Types of Sentences: Simple, Compound, and Complex
Four sentence structures, sorted by how many clauses they have and how those clauses connect.
Word Origins & Etymology
These categories describe sentence structure — how many clauses a sentence has and how they join. A clause is a group of words with its own subject and verb.
An independent clause can stand alone as a sentence; a dependent (subordinate) clause cannot — it needs an independent clause to lean on.
Count the clauses and check their type. One independent clause = simple; two+ independent = compound; one independent + one+ dependent = complex; two+ independent + one+ dependent = compound-complex.
⚡ Quick Answer
Compound = two or more independent clauses joined (and, but, so, or a semicolon).
Complex = one independent clause + one or more dependent clauses.
Compound-complex = two or more independent clauses + at least one dependent clause.
Memory Trick: Count independent clauses and look for a dependent one. One independent → simple. Two joined → compound. Add a dependent clause → complex (or compound-complex).
🔑 Key Takeaway
An independent clause stands alone; a dependent clause (starting with words like because, when, although, which) cannot. The mix of these two clause types defines the sentence.
| Type | Clauses | Example |
|---|---|---|
| Simple | 1 independent | "She sings." |
| Compound | 2+ independent | "She sings, and he plays." |
| Complex | 1 independent + 1+ dependent | "She sings when she is happy." |
| Compound-complex | 2+ independent + 1+ dependent | "She sings when she is happy, and he plays." |
Quick Comparison
| If the sentence has... | It is... | Clue word |
|---|---|---|
| One subject-verb idea | Simple | (stands alone) |
| Two ideas joined as equals | Compound | and, but, so, or; semicolon |
| One main + one leaning idea | Complex | because, when, although, who |
Simple Sentences
A simple sentence has one independent clause: one subject-verb idea. It can still have compound subjects or objects.
- The dog barked.
- Maria and Tom left early. (compound subject, still simple)
Compound Sentences
A compound sentence joins two or more independent clauses with a coordinating conjunction (for, and, nor, but, or, yet, so — FANBOYS) or a semicolon.
- I wanted to go, but it was raining.
- She studied hard; she passed easily.
Complex Sentences
A complex sentence has one independent clause plus at least one dependent clause (introduced by words like because, when, although, if, who, which).
- Because it was raining, we stayed inside.
- The book that she wrote became a bestseller.
Compound-Complex Sentences
A compound-complex sentence combines both: two or more independent clauses and at least one dependent clause.
- When the bell rang, the students left, and the hall fell silent.
Mixing sentence types keeps writing from feeling choppy or run-on. To avoid the two main errors, see run-on sentences and sentence fragments.
Common Mistakes
Mistake #1: comma splice (two clauses, only a comma)
✗ Wrong: It was late, we went home.
✓ Right: It was late, so we went home. (compound) / It was late; we went home.
Reason: Two independent clauses need a conjunction or semicolon, not just a comma.
Mistake #2: dependent clause left as a sentence
✗ Wrong: Because it was raining.
✓ Right: Because it was raining, we stayed in.
Reason: A dependent clause cannot stand alone; attach it to an independent clause.
Mistake #3: calling a compound subject "compound sentence"
✗ Wrong: "Tom and Lee ran" is a compound sentence.
✓ Right: "Tom and Lee ran" is a simple sentence (one clause, compound subject).
Reason: A compound sentence needs two independent clauses, not just two subjects.
Mistake #4: missing comma before the conjunction
✗ Wrong: She called but no one answered.
✓ Right: She called, but no one answered.
Reason: In a compound sentence, put a comma before the coordinating conjunction.
🎯 Test Your Knowledge
1. "The sun set." is a ____ sentence.
2. "I cooked, and she cleaned." is a ____ sentence.
3. "We left because it was late." is a ____ sentence.
4. Which word signals a dependent clause?
5. "Tom and Lee sang." is which type?
See It Live: Our Engine Flags a Real Mistake
This is the real engine, running locally as you type. The starter sentence is a comma splice; fix the clause join or paste your own.
Expected correction: The meeting ran late, so we missed the train.
Honest limits: the engine flags many comma splices and fragments, but choosing a sentence type is a style decision. Fix the clause structure first, then run the check.
Frequently Asked Questions
What are the four types of sentences by structure?
What is the difference between an independent and a dependent clause?
Is a sentence with "and" always compound?
How do I punctuate a compound sentence?
Real-World Examples
The rain stopped. (simple)
The rain stopped, and the sun came out. (compound)
When the rain stopped, we went outside. (complex)
When the rain stopped, we went outside, and the dog ran ahead. (compound-complex)
Sales rose because demand grew. (complex)
The results were clear; the method was sound. (compound)
It was late, we went home.
Although the test was hard.
Why Sentence Types Get Muddled
The labels hinge on a single distinction — independent vs dependent clause — that is easy to overlook. Writers mistake compound subjects for compound sentences, and dependent clauses for complete ones, which leads straight to comma splices and fragments. Counting the clauses and testing whether each can stand alone clears up the category every time.
Sentence types build on clauses and conjunctions. Reinforce them with the conjunctions list and steer clear of the two big errors in run-on sentences.
Related Articles
- Run-On Sentences — The error from joining clauses incorrectly
- Sentence Fragments — When a dependent clause is left alone
- Conjunctions List — The words that join and subordinate clauses
- Semicolon Usage — Joining independent clauses without a conjunction
- ← View All Grammar Guides
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