English:Simple, Compound, and Complex Sentences
Simple, Compound, and Complex Sentences
Introduction
When you write, you can build sentences in different ways. Some sentences share one complete idea. Others connect two complete ideas. Still others connect a main idea with extra information that cannot stand alone.
In this aiMOOC, you will learn how to recognize and write simple, compound, and complex sentences. You will also learn how clauses, conjunctions, and commas help readers understand your ideas. The goal is not to make every sentence long. The goal is to choose a sentence structure that makes your meaning clear.
By the end, you should be able to explain how the three sentence types are different, combine ideas correctly, fix common sentence errors, and use varied sentence structures in your own writing.
Learning Goals
You will learn to:
- Recognize complete sentences: Check that a group of words expresses a complete thought.
- Identify clauses: Find groups of words with a subject and a verb.
- Spot independent clauses: Decide which clauses can stand alone as sentences.
- Spot dependent clauses: Decide which clauses need another clause to complete their meaning.
- Use conjunctions: Join ideas with suitable coordinating or subordinating conjunctions.
- Use punctuation: Place commas correctly in common compound and complex sentence patterns.
- Vary your writing: Mix sentence types so your paragraphs sound clear and interesting.
The Building Blocks: Clauses
A clause is a group of words that contains a subject and a verb. Clauses are the building blocks you need for understanding sentence structure.
The subject tells who or what the clause is about. The verb tells what the subject does, has, or is.
Example: The puppy barked.
The subject is the puppy. The verb is barked. This group of words also makes sense by itself, so it is an independent clause.
Independent Clauses
An independent clause can stand alone as a complete sentence.
Examples:
Maya reads every night.
The rain stopped.
Our team practiced after school.
Each example has a subject and a verb, and each expresses a complete thought.
Dependent Clauses
A dependent clause also has a subject and a verb, but it does not express a complete thought by itself.
Examples:
because Maya reads every night
when the rain stopped
although our team practiced after school
These groups make you expect more information. A dependent clause needs an independent clause to complete the idea.
Complete examples:
Maya learns new words because she reads every night.
When the rain stopped, we went outside.
Although our team practiced after school, we still felt nervous.
Words such as because, when, although, if, since, while, after, and before often begin dependent clauses. These words are called subordinating conjunctions.
Simple Sentences
A simple sentence has one independent clause and no dependent clause.
Examples:
The cat slept.
My older brother plays the drums.
After lunch, Rosa and Malik cleaned the tables.
The last sentence is still simple. The words After lunch are a phrase, not a clause, because they do not contain both a subject and a verb.
The diagram above shows how the words in the simple sentence I will do my homework can be grouped. You do not need to memorize the labels in the diagram. Notice that all the words work together as one complete clause.
Simple Does Not Mean Short
A simple sentence can be short or long. What matters is the number of independent and dependent clauses.
Short simple sentence: Birds sing.
Longer simple sentence: The bright yellow birds in the tall maple tree sing loudly every morning.
Both have one independent clause.
A simple sentence may also have a compound subject or a compound predicate.
Compound subject: Kim and Pat laugh.
Compound predicate: Kim laughs and waves.
These are still simple sentences because each one contains only one independent clause.
The picture shows Kim and Pat joined by and. Joining two names does not automatically make a compound sentence. You need two independent clauses to make a compound sentence.
Compound Sentences
A compound sentence has two or more independent clauses joined correctly.
Example:
The sun was setting, and we hurried home.
You can split this sentence into two complete sentences:
The sun was setting.
We hurried home.
Because both parts can stand alone, they are independent clauses.
Coordinating Conjunctions
One common way to join two independent clauses is with a comma and a coordinating conjunction.
The seven common coordinating conjunctions can be remembered with the word FANBOYS: for, and, nor, but, or, yet, so.
Examples:
I wanted to ride my bike, but the tire was flat.
We can read the book, or we can listen to the audio version.
The class finished the project, so everyone cleaned the tables.
Punctuation in Compound Sentences
When a coordinating conjunction joins two independent clauses, place a comma before the conjunction.
Correct: Nina packed a snack, and she filled her water bottle.
Not a compound sentence: Nina packed a snack and filled her water bottle.
The second example has one subject, Nina, with two verbs, packed and filled. It is a simple sentence with a compound predicate, so it does not need a comma before and.
A semicolon can also join closely related independent clauses:
The library was quiet; everyone was reading.
For Grades 5–6, focus first on the comma-plus-conjunction pattern. Use the semicolon only when your teacher has introduced it.
