What is a Compound Sentence and How to Write One?

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In English, we categorize sentences into four types on the basis of their structure (number of dependent and independent clauses): simple, compound, complex, and compound-complex. Using different types of sentences adds variety to our writing, with the latter three combining multiple ideas to convey complex message.

In this post, we’ll cover compound sentence.

Learn the other three types:

What is a compound sentence?

A compound sentence, also called coordinate sentence, is a sentence that contains at least two independent clauses and no dependent clause.

Here is a brief summary of number of dependent and independent clauses in the four types of sentences.

(Feel free to use this image for own use, using the above link for attribution.)

And here is the same information in graphical form, which will make it abundantly clear that there is no overlap between the four types of sentences (none of the dots cross paths).

(Feel free to use this image for own use, using the above link for attribution.)

These sentences, though, differ beyond just the two types of clauses they contain. Learn how compound and complex sentences differ in the meaning they convey:

A sentence is essentially a combination of clauses, with the simplest of them containing an independent clause.

Tom hit the ball hard. [Independent clause]

If we add an independent clause to it, we get a compound sentence.

Tom hit the ball hard, but he couldn’t clear the fence. [Independent clause + Independent clause = Compound sentence]

See more examples of compound sentences:

We can add another independent clause, but the sentence will remain a compound sentence. Remember, a compound sentence contains two or more independent clauses.

Tom hit the ball hard, but he couldn’t clear the fence, so he tried even harder the next time. [Independent clause + Independent clause + Independent clause = Compound sentence]

If we add a dependent clause to the last two sentences, they’ll cease to be a compound sentence. This, for example, is no longer a compound sentence.

Even though Tom was dead tired, he hit the ball hard, but he couldn’t clear the fence. [Independent clause + Independent clause + Dependent clause (Adverb clause)]

There is absolutely no place for a dependent clause in a compound sentence.

The fundamental of forming a compound sentence is to join independent clauses. If you noticed, we joined them in the above sentences through a coordinating conjunction (but, so, etc., also known by the acronym FANBOYS) But that’s not the only way. You can join independent clauses in three different ways – coordinating conjunction, semicolon, and colon – with the latter two much less in use than the first.

Let’s consider each.

1. How to write a compound sentence using coordinating conjunction?

Two or more independent clauses can be joined using a comma followed by one of seven coordinating conjunctions, also called FANBOYS. This is the most common way to write compound sentences. Note the comma and the coordinating conjunction but in this example.

Susan woke up late. [Independent clause 1]

She managed to reach office in time. [Independent clause 2]

Susan woke up late, but she managed to reach office in time. [Compound sentence]

More examples:

The new Covid guidelines require mandatory vaccination for all businesses with more than 100 employees, or they require them to take weekly Covid tests.

Collision by an asteroid of even few hundred meters can cause apocalyptic harm to humans and the planet, so scientists are mapping each and every near-earth asteroid of significant size.

Cows grazed, and flowers waved in the gentle breeze, and the bees buzzed over the flowers. [You can drop the first and as it’s a list of independent clauses, much like list of items (example: mangoes, oranges, and apples).]

1.1 These are not compound sentences though

These are not compound sentences though because they no longer contain two independent clauses: The underlined parts don’t have a subject and hence are not independent clauses. Remember, an independent clause must have its own subject-verb unit.

Susan woke up late but managed to reach office in time.

The new Covid guidelines require mandatory vaccination for all businesses with more than 100 employees or require them to take weekly Covid tests.

Since the subject was common in the two independent clauses in both the sentences, we pulled one of them out, thereby reducing the count of independent clauses in each sentence to one. The first sentence, for example, now contains one independent clause with the subject Susan and a compound predicate with two verbs. We’ve also removed the comma because the sentences no longer have two independent clauses. See more such sentences and decide whether they’re simple or compound.

