What is a Complex Sentence? Definition and Examples

A complex sentence has one dependent clause and another independent clause. But how do you identify or write this sentence type?

Find out what a complex sentence is and some examples of this sentence structure. I’ll also show you how to identify a complex sentence to help you become a stronger writer. 

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Complex Sentence Definition

They are one of the four types of sentences according to structure. These complete sentences contain one independent clause and at least one dependent or subordinate clause.

Let’s have a quick refresher on clauses.

Dependent clauses or subordinating clauses cannot function as a standalone sentence. Despite their understandable ideas, they are only fragments or phrases.

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Example: Because I’m happy.

Independent clauses are a type of clause that can stand on their own as a sentence. These entire ideas have a subject and predicate. 

Example: I’m happy. 

Complex Sentence Examples 

  • Lotus is a symbol of fertility because it’s related to the goddess Isis.
  • It’s a bad idea to spoil conceited people unless they develop empathy.
  • You can’t leave the school until you finish your assignment.
  • The poor person was texting when he dropped his food.
  • After Jane drank the milk, she got a stomach ache. 

What is a Conditional Sentence?

These are one of the most common types of complex sentences that discuss hypothetical scenarios. These categories often have an if-and-then logic. Here are some examples:

  • If today is Thursday, tomorrow is Friday.
  • You can’t go to bed unless you’ve brushed your teeth.
  • Download a grammar checker if you need help with confusing compound sentences. 

How to Identify a Complex Sentence

The simple rule to identify a complex sentence is to know the difference between an independent and dependent clause. You already know that an independent clause can function as a complete sentence while a dependent sentence can’t.

But they can still be confusing because both types of clauses have a subject and a verb. 

Examples:

  • Dependent clause: Since I left the lights on (subject: I, predicate: left).
  • Independent clause: I left the lights on (subject: I, predicate: left).

The secret is to look for subordinating conjunctions. A dependent clause always has subordinating conjunctions like because, until, even though, and in case. 

Examples:

  • Dependent clause: Even though it’s raining (What will happen even though it’s raining?)
  • Independent clause: It’s raining. (Despite being short, this declarative sentence states the whole idea that it’s raining.) 

There are several subordinating conjunctions. But as long as it’s not any of these conjunctions, then it is a subordinating conjunction:

  • For.
  • And.
  • Nor.
  • But.
  • Or.
  • Yet.
  • So.

Examples:

  • Independent clause: And he took me home.
  • Dependent clause: Until he took me home.

Note that a subordinate or dependent clause describes another clause. In a complex sentence, the dependent clause describes the independent clause. 

Examples: We talked all day until he took me home. (In this sentence, the dependent clause “until he took me home” is an adverbial clause. It describes the action of “talking.”)

Also, a dependent clause should have an independent clause to be a complete sentence. So, if you find a pair of these clauses, that’s automatically a complex statement.

Example: We talked all day until he took me home. (“We talked all day” is the independent clause, and “until he took me home” is the dependent clause.)

The other types of sentence structures in writing are compound sentence, compound-complex sentence or complex-compound sentence, and simple sentence.

Simple vs. Complex Sentences

The biggest difference is the clauses they contain. 

What Does a Complex Sentence Contain?

It has only one independent clause, and that’s it. So, if you see a statement with two clauses, they cannot be simple sentences. 

Example: Her mom is a fighter. She battled cancer for four years. 

In the statement above, two simple sentences show complete thoughts. These are:

  • Her mom is a fighter.
  • She battled cancer for four years.

Forming a Complex Sentence

These have simple grammar rules. You can quickly remember these guidelines as long as you know the difference between a dependent and independent clause.

Include a Conjunction

Another rule when forming a complex sentence is always to include subordinating or complex conjunctions to link the dependent and independent clauses. A subordinating conjunction has either of the following functions:

  • Expresses relationships between place, time, or change.
  • Shows cause and effect.
  • Modifies or adds details to the independent clause.

Here are some common subordinating conjunctions or complex sentence conjunctions: 

  • After.
  • Although.
  • Because.
  • Before.
  • If.
  • Since.
  • Though.
  • Unless.
  • Whenever.
  • Wherever.
  • While.

Some people call subordinating conjunctions “heart words” because they transform two statements into one concise thought. Even if both have their own subjects and verbs, they can be joined together through these heart words. 

Proper Comma Usage

The comma function is essential to put a pause in the middle of the statement. But despite the multiple times commas are essential, you shouldn’t use them if the dependent clause is the second clause. Here’s an example:

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I cried, because I was happy.

You don’t need a comma in the statement above because the second clause, “because I was happy,” is dependent. Instead, you can say:

  • I cried because I was happy.
  • Because I was happy, I cried.

The second sentence above shows that you can use a comma if the complex sentence starts with the subordinate clause. 

Learn how to use a comma after a fronted adverbial in your complex sentence. When the dependent clause is in front and serves as an adverb of time, place, or condition, it is acceptable to use a comma. Here are more examples:

  • If I were in their shoes, I would do the opposite. (The fronted adverbial, which is also a dependent clause, shows a condition.)
  • Once the food is prepared, the staff will call your name. (The adverb clause shows time.)

How to Form a Complex Sentence With an Adjective Clause

An adjective clause is one of the three types of clauses that function as dependent clauses. This type of clause modifies a word or a group of words in another clause of a sentence. These clauses use subordinate conjunctions that, who, which, and whom. Here’s an example:

He’s the teacher who gave me good grades.

“He’s the teacher” is the independent clause, while “who gave me good grades” is the dependent clause. The dependent clause modifies the noun “teacher.”

Forming a Complex Sentence with an Adverbial Clause

Adverbial clauses can start with conjunctions when, as, before, because, since, if, etc. These clauses modify an action, adjective, or another adverb in the sentence. Here’s an example:

I could not attend as I am ill.

This adverbial clause is a cause clause, with the dependent clause “as I am ill” modifying “could (not) attend.”

How to Form a Complex Sentence with a Noun Clause

Noun clauses are the last type of complex sentence clauses that function as one dependent clause. Here are some examples:

  • Whatever was added to that chicken was perfect.
  • Whoever made this spreadsheet deserves a raise.

Tips When Writing Complex Sentences

Remember the following tips when forming complex statements using dependent and independent clauses in writing.

Don’t Lose Sight of Your Main Idea

Punctuations and a comma combination can result in ever-longer statements. Even if your single sentence structure follows grammar rules, your primary thoughts may be unclear to your reader.

Avoid Run-On Sentences

A run-on sentence occurs when the writer does not correctly connect two clauses in a complex statement. This writing error is the equivalent of the comma splice error in the compound and compound-complex sentences.

Don’t forget the rules on commas and subordinating conjunctions so you can avoid these mistakes.

Don’t Confuse Compound Sentences with Complex Sentences

Complex sentences share similarities with compound sentences, so don’t feel bad for mixing them up. Compound ones are a single sentence that contains two or more independent clauses. 

Meanwhile, complex sentences are one of the types of sentences with an independent and a dependent clause.

The main tip for differentiating between the varied sentence structures is to check the conjunction. If it uses coordinating conjunctions (FANBOYS), it’s a compound sentence.

Write Complex Sentences Properly

Learning the basic sentence structures will help you practice variety in your writing. Overusing one style of sentence can make you sound monotonous and boring.  

One of the four basic sentence types is the complex sentence, which contains one dependent and one independent clause.

Remember these writing strategies when writing complex sentences:

  • Use subordinating conjunction.
  • Only add a comma when the subordinate or dependent clause comes first.
  • Don’t lose sight of your main idea.