Complex Sentences
A complex sentence has one independent clause and at least one dependent clause.
Examples:
We stayed inside because the storm was strong.
When the bell rang, the students packed their bags.
Although the puzzle was difficult, Ava kept trying.
The dependent clause gives extra information such as a reason, time, condition, or contrast.
Subordinating Conjunctions
Subordinating conjunctions help connect a dependent clause to an independent clause.
Useful examples include:
because for a reason
when or before for time
if for a condition
although for contrast
while for time or contrast
since for time or reason
Example with reason: We wore boots because the ground was muddy.
Example with time: Before the movie started, we found our seats.
Example with condition: If the weather stays dry, we will play outside.
Clause Order and Commas
A complex sentence can begin with either the independent clause or the dependent clause.
When the dependent clause comes first, a comma usually separates it from the independent clause.
Dependent clause first: Because the bus was late, we missed the beginning.
When the independent clause comes first, a comma is often not needed before an essential dependent clause.
Independent clause first: We missed the beginning because the bus was late.
The meaning is similar, but changing the order can change which idea gets attention first.
Compare the Three Sentence Types
| Sentence Type | Clause Pattern | Example | What to Notice |
|---|---|---|---|
| Simple | One independent clause | The dog chased the ball. | One complete idea can include many words. |
| Compound | Two or more independent clauses | The dog chased the ball, and the puppy watched. | Both main parts can stand alone. |
| Complex | One independent clause plus at least one dependent clause | The dog chased the ball because it rolled away. | One part can stand alone and one part depends on it. |
A useful test is to look for clauses before you look at sentence length. A long sentence can be simple, and a short sentence can be compound or complex.
A Three-Step Identification Strategy
- Find the verbs: Circle the words that show actions or states of being.
- Find the subjects: Ask who or what is connected to each verb.
- Test the clauses: Decide which clauses can stand alone and which depend on another clause.
Then classify the sentence:
One independent clause means simple.
Two or more independent clauses means compound.
One independent clause plus at least one dependent clause means complex.
Writing with Sentence Variety
Good writing usually mixes sentence structures. If every sentence has the same pattern, a paragraph can sound choppy or repetitive.
Mostly simple:
The rain started. We opened our umbrellas. We walked faster. We reached the museum.
With variety:
The rain started, so we opened our umbrellas. As we walked faster, the wind pushed against us. We reached the museum just before noon.
The second version connects ideas and shows relationships. The compound sentence shows a result, and the complex sentence shows what happened at the same time.
Try to choose sentence structures because they fit your meaning, not just because you want a longer sentence.
Common Mix-Ups and How to Fix Them
Fragment
A fragment is an incomplete group of words that is written as if it were a complete sentence.
Fragment: Because the game ended.
Fixed: We cheered because the game ended.
The first group is a dependent clause. It needs an independent clause.
Run-On Sentence
A run-on sentence joins independent clauses without correct punctuation or a suitable joining word.
Run-on: The game ended we cheered.
Fixed as compound: The game ended, and we cheered.
You could also write two simple sentences: The game ended. We cheered.
Comma Splice
A comma splice happens when two independent clauses are joined only with a comma.
Comma splice: The game ended, we cheered.
Fixed: The game ended, so we cheered.
A comma by itself is not enough to join two independent clauses in this pattern.
Interactive Tasks
Quiz: Test Your Knowledge
Which description matches a simple sentence? (One independent clause) (!Two independent clauses) (!Only a dependent clause) (!No subject or verb)
Which sentence is compound? (The rain stopped, and we went outside.) (!The rain stopped.) (!Because the rain stopped, we went outside.) (!After the rain, we went outside.)
Which sentence is complex? (We stayed inside because the rain was heavy.) (!We stayed inside.) (!We stayed inside, and we played cards.) (!We stayed inside all afternoon.)
What can an independent clause do? (Stand alone as a complete sentence) (!Begin only with because) (!Work only as a sentence fragment) (!Contain no verb)
Which word is a coordinating conjunction? (and) (!because) (!although) (!when)
Which word can begin a dependent clause? (because) (!quickly) (!table) (!bright)
Which punctuation is normally placed before a coordinating conjunction that joins two independent clauses? (A comma) (!An apostrophe) (!A quotation mark) (!A hyphen)
Which sentence is simple even though it has two subjects? (Kim and Pat laugh.) (!Kim laughs, and Pat smiles.) (!When Kim laughs, Pat smiles.) (!Kim laughs because Pat smiles.)