From the perspective of writing, the above two sentences are better than their compound counterparts as they don’t repeat the subject unnecessarily. Even one word less matters. So, unless you’re asked specifically to write compound sentences, which wouldn’t be the case in real pieces of writing, prefer non-compound version if the subject is common in the two independent clauses. Note that you can’t reduce the third compound sentence to the above form because the two independent clauses have different subjects.

This is a compound sentence, though it may look like the last two sentences.

Use compound-complex sentences by all means, but expand your repertoire of complex sentences.

The two independent clauses are imperative sentences, with the implied subject you. The above sentence is essentially this.

You use compound-complex sentences by all means, but you expand your repertoire of complex sentences.

1.2 Punctuation

A. Comma can be dropped if the independent clauses are short

The general rule in writing compound sentences using coordinating conjunction is to use a comma before the coordinating conjunction. But when the independent clauses are short, some writers omit comma. Examples:

Jane likes pizza and she also likes pasta.

You could stay or you could go.

Vegetables are packed with vitamins and that’s important.

B. Comma may be used to bring clarity to non-compound sentences with compound predicate

Comma may be used to bring clarity to a sentence even if the coordinating conjunction doesn’t join two independent clauses. Examples:

The relative pronoun which is used to refer to animals and things, and is arguably the most-used of the seven. [Absence of comma would result in two ands in succession, creating some confusion.]

The traffic police are ensuring better compliance of traffic rules by information campaigns in medium to large organizations, and hauling up the violators even for seemingly insignificant violation. [Without comma, a reader may be strained to locate the boundary between the two parts of the predicate because of the long string of words before and.]

Some authors and publications, however, have their own style guide, which may depart from the conventional rules. These sentences from The Elements of Style Workbook by William Strunk Jr., for example, use a comma before the coordinating conjunction, even though it doesn’t join two independent clauses.

This style expresses a greater degree of excitement, and a deeper current of feeling than the forcible style.

Thunder accompanies a rainstorm, but is neither a cause nor a result of it.

It works for them as they’ve reputation to go with it, but for others it may be taken as mispunctuation.

C. How to punctuate if the second independent clause has an introductory phrase?

How do you punctuate the compound sentence formed out of these two independent clauses?

Ghosts are regular to this building.

According to some accounts, they’re seen mostly before midnight. [Independent clause with an introductory phrase]

Compound sentence formed out of the above independent clauses is punctuated in two ways.

Ghosts are regular to this building, and, according to some accounts, they’re seen mostly before midnight.

Ghosts are regular to this building, and according to some accounts, they’re seen mostly before midnight.

The first, which treats the introductory phrase as an aside, suffers from too many commas. The second has a comma fewer, a preferred option in modern usage. This option also finds support from compound-complex sentences with similar structure, which follow similar punctuation. An example:

The lawyer argued. [Independent clause]

Because the petition was not properly drafted, the judge rejected the plea. [Complex sentence]

The lawyer argued, but because the petition was not properly drafted, the judge rejected the plea. [Compound-complex sentence. When we combine the above two to form this sentence, comma is not used after but.]

So, the second option of fewer commas is better.

The comma rule in such cases can be summarized as: When the second independent clause starts with an introductory phrase, join it to the first independent clause with a comma followed by a coordinating conjunction, retaining the comma after the introductory phrase.

Can you improve the punctuation in this sentence from Virat Kohli, the former captain of Indian men’s cricket team?

Everything has to come to a halt at some stage and for me as Test captain of India, it’s now. Source

One comma is alright; put another before and.

2. How to write a compound sentence using semicolon?

Two or more closely related independent clauses can be joined with a semicolon to form a compound sentence. Examples:

Talking is easy; doing is difficult.

Luck isn’t divine; it can be created through diligent work.

Susan wasn’t happy with all the clutter on her table; however, she proceeded with day’s work. [Sentences with conjunctive adverbs such as however automatically qualify for use of semicolon as they imply close relation between two independent clauses.]

Traditionally, grants and debt have been the most preferred financial instruments for aid-projects; equity, guarantees, and other instruments have found relatively less adoption.

Since a semicolon can join only closely related independent clauses, this method can be used only sparingly to write compound sentences.

