What is a Complex Sentence and How to Write One?

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 complex sentence.

Learn the other three types:

What is a complex sentence?

A complex sentence is a sentence that contains one independent clause and at least one dependent clause. So, a complex sentence can have two dependent clauses but not two independent clauses.

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

Note: Feel free to use the above and other images in the post, using the link (url) of this post for reference/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).

The difference between these sentences though extends beyond just the number of dependent and independent clauses. Learn more subtle differences between compound and complex sentence:

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

Mary won the sprint. [Independent clause]

If we add a dependent clause to it, we get a complex sentence.

Mary won the sprint, even though she was not quick off the blocks. [Independent clause + Dependent clause = Complex sentence]

We can add another dependent clause, and the sentence will remain a complex sentence.

Mary, who has been training hard for the last three months, won the sprint, even though she was not quick off the blocks. [Independent clause + Dependent clause + Dependent clause = Complex sentence]

You can add more dependent clauses, but the sentence will remain a complex sentence. Remember, there is no restriction on the number of dependent clauses in a complex sentence.

But none of these are complex sentences because they don’t contain one independent clause and at least one dependent clause.

Mary won the sprint. [Independent clause]

Mary won the sprint, but there was little time to celebrate. [Independent clause + Independent clause]

Mary won the sprint, but there was little time to celebrate as another event was awaiting her. [Independent clause + Independent clause + Dependent clause]

While there is just one type of independent clause, there are three types of dependent clauses: noun clause, relative clause (also called adjective clause), and adverb clause. Many think that dependent clauses in a complex sentence can be an adverb clause only (the clauses starting with because, although, since, while, etc.), but that’s not true. Any of the three or a mix of the three can make a sentence complex.

Here is how you can write complex sentences with each of the three dependent clauses.

1. How to write a complex sentence with noun clause?

A noun clause is a dependent clause that can take the place of a noun in a sentence. Put simply, it can do whatever a noun (or pronoun) can do in a sentence: subject, object of verb, indirect object of verb, object of preposition, and subject complement.

What earlier committee recommended shouldn’t influence the current committee’s recommendations. [Noun clause as subject]

I know when I should ask questions. [Noun clause as object of verb]

He spoke at length on how he makes money on YouTube. [Noun clause as object of preposition]

Our problem is whom we trust. [Noun clause as subject complement]

1.1 These are not complex sentences though

These sentences though are not complex because they no longer have a dependent clause. The underlined parts now don’t have both subject and verb; hence they’re just phrases. (Compare them with the earlier sentences.)

Earlier committee’s recommendations shouldn’t influence the current committee’s recommendations.

I know when to ask questions. [Here, to ask is a non-finite (infinitive) form of verb]

He spoke at length on how to make money on YouTube. [Here, to make is a non-finite (infinitive) form of verb]

The three sentences contain an independent clause each, implying they’re simple sentences.

More resources:

1.2 Punctuation

Because a noun clause simply takes the place of a noun or pronoun, it doesn’t require any additional punctuation – comma or dash – as is the case with other two dependent clauses. If a noun or pronoun in its place doesn’t require a comma, a noun clause too won’t. This sentence, for example, is incorrectly punctuated because a noun or pronoun in its place won’t require a comma.

What he said in his speech today, is unbelievable. [Incorrect punctuation as That, is unbelievable would also be incorrect.]

More on joining a noun clause to an independent clause:

2. How to write a complex sentence with relative clause?

Also known as adjective clause, a relative clause is a dependent clause that describes a noun or pronoun, just like an adjective does, and is placed immediately after the word or phrase being described.

The damage that negative media coverage has done to our brand will be tough to repair.

I care for my old friends, who’ve stood by me in thick and thin.

Isabella, who speaks four languages fluently, prefers to speak in Spanish.

2.1 These are not complex sentences though

These aren’t complex sentences because they no longer contain a dependent clause. The underlined groups of words are phrases – and not clauses: They no longer contain both subject and verb. Compare them with the earlier sentences.

The damage done to our brand by negative media coverage will be tough to repair.

