Grammar
Compound sentences: join ideas clearly
Your message can say two useful things at once: The train was late, so I called the office. Each part is complete, and so shows the result.
Join two related independent clauses in a compound sentence by choosing a coordinating conjunction that matches the relationship between the ideas.
Read and practice
Read the examples and try the written questions in this guide. Listening recordings are not available for this lesson yet.
Try the written questions
The train was late, so I called the office. /ðə treɪn wəz leɪt səʊ aɪ kɔːld ði ˈɒfɪs/
The short answer
A compound sentence joins two complete clauses with a coordinating conjunction. Choose and to add an idea, but for a contrast, or for a choice, and so for a result. When these words join two complete clauses, use a comma before the conjunction.
I wanted to walk, but the rain became heavy.
Why it works: I wanted to walk and the rain became heavy are complete clauses. But shows that the second idea contrasts with the plan.
5 more examples
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The cafe was full, so we sat outside.
The cafe being full led to the decision to sit outside.
Not this:The cafe was full,
butwe sat outside. What changes: But can show a contrast, but it does not state the cause-and-result connection as clearly as so. -
Lina finished the report, and she sent it before lunch.
The second complete clause adds the next action.
Not this:Lina
finished the report and sent itbefore lunch. What changes: This is a clear sentence, but it has one subject, Lina, with two verbs. It is not a compound sentence. -
I called twice, but nobody answered.
Nobody answering contrasts with the expected result of calling twice.
Not this:I called twice,
so nobody answered. What changes: So gives the wrong relationship because calling twice does not cause nobody to answer. -
You can save the file now, or you can finish it tomorrow.
The clauses give two possible choices.
Not this:You can save the file now,
andyou can finish it tomorrow. What changes: And adds information, while or is clearer when the sentence asks the reader to choose one option. -
The map was old, yet it was still useful.
Yet works like but here and introduces an unexpected contrast.
Not this:The map was old,
soit was still useful. What changes: So would make age the reason that the map remained useful, which is not the intended meaning.
Read the full guide
First, test each part on its own. The lights went out is a complete clause. We used our phones is also a complete clause. Put them together with a conjunction that gives the intended meaning: The lights went out, so we used our phones.
Check that each idea is complete
A compound sentence needs two independent clauses. Each clause can be a sentence on its own. Read the first part, then the second part. If either part leaves the reader waiting for the rest of the idea, it is not an independent clause.
The meeting ended, and everyone packed their notes.
The meeting ended is complete. Everyone packed their notes is also complete.
Can 'because the meeting ended' stand alone as a complete sentence in this use?
No. Because the meeting ended gives a reason, but it needs a main clause to complete the thought.
Use and to add another idea
Use and when the second clause adds information, another event, or another fact. The ideas may happen in sequence, but and does not need to explain a strong contrast or a result. Make sure both sides still have their own subject and verb.
The store opened at eight, and the first customers arrived soon after.
The second clause adds the next event after the store opened.
Which conjunction adds an idea: 'The class ended, ___ we put the chairs away'?
Use and when you simply add the next action: The class ended, and we put the chairs away.
Use but for a contrast
Use but when the second clause changes what the reader may expect from the first clause. The two statements can both be true. But signals that the second idea limits, corrects, or contrasts with the first one.
The route was shorter, but it was much steeper.
A shorter route may sound easier. But introduces the contrasting detail that it was steeper.
Choose the clearer link: 'The room was small, ___ it felt comfortable.'
Use but. The second clause contrasts with the possible expectation that a small room will not feel comfortable.
Use or and so for choice or result
Use or when the clauses offer alternatives. Use so when the second clause is a result of the first clause. These words do more than join the clauses. They tell the reader whether to choose between possibilities or follow a cause and result.
We can leave now, or we can wait for the next bus.
Or presents two possible actions.
The road was blocked, so the driver chose another route.
So shows that choosing another route happened because the road was blocked.
Make the comma serve the structure
Use a comma before a coordinating conjunction when it joins two independent clauses. Do not use that comma just because you see and or but. A comma is not needed when the conjunction joins words, phrases, or two verbs with the same subject.
Nina wrote the email, and Omar checked the address.
There is a comma because Nina wrote the email and Omar checked the address are complete clauses.
Does 'Nina wrote the email and checked the address' need a comma before and?
No. Nina is the subject of both wrote and checked, so the sentence has one independent clause with two verbs.
Before you go
Remember this
Find the subject and verb in each part. If each part can stand alone, you can make a compound sentence with a coordinating conjunction. Choose the conjunction from the meaning, and use a comma before it when it joins two complete clauses.
Practice with the written examples
You can practice with the written questions in the Learn tab. Each answer includes an explanation.
Try the written questionsListening test not available yet
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Try the written questionsQuestions about "Compound sentences: join ideas clearly"
What is a compound sentence?
A compound sentence joins two or more independent clauses. Each clause has its own subject and verb and can stand alone as a sentence. A coordinating conjunction such as and, but, or, so, or yet shows how the ideas relate.
The cafe was full, so we sat outside.
Which conjunction should I use in a compound sentence?
Choose the conjunction from the relationship you mean. Use and to add an idea, but or yet for contrast, or for a choice, and so for a result. Read the two clauses separately before you choose the linking word.
The cafe was full, but we sat outside.
Do I need a comma before and in a compound sentence?
Use a comma before and, but, or, so, or yet when the conjunction joins two independent clauses. Do not add the comma when the word joins only two nouns, two phrases, or two verbs with the same subject.
Lina finished the report, and she sent it before lunch.
Is a sentence with and always a compound sentence?
No. And can join words, phrases, or verbs as well as clauses. In 'Rina packed a bag and checked her ticket,' one subject does both actions. Check whether both sides of and have a complete clause before calling the sentence compound.
Lina finished the report and sent it before lunch.
What is the difference between a compound and a complex sentence?
A compound sentence joins independent clauses of equal grammatical importance. A complex sentence has a main clause and a subordinate clause that cannot stand alone. Words such as because, if, and although commonly introduce a subordinate clause.
I called twice, but nobody answered.