Grammar
Complex sentences: clauses and logical links
The office was quiet because everyone had gone home. The first part gives the main message. The second part explains the reason.
Build complex sentences with a main clause and a subordinate clause to show reason, time, condition, or contrast.
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
I'll send the file when I finish the report. /aɪl send ðə faɪl wen aɪ ˈfɪnɪʃ ðə rɪˈpɔːt/
The short answer
Start with a complete main clause, then add a subordinate clause when you need to show how two ideas connect. Use because for a reason, when for a time, if for a condition, and although for a contrast. If the subordinate clause comes first, put a comma before the main clause.
Although the bus was crowded, Maya found a seat.
Why it works: Although introduces the contrast. The comma separates the opening subordinate clause from the main clause.
5 more examples
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We took a taxi because the last bus had left.
Because introduces the reason for taking a taxi.
Not this:We took a taxi,
andthe last bus had left. What changes: And joins two main clauses, but it does not state the reason as clearly as because. -
When the library opens, I will return the books.
The opening clause tells the reader when the return will happen.
Not this:
The library opensat nine. What changes: This is a main clause because it can stand alone as a complete message. -
If you need help, call the reception desk.
If introduces the condition for making the call.
Not this:
You need help. What changes: This main clause is complete, but it does not give the instruction that follows from the condition. -
Although the instructions looked simple, we checked them twice.
Although shows a contrast between the simple-looking instructions and the careful check.
Not this:The instructions looked simple,
sowe checked them twice. What changes: So suggests a result, which changes the intended contrast. -
I will wait until the technician arrives.
Until gives the time limit for waiting.
Not this:
The technician arrivesat noon. What changes: This main clause states a time of arrival without connecting it to another action.
Read the full guide
A long sentence is not automatically a complex sentence. Look for a clause, which has a verb and usually a subject. In I stayed at home because I felt unwell, I stayed at home is a complete main clause. Because I felt unwell gives a reason, so it depends on the main clause. The joining word tells the reader how to understand the second idea.
Find the main clause first
A main clause can stand alone as a complete sentence. It has a verb and gives a full message. Find this clause first, then look for any extra clause that depends on it.
The meeting starts at ten.
The meeting starts at ten is a main clause because it makes sense by itself.
Because the meeting starts at ten.
Because the meeting starts at ten leaves the reader waiting for the result or main message.
Which words can stand alone as a complete sentence: 'The meeting starts at ten' or 'Because the meeting starts at ten'?
The meeting starts at ten can stand alone. It is the main clause.
Use because to give a reason
Use because when one clause explains why the action or situation in the main clause happened. The clause after because is subordinate because it supplies the reason.
I wore a jacket because the evening was cold.
Because the evening was cold explains why the speaker wore a jacket.
Because the evening was cold, I wore a jacket.
The same reason comes first here, so a comma separates it from the main clause.
Choose the word that gives a reason: 'I left early ___ I felt sick.'
Use because: I left early because I felt sick.
Use time clauses for order and timing
Use when, before, after, or until to connect an action to a time. These words help the reader understand the order of events or the point when something changes.
Please turn off the lights before you leave.
Before you leave tells the reader when to turn off the lights.
After the class ended, we asked the teacher a question.
After the class ended comes first, so it is followed by a comma before the main clause.
Which word shows that one action happens after another: 'I will call you ___ I arrive'?
Use when or after, depending on the exact meaning. I will call you when I arrive is a common choice.
Use if to state a condition
Use if when the main clause depends on a possible situation. The if clause gives the condition. The main clause gives what will happen, what someone should do, or what is true in that condition.
If the printer stops again, tell the office manager.
If the printer stops again is the condition. Tell the office manager gives the action to take.
We can sit outside if the rain stops.
The main idea comes first, and if the rain stops adds the condition.
Complete the sentence: 'If you see Daniel, ___ him my message.'
Use a main clause such as tell him my message. The if clause needs a result or instruction.
Use although to show a contrast
Use although when one fact makes another fact surprising or unexpected. The two clauses are both true, but the subordinate clause gives background that contrasts with the main clause.
Although the café was busy, we found a quiet table.
The busy café could make a quiet table seem unlikely, so although marks the contrast.
The team won although two players were absent.
Although two players were absent follows the main clause and explains the surprising part of the result.
Which word shows contrast: '___ it was raining, the match continued'?
Use although: Although it was raining, the match continued.
Place the comma where it helps
When a subordinate clause comes before the main clause, use a comma after it. When the main clause comes first, a comma is usually unnecessary before because, when, if, or although. The punctuation helps the reader see the structure.
When the alarm rang, I got up.
The opening time clause ends before the comma, and the main clause follows.
I got up when the alarm rang.
The main clause comes first, so this sentence does not usually need a comma before when.
Where does the comma go: 'If the key does not work call the building manager'?
Write: If the key does not work, call the building manager. The opening if clause is followed by a comma.
Before you go
Remember this
A complex sentence joins a main clause to a subordinate clause. Choose a joining word that matches the relationship between the ideas. Use because for a reason, when or until for time, if for a condition, and although for contrast. Use a comma after a subordinate clause that comes first.
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
This lesson does not have the recordings needed for a listening test. Use the written questions in the guide to check your understanding.
Try the written questionsQuestions about "Complex sentences: clauses and logical links"
What is a complex sentence in English?
A complex sentence has one main clause and at least one subordinate clause. The main clause can stand alone, while the subordinate clause adds a relationship such as reason, time, condition, or contrast. In 'I wore a jacket because the evening was cold,' the first clause is complete and the because clause explains why.
We took a taxi because the last bus had left.
What is the difference between a main clause and a subordinate clause?
A main clause gives a complete message by itself, such as 'The meeting starts at ten.' A subordinate clause depends on a main clause, such as 'because the meeting starts at ten.' The joining word makes the second clause dependent and shows how its information connects to the main idea.
We took a taxi, and the last bus had left.
Which words can introduce a subordinate clause?
Common words include because for a reason, when, before, after, and until for time, if for a condition, and although for contrast. Choose the word that matches the meaning you want to show. 'Although the café was busy, we found a quiet table' uses although because the two facts contrast.
When the library opens, I will return the books.
When do I use a comma in a complex sentence?
Use a comma after a subordinate clause when it comes before the main clause: 'When the alarm rang, I got up.' When the main clause comes first, a comma is usually unnecessary: 'I got up when the alarm rang.' The comma helps readers identify the opening clause before the main message begins.
The library opens at nine.
Can a subordinate clause stand alone?
Usually, no. A phrase such as 'if the printer stops again' leaves the listener waiting for the result or instruction. Add a main clause to complete the thought: 'If the printer stops again, tell the office manager.' Some short replies use dependent wording in conversation, but full writing usually needs the complete sentence.
If you need help, call the reception desk.