Isabella, a fluent speaker of four languages, prefers to speak in Spanish.

The two sentences contain just an independent clause, implying they’re simple sentences.

2.2 Punctuation

When a relative clause is essential to the meaning of the noun being described, it carries no comma. In the first sentence, without the relative clause, we wouldn’t know which damage will be tough to repair. Hence, it’s essential and doesn’t take any commas.

However, when a relative clause is not essential to the meaning of the noun being described, it is set off by a pair of commas. In the second and third sentences, even without the relative clause, we would know who my old friends and Isabella are. Hence, the two relative clauses are non-essential and would take a pair of commas. The second takes only one comma because the second comma is merged with the period.

More on joining a relative clause to an independent clause:

3. How to write a complex sentence with adverb clause?

An adverb clause is a dependent clause that acts as an adverb in a sentence, implying that it answers important questions to provide necessary background information in a sentence. In common parlance, adverb clauses express variety of relationships in sentences: relationship of reason through clause starting with because and since, relationship of contrast through clause starting with although and even though, and so on. Most of us, in fact, write majority of our complex sentences with adverb clause, but it’s not the most popular dependent clause in complex sentences for professional writers. Examples:

Although Mary was slow off the blocks, she won the sprint.

After Mary finished the race, she rushed to another event.

I couldn’t participate in the sprint because I picked up an injury at the last moment.

I climbed down from my position before the friendly argument could heat up.

Unlike the other two dependent clauses, adverb clauses are usually mobile in a sentence. You can move the adverb clause in the above sentences to the back or front without affecting meaning or grammatical sanctity.

3.1 These are not complex sentences though

Have a look at these sentences and tell why these aren’t complex.

Although slow off the blocks, Mary won the sprint.

After finishing the race, Mary rushed to another event.

I couldn’t participate in the sprint because of an injury at the last moment.

That’s because none of the underlined parts are dependent clauses. The underlined parts no longer contain both subject and verb and hence are phrases. (Compare them with the earlier sentences.) In the third sentence, because of is in fact a preposition, which is often confused with the subordinating conjunction because. All three sentences contain an independent clause each, implying they’re simple sentences.

3.2 Punctuation

1. When an adverb clause begins a sentence, a comma is always used to separate it from the independent clause.

While he made coffee, I listened to music.

Because I get a chance to meet interesting people, I love to travel.

2. When an independent clause begins a sentence, a comma is rarely used to separate it from the adverb clause.

I listened to music while he made coffee.

I love to travel because I get a chance to meet interesting people.

I’ve rarely seen students getting the first rule wrong, but errors are common here. Some use comma even in this position, and some use it inconsistently.

The second rule though has few exceptions where comma is acceptable.

3. When an independent clause begins a sentence, comma is acceptable where the adverb clause expresses contrast with the independent clause. Such contrast is often expressed by subordinating conjunctions although and even though.

I met with an accident, although I was driving at only 40 kph.

Mary won the 100-meter dash in her personal best time, even though she was not quick off the blocks.

Some publications though follow their own style rules and use a comma even without contrast. So, don’t scratch your head if you see a sentence like this.

I love to travel, because I get a chance to meet interesting people.

But if you do the same, it might be taken as an error.

More on joining an adverb clause to an independent clause:

So far, we looked at one dependent clause per sentence, but in practice multiple dependent clauses, often of more than one type, appear in sentences. Here are few examples, with the type of dependent clause mentioned in the same order next to the sentence.

Complex sentences with multiple dependent clauses

If you live in a glass house, don’t throw stones because others too may throw stones at you which may shatter your glass house. [Adverb clause/ Adverb clause/ Relative clause]

If friends meet too often or if they intrude into each other’s lives, friendship may weaken. [Adverb clause/ Adverb clause]

What you plan to do is completely insane because you’re not prepared for it. [Noun clause/ Adverb clause]

I don’t like calling up Tom any longer for regular chitchats after he failed to return the money I lent three months back. [Adverb clause/ Relative clause. The adverb clause contains the relative clause I lent three months back.]

