- A compound sentence joins two independent clauses using a coordinating conjunction (FANBOYS) or a semicolon.
- The seven FANBOYS are: For, And, Nor, But, Or, Yet, So — each showing a different logical relationship.
- Place a comma before the coordinating conjunction when joining two full independent clauses.
- Avoid comma splices (two clauses joined only by a comma) and run-on sentences (no punctuation at all).
- Compound sentences differ from complex sentences, which use subordinating conjunctions and dependent clauses.
If you have ever been told that your writing sounds choppy or repetitive, compound sentences are almost certainly the answer. At B1 level and beyond, the ability to join ideas fluently across a single sentence — rather than listing short, disconnected statements — is one of the clearest signs of a developing writer. And yet compound sentences trip up learners at every stage, because the rules around commas, conjunctions, and semicolons are more precise than they first appear.
This complete guide covers everything you need to master compound sentences: what they are and how they work, the seven FANBOYS coordinating conjunctions with individual explanations and examples, how and when to use semicolons as an alternative, where exactly to place the comma, the two most common errors learners make (comma splices and run-on sentences), how compound sentences compare to complex and compound-complex structures, and a set of practice exercises with full answers. Let us start from the beginning.
1. What Is a Compound Sentence?
A compound sentence consists of two or more independent clauses joined together. An independent clause is a group of words that contains a subject and a verb and expresses a complete thought — in other words, it could stand alone as its own sentence.
She studied all night. + She passed the exam.
These two independent clauses can be combined into a single compound sentence in several ways:
She studied all night, so she passed the exam.
She studied all night; she passed the exam.
She studied all night, and she passed the exam.
The key feature of a compound sentence is that the two clauses are grammatically equal. Neither is dependent on the other. Both express a complete idea. This equal relationship is what distinguishes compound sentences from complex sentences, which we will explore in Section 6.
Compound sentences are essential for creating variety and flow in writing and speech. They allow you to show logical connections between ideas — cause and effect, contrast, addition, alternatives — without always starting a new sentence. Visit our grammar section for a full overview of English sentence types at every level.
2. The 7 FANBOYS Coordinating Conjunctions Explained
FANBOYS is a mnemonic that stands for the seven coordinating conjunctions in English: For, And, Nor, But, Or, Yet, So. Each one expresses a different relationship between the two clauses it connects. Learning each one individually — rather than treating them as interchangeable — will dramatically improve the precision of your writing.
For — Reason
"For" introduces a reason or cause, similar to "because" but more formal. It is rarely used in spoken English today.
Example: She wore a coat, for the wind was bitter.
And — Addition
"And" adds one idea to another. Both clauses point in the same direction.
Example: He finished the report, and he sent it to his manager.
Nor — Negation
"Nor" joins two negative clauses. After "nor", the subject and auxiliary verb are inverted.
Example: She did not call, nor did she send a message.
But — Contrast
"But" shows contrast or an unexpected result. It is one of the most frequently used conjunctions.
Example: I wanted to sleep, but the noise kept me awake.
Or — Alternative
"Or" presents a choice or alternative between two clauses.
Example: You can take the bus, or you can walk to the station.
Yet — Concession
"Yet" is similar to "but" but adds a sense of surprise — the second clause is unexpected given the first.
Example: She had very little time, yet she completed every task.
So — Result
"So" introduces a result or consequence of the first clause. It is the coordinating equivalent of "therefore".
Example: The map was unclear, so we took the wrong road.
Say FANBOYS out loud as one word. Once you have the list memorised, quiz yourself by generating one example sentence for each conjunction. Vary your topics each time so you reinforce both the grammar and new vocabulary simultaneously.
3. Using Semicolons to Join Independent Clauses
A semicolon (;) offers an alternative to FANBOYS conjunctions. When two independent clauses are closely related in meaning, you can join them with a semicolon alone — no conjunction needed. The semicolon signals a closer relationship than a full stop (period) but a slightly longer pause than a comma.
The presentation was a success; the audience applauded for two minutes.
She loves early mornings; I never get up before nine.
You can also combine a semicolon with a conjunctive adverb — words such as however, therefore, moreover, consequently, nevertheless, furthermore. When you do this, place the semicolon before the conjunctive adverb and a comma after it:
The budget was cut; however, the project continued on schedule.
He worked very hard; therefore, he deserved the promotion.
Semicolons create a more formal and balanced tone than conjunctions. They work best in formal writing, essays, and professional correspondence. In informal writing, conversation, and most everyday contexts, a FANBOYS conjunction is usually the better choice. For more on punctuation in context, explore the LexFizz blog for related grammar articles.