2.1 These are not compound sentences though

Semicolon can’t be used to connect any two independent clauses; they should be closely related. These sentences, for example, aren’t correct because the constituent independent clauses are not closely related.

Talking is easy; talking too much can land one in trouble.

Luck isn’t divine; it can desert you at the most inopportune time.

This too isn’t a compound sentence because it contains only one independent clause.

The future of workplace: Data shows that working remotely is growing.

2.2 Punctuation

Punctuation is straightforward when combining independent clauses with a semicolon. Separate the two clauses by a semicolon, with the second and subsequent clauses starting with a lower-case letter. To separate three clauses, add another semicolon.

3. How to write a compound sentence using colon?

Two independent clauses can be joined with a colon to form a compound sentence if the second independent clause (the one after the colon) explains or expands on the first. Examples:

The proverb Don’t bite off more than you can chew also applies to study: Studying in small, manageable chunks helps you grasp better.

People are generally more productive in the morning: They’re fresh after night’s sleep; second, there are fewer distractions in the morning. [Three independent clauses, with the second and third explaining the first]

Since a colon can join only those independent clauses in which one explains or expands on the other, this method can be used only sparingly to write compound sentences.

3.1 These are not compound sentences though

These two sentences are incorrect because you can’t use a colon where the second independent clause doesn’t explain the first.

The proverb Don’t bite off more than you can chew also applies to study: Studying in the morning help some grasp better.

People are generally more productive in the morning: I leave for office by 8 AM.

This sentence is correct, but it contains just one independent clause and hence is not compound. (A colon doesn’t need to have independent clauses on both the side.)

Within few years of iPhone’s launch, employees at RIM started keeping two phones: a BlackBerry for the workplace and an iPhone for personal use.

3.2 Punctuation

Punctuation is straightforward when combining independent clauses with a colon. The colon follows the first independent clause and is followed by the independent clause that explains or expands on the first. Though style guides differ on capitalizing the first word in the second independent clause, capitalization is widely recommended and used.

Let’s apply what we’ve covered so far in writing few compound sentences.

Exercise: Write compound sentences

Combine the two independent clauses to form a compound sentence. Use semicolon or colon wherever the condition for using them exists.

1. The ruling party came back to power. It bagged fewer seats this time.

2. I didn’t do well in math. My teacher asked me to take remedial classes.

3. His reason for working in a small company was simple. Better be the head of a dog than the tail of a lion.

4. You should pay your pending instalments. The bank officials may initiate legal action.

5. We looked at the first type earlier. Let’s look at the second type now.

Answers to Exercise

1. The ruling party came back to power, but it bagged fewer seats this time.

2. I didn’t do well in math, so my teacher asked me to take remedial classes.

3. His reason for working in a small company was simple: Better be the head of a dog than the tail of a lion.

4. You should pay your pending instalments, or the bank officials may initiate legal action.

5. We looked at the first type earlier; let’s look at the second type now.

How to identify a compound sentence?

Identifying a sentence as compound, and for that matter any of the four types of sentences, is essentially about identifying the number and type of clauses in it. If the sentence contains two or more independent clauses, it is compound. So, look for FANBOYS or semicolon or colon, which would hint at multiple independent clauses. Second, rule out even one dependent clause in the sentence.

This, however, is easier said than done. Try identifying the type of these sentences.

Insurance companies allow people to take their plan at almost any age but steadily increase monthly payments with age.

The storm barreled through the town, uprooting trees and damaging buildings, but the church I visit didn’t suffer any significant damage.

The first is simple and the second is compound-complex (I visit is a dependent clause). Identifying dependent and independent clauses is an exercise in itself and can’t be covered in the limited space here.

Get better at identifying clauses in a sentence:

Common errors in writing compound sentences

1. Joining without FANBOYS

Unless you’re joining independent clauses with colon or semicolon, you must use a coordinating conjunction. These, for example, can’t stand as sentences, let alone as compound sentences.

