Full stops and commas: where one idea ends
Short answer: A full stop ends a complete idea. A comma goes after a starting part, such as When I got home, or If it rains,. A comma alone cannot join two complete sentences: use a full stop, or add a joining word such as and or but. Do not pile many ideas into one very long sentence.
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At a glance
| Mark | Use | Example |
|---|---|---|
| full stop | ends a complete idea | The bell rang. We went inside. |
| comma after a starting part | when, if, before, after... | If it rains, we will stay home. |
| comma + joining word | joins two sentences | I like apples, and my brother likes bananas. |
| comma in a list | between items | I have a cat, a dog and a bird. |
In short
- A full stop ends a complete idea.
- A comma goes after a starting when / if / before part.
- A comma alone cannot join two sentences.
What is the rule for “Full stops and commas between ideas”?
The rule
A full stop ends a complete idea. A comma goes after a starting part.
How it looks
When …, main idea. · Idea one. Idea two. · Idea one, and idea two.
What it means
They show where one idea ends and the next begins.
When to use it
Check your writing before you finish.
How it works
- Check each sentence: does it have a subject and a verb and make sense alone? Then end it with a full stop.
- If a sentence starts with when, if, before, after or although, put a comma after that part.
- To join two sentences, use a joining word with a comma, or use two sentences.
- Read the writing aloud. Where you pause, check if you need a comma or a full stop.
Examples of “Full stops and commas between ideas”
- If it rains, we will stay home.
A comma after the if part. - The bell rang. We went inside.
Two sentences: a full stop between them. - I like apples, and my brother likes bananas.
A comma and a joining word. - When I got home, I ate and I read.
Do not make one very long sentence. - When we arrived, the show had started.
A comma after the starting part. - I was tired, so I went to bed.
A comma before so, which joins two sentences. - My bag is blue, my shoes are red, and my hat is green.
A list of three ideas. - It was late. We went home.
Two short sentences, each with a full stop.
Common mistakes with “Full stops and commas between ideas”
I like apples, my brother likes bananas.→ I like apples. My brother likes bananas.
A comma alone cannot join two sentences.When I got home I ate lunch.→ When I got home, I ate lunch.
A comma after the starting part.When I got home I ate lunch and I watched TV and I slept.→ When I got home, I ate lunch. Then I watched TV and slept.
Too many ideas in one sentence.I like tea but, I don’t like coffee.→ I like tea, but I don’t like coffee.
The comma goes before but, not after it.Mia has a cat a dog and a rabbit.→ Mia has a cat, a dog and a rabbit.
Use commas in a list.
Exceptions: watch out
- Run-on sentences
If you use and again and again, make two sentences instead: When I got home, I ate lunch. Then I watched TV.
Comma, full stop or semicolon?
At this level, use a full stop to end an idea and a comma with a joining word or after a starting part. The semicolon can wait.
| Mark | When | Example |
|---|---|---|
| full stop (.) | idea is complete | It rained. |
| comma (,) | after a starting part or before and / but / so | If it rains, we stay. |
| comma only | never join two sentences | not: It rained, we stayed. |
See also: Joining words: and, but, or, so
Check yourself
- Fix: “I like apples, my brother likes bananas.”
Show the answer
I like apples. My brother likes bananas. A comma alone cannot join two sentences.
- Add a comma: “When I got home I ate lunch.”
Show the answer
When I got home, I ate lunch. Comma after the starting part.
- Fix: “Mia has a cat a dog and a rabbit.”
Show the answer
Mia has a cat, a dog and a rabbit. Commas in a list.
How to practice “Full stops and commas between ideas”
The interactive version adds step-by-step help, spoken instructions and a quick check. One rule card, one sound lesson and the first lesson of every stone are free to try; the rest is part of Full Access. See Full Access.
- Practice lesson: Full stops and commas between ideas
Questions
What is a comma splice?
A comma splice joins two complete sentences with only a comma: It was late, we left. Fix it with a full stop or a joining word.
Do I put a comma before “and”?
Between two sentences, yes: I like tea, and she likes coffee. In a short list of three, you can leave it out.
How long should a sentence be?
Short enough to follow. If you use and three times, consider two sentences.
More Linking Ideas Further rules
- before and after: before and after put two events in time order. Each part needs its own subject and verb.
- Past continuous: was / were + -ing: was or were + -ing tells what was happening at a time in the past.
- when and while in stories: while goes with the longer action (was / were + -ing). when goes with the short action that interrupts.
- Why we do things: to and so that: To give a reason for an action, use to + the plain action word. so that can be followed by a full idea.
- Describing people with who: who adds information about a person. It takes the place of he or she, so do not say it twice.
- Describing things with that and which: that and which add information about a thing. Do not say the thing twice.
Used in these writing topics
Part of the 📘 Grammar tool. Level G5: Linking Ideas Further. 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
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