Complex Sentences & Clauses
Learn how to build powerful sentences by combining main clauses with subordinate clauses.
Three Types of Sentences
Sentences come in different levels of complexity. Understanding these types helps you write with more variety and sophistication.
Simple Sentence
Contains one main clause with a subject and a verb.
The cat sat on the mat.
Compound Sentence
Two main clauses joined by a coordinating conjunction (and, but, or, so).
The cat sat and the dog slept.
Complex Sentence
A main clause and one or more subordinate clauses.
Although it was raining, the cat sat on the mat.
Main Clause vs Subordinate Clause
A clause is a group of words that contains a subject and a verb. The key difference between a main clause and a subordinate clause is whether it can stand alone as a sentence.
Main Clause (Independent)
Makes complete sense on its own. It can stand alone as a sentence.
- ✓ The children played outside.
- ✓ She finished her homework.
- ✓ The sun was shining brightly.
Subordinate Clause (Dependent)
Does not make complete sense on its own. It needs a main clause.
- ✗ because it was sunny
- ✗ although she was tired
- ✗ when the bell rang
Top Tip: The "Makes Sense" Test
Read the clause aloud. If it sounds like a complete thought, it is a main clause. If it feels incomplete or leaves you wondering "what happened next?", it is a subordinate clause.
Subordinating Conjunctions
Subordinating conjunctions are the words that start a subordinate clause. They show the relationship between the two clauses (time, reason, contrast, condition).
because (reason)
She wore a coat because it was cold.
although / even though (contrast)
Although he studied hard, he found the test difficult.
when / while / after / before (time)
When the rain stopped, we went outside.
if / unless (condition)
If you practise every day, you will improve.
so that / in order to (purpose)
He ran fast so that he would not be late.
Comma Rule
When the subordinate clause comes first, use a comma before the main clause.
Colour-Coded Sentence Diagrams
See how complex sentences are built by combining clauses. Main clause Subordinate clause Conjunction
Example 1 (subordinate clause at the end)
The dog barked loudly because a stranger was at the door.
Example 2 (subordinate clause at the start — note the comma)
While the teacher was talking, the students listened carefully.
Example 3 (subordinate clause in the middle)
The boy, who was very hungry, ate his lunch quickly.
Key Vocabulary
Clause
A group of words containing a subject and a verb.
Main Clause
A clause that makes complete sense on its own; also called an independent clause.
Subordinate Clause
A clause that depends on a main clause and cannot stand alone; also called a dependent clause.
Subordinating Conjunction
A word that introduces a subordinate clause (because, although, when, if, while).
Coordinating Conjunction
A word that joins two main clauses in a compound sentence (and, but, or, so).
Complex Sentence
A sentence containing a main clause and at least one subordinate clause.
Worked Examples
See how simple sentences can be combined into complex sentences.
Example 1: Combining with "because"
Simple sentences: I brought an umbrella. It was raining.
Complex sentence: I brought an umbrella because it was raining.
The subordinate clause explains the reason.
Example 2: Combining with "although"
Simple sentences: The film was long. We enjoyed it.
Complex sentence: Although the film was long, we enjoyed it.
The subordinate clause shows contrast. Notice the comma after the subordinate clause.
Example 3: Combining with "if"
Simple sentences: You eat your vegetables. You can have dessert.
Complex sentence: If you eat your vegetables, you can have dessert.
The subordinate clause states a condition.
Knowledge Check
Test your understanding of complex sentences and clauses. Select the correct answer and click "Check Answer".
Question 1
Which of the following is a subordinate clause?
Question 2
What type of sentence is this? "The children played outside and the adults stayed inside."
Question 3
Which conjunction would best complete this complex sentence? "___ it was getting dark, we decided to go home."
Question 4
In the sentence "When the bell rang, the students packed up their bags", which is the main clause?
Question 5
Where should you place a comma in a complex sentence?
Key Concepts Summary
- ● A simple sentence has one main clause. A compound sentence has two main clauses joined by "and", "but", "or", or "so".
- ● A complex sentence has a main clause and at least one subordinate clause.
- ● A main clause makes sense on its own. A subordinate clause does not.
- ● Subordinating conjunctions (because, although, when, while, if) introduce subordinate clauses.
- ● Use a comma after the subordinate clause when it comes first in the sentence.