See more examples of complex sentences:

Exercise

Depending on the relationship between the two independent clauses in each question, convert one of them into a dependent clause. It could be a noun, a relative, or an adverb clause.

1. I didn’t do well in the exam. I was down with fever for the last three days.

2. He said something in his speech today. It is unbelievable.

3. Hannah is attending Brown University. It was her first choice.

4. The police arrested the man. The man raised false alarm of a bomb on the plane.

5. Online commerce boomed during the pandemic. Most industries showed precipitous decline in sales.

Answers to Exercise

1. I didn’t do well in the exam because I was down with fever for the last three days. [Adverb clause]

2. What he said in his speech today is unbelievable. [Noun clause]

3. Hannah is attending Brown University, which was her first choice. [Relative clause]

Hannah is attending Brown University as it was her first choice. [Adverb clause]

In the first sentence, the relative clause merely adds extra information about Brown University. In the second, the adverb clause articulates the reason for attending Brown University.

4. The police arrested the man who raised false alarm of a bomb on the plane. [Relative clause]

5. Although online commerce boomed during the pandemic, most industries showed precipitous decline in sales. [Adverb clause]

How to identify a complex sentence?

Identifying a complex sentence is all about identifying an independent clause and at least one dependent clause in the sentence. That’s not straightforward though. Try identifying the type of these sentences.

He was admired in the business community but was admired most for his work with children no one cared for.

Farm sector will be hard hit in future because of change in weather patterns, a direct result of climate change.

The first is a complex sentence as it contains an independent clause and a dependent clause (no one cared for). The second is a simple sentence, containing one independent clause. There often are false positives and false negatives in identifying clauses.

Identifying dependent and independent clauses is a task in itself and can’t be covered in the limited space here.

Get better at identifying clauses in a sentence:

What implications do complex sentences hold for your writing?

Why learn complex sentences?

Complex sentences join multiple subordinate ideas (represented by dependent clauses) to a main idea (represented by an independent clause), expressing wide range of relationships between them while adding variety to your writing.

Most kids graduate from writing one-clause sentences to multi-clause sentences by combining independent clauses through and and then. Gradually, they expand their repertoire and start using multiple clauses – dependent and independent – through coordinating conjunctions beyond and; adverb clauses starting with subordinating conjunctions such as because, since, while, after, and although; and few noun clauses that are common in speaking.

But you can do better.

You may be a fan of compound sentences because of their simplicity, but, compared to complex sentences, they’re much less used in professional writing. Complex sentences represent one main idea (because they’ve one independent clause) and are quite flexible in absorbing multiple dependent clauses as Lego-like parts.

So, if you can expand your repertoire of complex sentences by including relative and noun clauses, you’ll lift your writing significantly. (As we saw in this post, there is more to complex sentences than just adverb clause.)

Frequently Asked Questions

Can a complex sentence have two independent clauses?

No.

While a complex sentence can have more than one dependent clause, it can have one and only one independent clause. The moment you add a second independent clause, the sentence becomes a compound-complex sentence.

Can a complex sentence have two dependent clauses?

Yes.

A complex sentence contains exactly one independent clause and at least one dependent clause, which means it can have one, two, or more dependent clauses.

Can a complex sentence have a semicolon?

No. Semicolon, if you recall, is used most commonly to separate two independent clauses. The very fact that a semicolon comes with two independent clauses means that a complex sentence can’t have a semicolon.

However, a complex sentence can contain a semicolon if semicolon is used as a super-comma, its second popular use. For example:

The President, who has been of late under fire for rising crime, stopped at Paris, France; Copenhagen, Denmark; Oslo, Norway; and Barcelona, Spain during his recent European tour.

This use of semicolon though isn’t common.

Can a complex sentence have a coordinating conjunction?

Yes, if the coordinating conjunction is used to join words or phrases. No, if the coordinating conjunction is used to join clauses because it can join only independent clauses, and, by definition, a complex sentence can’t have more than one independent clause.

Can a complex sentence be a question?

Yes. Examples:

How can you do whatever you want to? [Noun clause]

How can John, who was penalized for over-speeding just last month, be so stupid to again get caught for the same offence? [Relative clause]

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