Compound and Complex Sentences
Grade 4 · English · Study Guide
Learn how to combine simple sentences into compound and complex sentences to make your writing more sophisticated.
Sentences come in different types, and knowing how to use them all makes your writing much more interesting and mature. We'll focus on compound and complex sentences — two key types that go beyond simple sentences.
A simple sentence has one independent clause — one subject, one predicate, one complete thought. 'The bird sang' is a simple sentence. A compound sentence joins two or more independent clauses using a coordinating conjunction (and, but, or, nor, for, yet, so) or a semicolon. 'The bird sang AND the sun rose' is a compound sentence — two complete thoughts joined by 'and.'
The coordinating conjunctions can be remembered with the acronym FANBOYS: For, And, Nor, But, Or, Yet, So. Each one connects two equal, independent ideas. 'She wanted to sleep, but she had homework to finish' is a compound sentence using 'but.'
A complex sentence has one independent clause and at least one dependent clause. A dependent clause has a subject and verb but does NOT express a complete thought on its own — it depends on the independent clause. 'Because it was raining, we stayed inside' is a complex sentence. 'Because it was raining' is the dependent clause — it can't stand alone.
Subordinating conjunctions connect dependent clauses to independent clauses. Common ones include: because, although, while, when, if, since, until, before, after, and unless. When the dependent clause comes FIRST, put a comma after it. When it comes SECOND, no comma is needed.
| Type | Structure | Example |
|---|---|---|
| Simple | 1 independent clause | The dog barked. |
| Compound | 2 independent clauses + FANBOYS | The dog barked, and the cat ran. |
| Complex | 1 independent + 1 dependent clause | Although it rained, we played outside. |
Key terms
- Independent clause
- A group of words with a subject and verb that expresses a complete thought and can stand alone
- Dependent clause
- A group of words with a subject and verb that does NOT express a complete thought alone
- Compound sentence
- Two independent clauses joined by a coordinating conjunction or semicolon
- Complex sentence
- An independent clause joined with a dependent clause using a subordinating conjunction
- FANBOYS
- Memory trick for coordinating conjunctions: For, And, Nor, But, Or, Yet, So
Flashcards
- Simple Sentence
- One independent clause — one complete thought: 'The cat slept.'
- Compound Sentence
- Two independent clauses joined by a FANBOYS conjunction: 'I was tired, but I kept going.'
- Complex Sentence
- One independent + one dependent clause: 'Because it rained, we stayed inside.'
- Independent Clause
- A complete thought that can stand alone as a sentence
- Dependent Clause
- Has subject + verb but can't stand alone — starts with a subordinating conjunction
- FANBOYS
- Coordinating conjunctions: For, And, Nor, But, Or, Yet, So
Practice questions
Which sentence is a compound sentence?
- The cat slept.
- Because she was tired, she napped.
- I wanted pizza, but we had sandwiches.
- Running through the park is fun.
Show answer
Answer: I wanted pizza, but we had sandwiches.
Two independent clauses ('I wanted pizza' and 'we had sandwiches') joined by the coordinating conjunction 'but' — that's a compound sentence.
A dependent clause can stand alone as a complete sentence.
Show answer
Answer: False
A dependent clause needs an independent clause to complete its meaning — 'Because she was tired' leaves you waiting for more.
The acronym FANBOYS helps remember the ___ conjunctions.
Show answer
Answer: coordinating
FANBOYS = For, And, Nor, But, Or, Yet, So — these are the seven coordinating conjunctions.
Which word makes 'She studied hard ___ she wanted to pass the test' a complex sentence?
- and
- but
- because
- so
Show answer
Answer: because
'Because' is a subordinating conjunction that introduces a dependent clause, creating a complex sentence.
When a dependent clause begins a complex sentence, a comma is placed after it.
Show answer
Answer: True
When the dependent clause leads: 'Because it was late, we left.' — the comma separates it from the independent clause.
Fun facts
- The FANBOYS acronym has been taught to American students since at least the 1950s — it's one of the most enduring grammar memory tricks ever invented!
- Ernest Hemingway was famous for writing mostly short, simple sentences on purpose. Marcel Proust, on the other hand, wrote a sentence in his novel that is over 900 words long — that's a very complex sentence!
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