Which sentence correctly begins with a dependent clause? (When the bell rang, we packed our bags.) (!When the bell rang we packed our bags.) (!When the bell rang.) (!The bell rang, we packed our bags.)
Why is the sentence We hurried home because it was getting dark complex? (It has one independent clause and one dependent clause.) (!It has no independent clause.) (!It has two independent clauses only.) (!It has no subject.)
Memory Game
| Simple sentence | A sentence with one independent clause and no dependent clause |
| Compound sentence | A sentence with two or more independent clauses joined correctly |
| Complex sentence | A sentence with one independent clause and at least one dependent clause |
| Independent clause | A clause that can stand alone as a complete sentence |
| Dependent clause | A clause that needs another clause to complete its meaning |
| Coordinating conjunction | A joining word such as and, but, or, or so |
| Subordinating conjunction | A word such as because, when, if, or although that can introduce a dependent clause |
Drag and Drop
| Match the correct terms. | Topic |
|---|---|
| one independent clause | Simple sentence |
| two independent clauses joined correctly | Compound sentence |
| one independent clause and a dependent clause | Complex sentence |
| can stand alone | Independent clause |
| needs another clause | Dependent clause |
...
Crossword Puzzle
| Clause | What group of words contains a subject and a verb? |
| Simple | What sentence type has one independent clause and no dependent clause? |
| Compound | What sentence type joins two or more independent clauses? |
| Complex | What sentence type includes an independent clause and at least one dependent clause? |
| Conjunction | What kind of word can join words, phrases, or clauses? |
| Dependent | What kind of clause cannot usually stand alone as a complete sentence? |
LearningApps
Cloze Text
Open-Ended Tasks
Easy
- Sentence Sort: Write nine sentences, with three simple, three compound, and three complex sentences. Label each type and underline the clauses.
- Conjunction Hunt: Find five conjunctions in a book or school text. Copy the sentences and explain what each conjunction connects.
- Picture Sentences: Choose or draw a picture. Write one simple, one compound, and one complex sentence about the same picture.
- Sentence Repair: Create four fragments or run-ons, trade them with a partner, and correct each other’s sentences.
Standard
- Comic Strip Writing: Create a six-panel comic and write captions that include at least two simple, two compound, and two complex sentences.
- Interview and Report: Interview a classmate about a hobby, then write a short report that uses all three sentence types.
- Sentence Combining Challenge: Start with eight short simple sentences and combine them into a smoother paragraph without changing the main facts.
- Grammar Video: Record a one-minute teaching video that explains the difference between a compound sentence and a complex sentence using your own examples.
Advanced
- Paragraph Makeover: Take a paragraph with repetitive sentence patterns, revise it for sentence variety, and explain why you changed each sentence.
- School Writing Survey: Collect ten sentences from school-safe texts, classify their structures, and create a chart showing how often each type appears.
- Conjunction Experiment: Write one pair of ideas and connect it in at least four different ways. Explain how changing the conjunction changes the relationship between the ideas.
- Mini Grammar Guide: Design a one-page guide for younger students that teaches clauses, the three sentence types, punctuation, and at least six original examples.
Learning Assessment
- Sentence Classification Assessment: Classify a mixed set of sentences and justify each answer by identifying the independent and dependent clauses.
- Sentence Combining Assessment: Combine pairs of related ideas into simple, compound, or complex sentences and explain why each structure fits the meaning.
- Editing Assessment: Correct fragments, run-ons, comma splices, and missing commas in a short paragraph, then explain at least three corrections.
- Writing Transfer Assessment: Write a paragraph about a new topic that uses all three sentence types accurately and naturally.
- Meaning and Conjunction Assessment: Compare sentences joined with different conjunctions and explain how the relationship between ideas changes.
- Revision Assessment: Revise a repetitive paragraph for sentence variety while keeping its facts and main message the same.
Evidence of Learning
Your work should show not only that you remember definitions, but that you can use sentence structures to communicate clearly.
| Area | Evidence |
|---|---|
| Knowledge | You can explain independent and dependent clauses and describe simple, compound, and complex sentences. |
| Skills | You can identify clauses, choose suitable conjunctions, use common comma patterns, combine ideas, and correct fragments or run-ons. |
| Products | You can produce labeled examples, revised paragraphs, comics, short reports, charts, grammar guides, or teaching videos. |
| Transfer | You can use sentence variety in stories, reports, explanations, emails, science writing, social studies writing, and other school tasks. |
OERs on the Topic
The following English Wikipedia page gives a more advanced overview of how sentences can be classified by their clause structure. Use it when you want to go beyond the examples in this course.
Linked Learning Areas