To combine short sentences, choose a link that shows how the ideas relate, then punctuate it correctly. The two common errors are leaving the sentences choppy and joining them with only a comma.
This skill appears in writing tasks and in any rewriting task in sentence building and paraphrase.
How do you decide how to join two sentences?
First ask what the relationship is between the ideas. Is one the reason for the other, a contrast, a sequence, or just an addition? The relationship picks the linking word.
| Relationship | Linking word | Example |
|---|---|---|
| addition | and | The room was quiet, and the lights were dim. |
| contrast | but, although | The exam was long, but it was fair. |
| reason | because, since | We stayed in because it rained. |
| result | so | It rained, so we stayed in. |
| sequence | after, before, when | After the bell rang, we left. |
Then punctuate. With and, but, so between two full clauses, put a comma before the word. When the sentence starts with although, because or after, put a comma after the first clause.
Worked example
Combine these three sentences into one:
The bus was late. The students waited outside. It started to rain.
Step 1, find the relationships. The bus being late is the reason the students waited. The rain is an extra event that happened during the wait.
Step 2, choose the main idea. The main idea is that the students waited. The late bus is background, so it can become a short opening clause.
Step 3, join. Because the bus was late, the students waited outside until it started to rain.
Step 4, check. Are all three facts still there? Late bus, waiting outside, rain: yes. Is there a comma after the opening clause? Yes. Does it have one main clause? Yes.
An alternative is The bus was late, so the students waited outside, and then it started to rain. Both are correct. Choose the one that keeps the stress where you want it.
The mistake to watch for
Mistaken answer: The bus was late, the students waited outside.
Two complete sentences are joined by a comma only. This is a comma splice.
There are four repairs: add and or so after the comma, change the comma to a semicolon, change it to a full stop, or turn one clause into an opening because clause. A quick test is to cover everything before the comma. If what remains can stand alone as a sentence, you need more than a comma.
Check yourself
1. Combine with a linking word that shows result: The road was flooded. We took another route.
Show answer
The road was flooded, so we took another route. The second event is the result of the first, so so fits, with a comma before it.
2. Correct the run-on: I like the park, it is quiet in the morning.
Show answer
I like the park because it is quiet in the morning. When the second clause is the reason, because works with no comma. A semicolon or full stop would also fix it, but would not show the reason.
3. Combine into one sentence: Rina packed her bag. She checked the timetable. She left for school.
Show answer
After Rina packed her bag and checked the timetable, she left for school. The first two actions share a subject and are joined by and. The sequence word after shows that leaving came last.
Where this leads next
Once joins feel natural, look at how to replace a repeated noun with clear reference, because joined sentences often repeat the same word. Then test yourself with the mixed sentence practice set, and try the summary selection and paraphrase studio.
Some students can explain the rule but still write comma splices when they write quickly. A teacher who reads your own writing can spot that habit early, and that is part of our online one-to-one English as a Second Language tuition.