4. Punctuation Rules: Where to Place the Comma
Knowing where to put the comma in a compound sentence is one of the most frequently tested punctuation skills at B1 level. The rule is straightforward, but learners often apply it incorrectly in both directions — adding commas where none are needed, or omitting them where they are required.
Rule: Place a comma before the coordinating conjunction when it joins two independent clauses.
I finished my homework, and I watched a film.
The sky was clear, but the temperature was low.
She could stay at home, or she could visit her friend.
No comma is needed when the conjunction joins two words, two phrases, or two items in a simple list — not two full independent clauses:
She sings and dances. (no comma — "dances" has no subject)
You can have tea or coffee. (no comma — two nouns, not two clauses)
| Structure | Comma? | Example |
|---|---|---|
| Conjunction joins two independent clauses | Yes | I was hungry, so I made a sandwich. |
| Conjunction joins two verbs, same subject | No | She opened the door and walked in. |
| Conjunction joins two nouns or adjectives | No | He is tall and confident. |
| Semicolon alone (no conjunction) | No comma needed | It was late; we left immediately. |
| Semicolon + conjunctive adverb | Comma after adverb | It was late; however, we stayed. |
5. Common Mistakes: Comma Splices and Run-On Sentences
Two errors dominate learner writing at B1 level when it comes to joining independent clauses. Knowing their names — and how to fix them — gives you a clear framework for self-editing.
The Comma Splice
A comma splice occurs when two independent clauses are joined using only a comma, with no coordinating conjunction.
Wrong: I was tired, I went to bed early.
Wrong: The exam was difficult, many students failed.
Fix a comma splice using one of three methods:
- Add a FANBOYS conjunction: I was tired, so I went to bed early.
- Replace the comma with a semicolon: I was tired; I went to bed early.
- Write two separate sentences: I was tired. I went to bed early.
The Run-On Sentence
A run-on sentence (also called a fused sentence) occurs when two independent clauses are written together with no punctuation or conjunction at all.
Wrong: She loves coffee she drinks three cups a day.
Wrong: The film was long we didn't leave until midnight.
Apply the same three fixes: add a coordinating conjunction with a comma, insert a semicolon, or split into two sentences. Developing the habit of checking every sentence for a subject and verb is the fastest way to catch both errors in your own writing. Our grammar exercises include dedicated comma splice and run-on drills.
6. Compound vs Complex vs Compound-Complex Sentences
Understanding how compound sentences differ from other sentence types helps you choose the right structure for the meaning you want to express.
| Type | Structure | Key words | Example |
|---|---|---|---|
| Simple | One independent clause | (none) | She passed the exam. |
| Compound | Two+ independent clauses | FANBOYS / semicolon | She studied hard, and she passed the exam. |
| Complex | One independent + one dependent clause | because, although, when, if, since, unless | She passed the exam because she studied hard. |
| Compound-complex | Two+ independent clauses + one+ dependent clause | FANBOYS + subordinating conjunction | She studied hard, and she passed the exam, although it was very difficult. |
The critical distinction between compound and complex sentences is the type of relationship between the clauses. In a compound sentence, both clauses are equal — removing either one leaves a perfectly good sentence. In a complex sentence, the dependent clause cannot stand alone; it depends on the main clause for its meaning.
Skilled writers mix all four sentence types to create rhythm and emphasis. A short simple sentence after two longer compound or complex sentences creates impact. Read your writing aloud and notice where every sentence feels the same length — that is usually where variety would help most.
A compound-complex sentence combines at least two independent clauses (compound) with at least one dependent clause (complex). These are powerful structures but require careful punctuation. For a full guide to complex sentence patterns, see our grammar resources.
7. Practice Exercises with Answers
Use these exercises to test and consolidate your understanding. Try each one before reading the answer.
Exercise 1: Choose the Correct FANBOYS Conjunction
Fill in the blank with the most logical coordinating conjunction from FANBOYS:
- I wanted to call you, _____ my phone battery died. (contrast / reason)
- She practised every day, _____ her pronunciation improved significantly.
- You can study tonight, _____ you can leave it until tomorrow morning.
- He did not enjoy the meal, _____ did he finish what was on his plate.
- The weather was cold, _____ we decided to go for a walk anyway.
1. but (contrast) | 2. so (result) | 3. or (alternative) | 4. nor (negation) | 5. yet (concession/surprise)
Exercise 2: Identify and Fix the Error
Each sentence below contains either a comma splice, a run-on sentence, or correct punctuation. Identify the error and write a corrected version.