Susan woke up late, she managed to reach office in time. [Joined by comma alone. Such error is called comma splice]

Susan woke up late she managed to reach office in time. [Joined by nothing. Such error is called fused sentence]

More resources:

2. Joining with non-FANBOYS

A common error students make is to combine two independent clauses with a comma (sometimes with two or none) followed by a non-FANBOYS word. The most common such words are conjunctive adverbs such as therefore, however, hence, otherwise, instead, now, and next. Conjunctive adverbs, however, are used differently and can’t be used like FANBOYS. These, for example, are incorrect.

I plan to go to the market in the evening, now I have to finish other work.

The results of the study were inconclusive, therefore more research needs to be done on the topic.

We should avoid using single-use plastic carry bags, instead we should use jute bags.

The teacher checked our homework, then she gave us a new assignment.

All four are in fact comma splice errors as the parts after comma are independent clauses.

3. Missing the comma or putting unnecessary comma

Unlike the first two errors, these are minor but are still noticed.

It’s common to see two independent clauses joined by a coordinating conjunction but without comma. A case in point is this sentence from the statement of CEO of SII, world’s largest manufacturer of vaccines.

That is our endeavor too and we are making every effort to achieve that.

Maybe they follow a different style guide, but I doubt it as the same statement contains a far egregious comma splice error.

It’s also common to see a comma between two parts of a sentence (that are not independent clauses) joined by FANBOYS.

Susan woke up late, but managed to reach office in time.

As discussed earlier, both have exceptions, but one should stick to the convention outside exceptions.

What implications do compound sentences hold for your writing?

Compound sentences serve a purpose. They join two or more ideas of equal weight, expressing relationship between them while adding variety to your writing.

Compound sentences have fans, especially among students. And why not? They’re simple to write. They’ve limited number of connecting words, which can be easily remembered through an acronym.

But they aren’t used much in professional writing as they suffer from few drawbacks.

They cover limited range of relationships

FANBOYS can cover limited range of relationships between two independent clauses. In practice, most use just and, but, and so (and, in fact, expresses a lame additive relationship, which I wouldn’t even count as a relationship). In other words, you’ll often struggle to come up with an appropriate coordinating conjunction for the relationship you want to express. I’ve seen this question many times: “What if I need to connect two independent sentences using a non-FANBOYS? None of the FANBOYS seem to fit here.”

They convey multiple key messages

Compound sentences give equal weight to each independent clause, implying at least two main messages in a sentence. Note that an independent clause(s) expresses the main idea of a sentence, with the dependent clause(s) chipping in with supporting or subordinate ideas.

One main idea per sentence is ideal for readers, which is achieved by complex sentences but not compound. Even compound-complex sentences, a cross between compound and complex sentences, find more favor in writing despite containing two independent clauses because most sentences need an odd dependent clause for some subordinate information.

What’s the implication of all this for your writing?

First, there is nothing wrong with compound sentences. Use them by all means, but use full range of complex sentences, especially those with relative and noun clause, and simple sentences, especially those with variety of phrases. Most don’t tap into their full potential.

Second, avoid more than two independent clauses in your compound sentences. Three main ideas in a sentence are too many.

Frequently Asked Questions

How many clauses are there in a compound sentence? Can a compound sentence have three independent clauses?

A compound sentence has at least two independent clauses, implying that it can have three, four, or any number of independent clauses. But, as discussed in the post, more than two independent clauses in a sentence make for poor writing.

Can a compound sentence not have a comma?

Yes. Every compound sentence doesn’t need a comma.

As discussed in the post, when a compound sentence comprises of two short independent clauses, we may omit comma. Second, compound sentences can be formed using semicolon and colon as well.

Can a compound sentence have a dependent clause?

Can a subordinating conjunction be used in a compound sentence?

Can a compound sentence have because in it?

No. A sentence containing a dependent clause or a subordinating conjunction can’t be a compound sentence. Since because introduces adverb clause, one of the three dependent clauses, it can’t be part of a compound sentence.

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