Complex Sentence

What Is a Complex Sentence?

A complex sentence is a sentence with one independent clause and at least one dependent clause. For example:
  • We must not swim where the seals are.
  • (The independent clause is highlighted. It is an independent clause because it could stand alone as a sentence. "where the seals are" is a dependent clause. It could not stand alone as a sentence.)
  • The monkeys move to the trees when the clouds darken.
  • (This is also a complex sentence. "When the clouds darken" is a dependent clause because it could not stand alone as a sentence.)

Table of Contents

  • Examples of Complex Sentences
  • Subordinating Conjunctions in Complex Sentences
  • Why Complex Sentences Are Important
  • Video Lesson
  • Test Time!
complex sentence
An independent clause (unlike a dependent clause) can stand alone as a sentence.

Examples of Complex Sentences

Below are examples of complex sentences. In each example, the independent clause is shaded. The dependent clause is unshaded.
  • Stay in the bath until the phone rings.
  • Both the cockroach and the bird would get along very well without us, although the cockroach would miss us most. (Joseph Wood Krutch, 1893-1970)
  • Leave while you can.
  • When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong. (Arthur C. Clarke)
  • (This is two complex sentences.)

Subordinating Conjunctions in Complex Sentences

The word used to link an independent clause to a dependent clause is called a subordinating conjunction. The most common subordinating conjunctions are although, because, before, even though, if, since, until, and when.
subordinating conjunction in a complex sentence
In these examples of complex sentences, the subordinating conjunctions are shown in bold.
  • We can never obtain peace in the outer world until we make peace with ourselves. (Dalai Lama)
  • Wise men speak because they have something to say. Fools speak because they have to say something. (Athenian philosopher Plato)
  • Even though he's a moron, I supported Tyson Fury. (Boxer David Haye)
The role of a subordinating conjunction and the dependent clause is to establish a time, a place, a reason, a condition, a concession, or a comparison for the main clause. (NB: Dependent clauses are also known as a subordinate clauses.) Read more about subordinating conjunctions.

The Four Types of Sentence Structure

A complex sentence is one of four main sentence structures, all of which are shown below. In these examples, the independent clauses are shaded.

A Complex Sentence

A complex sentence has an independent clause and at least one dependent clause. For example:
  • The human brain never stops working until you stand up to speak in public.

A Compound Sentence

A compound sentence has at least two independent clauses. For example:
  • I always wanted to be somebody, but I should have been more specific. (Jane Wagner)

A Simple Sentence

A simple sentence has just one independent clause. For example:
  • Curiosity killed the cat.

A Compound-Complex Sentence

A compound-complex sentence has at least two independent clauses and at least one dependent clause. For example:
  • I stopped believing in Santa Claus when he asked for my autograph in a department store, but I still want to believe in him.

Why Complex Sentences Are Important

There are two noteworthy issues related to complex sentences.

(Issue 1) Use a comma after a fronted adverbial.

Learning how to spot a complex sentence is useful because it helps with punctuating sentences correctly. In particular, it helps with deciding whether to use a comma with the dependent clause.

When your dependent clause is at the front and acts like an adverb – typically stating a time (e.g., When it's ready), a place (e.g., Where they live), or a condition (e.g., If you were in my shoes) – then it is usual to use a comma after the dependent clause to show where the independent clause starts. When such a clause appears at the back of your sentence, it is usually not offset with a comma. In these examples, the independent clauses are shaded.
  • I became a people-watcher when I lost all my friends. (Singer Taylor Swift)
  • When I lost all my friends, I became a people-watcher.
  • If it is, it is. If it's not, it's not. (Singer Ziggy Marley)
  • It is if it is. It's not if it's not.
So, the guidance is as follows:
  • When your adverbial is at the front, use a comma.
  • Don't use a comma when your adverbial is at the back.

(Issue 2) Uh oh, there's more to Issue 1.

Unfortunately, there is a little more to Issue 1 than stated. The comma really determines whether the clause is restrictive or non-restrictive. However, the simple rule given at Issue 1 will satisfy 99% of situations. Read more about using commas with independent and dependent clauses (see Points 3 and 4).
Read more about adverbial phrases and adverbial clauses.

Learning the other sentence structures will also help with punctuating sentences correctly.

Video Lesson

Here is a short video explaining what we mean by complex sentence. video lesson

Are you a visual learner? Do you prefer video to text? Here is a list of all our grammar videos.

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This page was written by Craig Shrives.