How to write complex sentences with because, when, if
Short answer: A complex sentence has a main idea and an extra idea that starts with because, when or if. Because tells why, when tells when, and if tells what happens when something is true. If the extra idea comes first, put a comma after it: Because it was raining, we stayed home.
🎯 I can join ideas with because, when, if.
At a glance
| Word | Tells | Rewrite example |
|---|---|---|
| because | why | We stayed home. It was raining. → We stayed home because it was raining. |
| when | when | I eat. I am hungry. → I eat when I am hungry. |
| if | what happens if | You study. You will pass. → If you study, you will pass. |
How to write it
- Write your main idea.
- Decide what the extra idea tells: a reason, a time or a condition.
- Add because, when or if before the extra idea.
- If the extra idea comes first, add a comma after it.
Rewrite practice
- Before:
I took an umbrella. It was raining.
After: I took an umbrella because it was raining.
because gives the reason. - Before:
I call my mom. I get home.
After: I call my mom when I get home.
when gives the time. - Before:
It rains. We will stay inside.
After: If it rains, we will stay inside.
if gives the condition; the comma follows the if part.
Common mistakes
If it will rain, we stay inside.→ If it rains, we will stay inside.
After if, use the present; will goes in the main part.Because it was late. We went home.→ Because it was late, we went home.
A because part alone is not a sentence; join it to the main idea.When I was five, so I started school.→ When I was five, I started school.
No so after a when part.
Because and so
Because and so tell the same idea from opposite sides.
| Word | Pattern | Example |
|---|---|---|
| because | result because reason | We stayed in because it rained. |
| so | reason, so result | It rained, so we stayed in. |
Check yourself
- Which word gives a reason?
Show the answer
because It answers why.
- Where does the comma go in “If it rains we will stay in”?
Show the answer
After rains. A comma follows the if part.
- Fix: “If it will rain, we stay.”
Show the answer
If it rains, we will stay. Present after if.
Rule cards that help
- Joining words: and, but, or, so: and, but, or and so join two ideas of the same kind.
- because: giving reasons: because gives the reason. It answers the question Why?
- Future: will and won't: will talks about the future. After will, use the plain action word.
- when and if: when tells the time. if tells what must happen first. After if, use the present for the future.
Sounds that help
- Rhythm & Chunking: Pause after the because / when / if part
Questions
What is a complex sentence?
A sentence with a main idea and an extra idea that cannot stand alone, such as because it was raining.
When do I use a comma?
Use a comma when the extra idea comes first. When it comes second, no comma is needed.
Where can I read the rule?
The rule articles for because, and when and if, explain these words in detail.
Part of 🌉 Because, when, if, who and more (stone 2 of the Learning Path). See also the English writing guide. Đọc bằng tiếng Việt.
Written for English learners by the English for Fun team. How we write our lessons · Last updated 2026-11-05.
Reviewed by Chinh Q. Hoang, PhD, founder, English for Fun · 2026-10-30