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.)

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. 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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