- The library was closed, we couldn't return the books.
- She ordered a coffee and a sandwich and ate them at her desk.
- It was raining heavily we cancelled the outdoor event.
- He worked late, but he still finished on time.
- The report was good, it could have been more detailed.
1. Comma splice → "The library was closed, so we couldn't return the books." | 2. Correct (two verbs, same subject — no comma needed) | 3. Run-on → "It was raining heavily; we cancelled the outdoor event." | 4. Correct | 5. Comma splice → "The report was good, but it could have been more detailed."
Exercise 3: Combine the Sentences
Join each pair of simple sentences into one compound sentence using an appropriate FANBOYS conjunction or semicolon:
- The train was delayed. We arrived an hour late.
- She speaks French. She speaks Spanish.
- You should save your work regularly. You might lose progress.
- The film received poor reviews. It was a box-office success.
1. "The train was delayed, so we arrived an hour late." | 2. "She speaks French; she also speaks Spanish." | 3. "You should save your work regularly, or you might lose progress." | 4. "The film received poor reviews, but it was a box-office success."
Ready to Practise More?
Reinforce compound sentence skills with LexFizz interactive grammar exercises — sentence combining, error correction, and gap-fills designed for B1 learners.
Start Exercises →Frequently Asked Questions
What is a compound sentence?
A compound sentence joins two or more independent clauses using a coordinating conjunction (FANBOYS), a semicolon, or a semicolon followed by a conjunctive adverb. Each clause has its own subject and verb and can stand alone as a sentence. Example: "She studied hard, and she passed the exam."
What does FANBOYS stand for?
FANBOYS is a mnemonic for the seven coordinating conjunctions in English: For, And, Nor, But, Or, Yet, So. Each one shows a different relationship between the two clauses it joins — reason, addition, negation, contrast, choice, concession, and result respectively.
Do you always put a comma before a coordinating conjunction in a compound sentence?
Yes, when a coordinating conjunction joins two independent clauses, a comma is placed before the conjunction. For example: "I wanted to leave early, but the meeting ran late." However, if the conjunction joins only two words or phrases (not full clauses), no comma is used: "She sings and dances."
What is a comma splice and how do I fix it?
A comma splice is the error of joining two independent clauses with only a comma and no conjunction. Example (wrong): "I was tired, I went to bed." Fix options: (1) add a coordinating conjunction — "I was tired, so I went to bed"; (2) use a semicolon — "I was tired; I went to bed"; (3) make two separate sentences.
What is a run-on sentence?
A run-on sentence occurs when two or more independent clauses are joined without any punctuation or conjunction at all. Example (wrong): "She loves coffee she drinks three cups a day." This can be fixed by adding a coordinating conjunction with a comma, a semicolon, or splitting into two sentences.
When should I use a semicolon instead of FANBOYS?
Use a semicolon when the two independent clauses are closely related in meaning and you want a closer connection than a period but no explicit conjunction. Semicolons create a more formal, balanced effect. Example: "The rain was heavy; the streets flooded quickly." You can also follow the semicolon with a conjunctive adverb such as however, therefore, or moreover.
What is the difference between a compound sentence and a complex sentence?
A compound sentence joins two independent clauses of equal grammatical weight with a coordinating conjunction. A complex sentence joins one independent clause with one or more dependent (subordinate) clauses using a subordinating conjunction such as because, although, when, or if. Example compound: "She was late, but she apologised." Example complex: "Although she was late, she apologised."
What is a compound-complex sentence?
A compound-complex sentence contains at least two independent clauses AND at least one dependent clause. It combines the structures of both compound and complex sentences. Example: "I wanted to go to the party, but I stayed home because I had a headache." This sentence has two independent clauses joined by "but" and one dependent clause beginning with "because".
Can I start a sentence with a coordinating conjunction like "And" or "But"?
In informal and creative writing, starting a sentence with And, But, or So is widely accepted and can be an effective stylistic choice for emphasis. In formal academic writing, it is generally better to use transition phrases such as "In addition," "However," or "As a result," instead. Follow the style guide or context appropriate to your writing task.
How can I practise writing compound sentences?
Good practice strategies include: (1) Take simple sentences you have written and combine pairs using each FANBOYS conjunction in turn; (2) Rewrite paragraphs from a text by joining or splitting sentences to create variety; (3) Complete gap-fill and sentence-combination exercises on LexFizz; (4) Edit your own writing to check that every compound sentence has a comma before the conjunction and no comma splices.