Clause Order | Comma? | Example |
|---|---|---|
| Main clause first | No | She laughed because the joke was funny. |
| Subordinate clause first | Yes | Because the joke was funny, she laughed. |