Complex Sentences Show
Relationships between Ideas.

Both compound and complex sentences combine two clauses (each a potential sentence with a subject and predicate) into one sentence. Complex sentences contain two unequal clauses. We use them to show more complicated relationships between two ideas.

family silhouette with a complex sentence about family size.a complex sentence on family size. (Compare it to the picture text on Compound Sentences.)
family silhouette with a complex sentence about family size.a complex sentence on family size. (Compare it to the picture text on Compound Sentences.)

Imagine that a friend asks you, “Did you see the odd-looking woman at the bank?”

You might answer, "I saw a woman. She was wearing a huge straw hat and a green and pink striped dress with black and white striped socks...” However, it would sound better (less repetitive) to say, “I saw a woman who was wearing a huge straw hat (etc.)”

By converting two sentences into one complex sentence this way, we can vary sentence length and structure. (Sentences of different lengths are more interesting to listen to than sentences that all sound the same). We can also show the relationship between ideas more clearly.

Types of Complex Sentences

There are three kinds of complex sentences. The dependent clause can act as a noun, an adjective modifying a noun in the main (independent) clause, or an adverb modifying the main clause’s verb or the whole main clause.

Although a dependent clause contains both subject and verb (predicate), it cannot serve as a sentence by itself.

The preceding sentence serves as an example.

The dependent clause begins with ‘although,’ and modifies (gives more information about) the independent clause that follows it.

Although a dependent clause contains both subject and verb” is not a complete sentence but a fragment. It doesn’t express a complete thought. (Anyone listening would wait to hear the end of the thought. They would wonder, 'What is the speaker's point?')

Noun and adjective clauses

Noun and adjective clauses often begin with ‘if, ‘that,’ or ‘wh’ words: who, what, when, where, why, which, whom, whose, whoever, whatever, whenever, wherever, etc. (Sometimes ‘who’ and ‘which’ can serve as the subject of a clause since they are pronouns. ‘That’ is often omitted.)

(Clauses acting as adjectives are often called 'relative clauses.' They are often used to help define the noun in the main clause, to give extra information about it, or specify which person or thing is meant by it. See examples 3-5 below for each of thse uses.) 

Some examples (with the dependent clause in italics):

  1. I know that he is untrustworthy. He lies whenever the truth is inconvenient. (or: Whenever the truth is inconvenient, he lies.)
  2. I think (that) Joe would be the best for the job.
  3. Steamships, which are large boats powered by steam engines, ended the 'Age of Sail.'  (The dependent clause here defines what a steamship is.)
  4. His father, who was otherwise very smart,  never figured out how to use email.
  5. Do you see the man who is carrying a black briefcase? (The dependent clause specifies which man,)

Adverb Clauses

Subordinating conjunctions begin an adverb clause and show its relationship to the independent clause.

They can show:

  • time or place relationships (before, after, once, until, as long as, as soon as, when, whenever, where, wherever, while),
  • comparison (as much as)
  • contrast (although, though, even though, unless, than, rather than),
  • conditions on the relationship (if, as if, even if, unless, provided) or
  • cause and effect (as, since, because, in order that, now that, so that, whether, why.)

Some examples (with the dependent clause in italics):

  1. Before I taught English, I worked in a library. (or: I worked in a library before I taught English.)
  2. Some students listen to music while they study.
  3. Although he finished the book, he still needs to study his notes on it.
  4. Students in California cannot graduate from high school unless they pass the CAHSEE (exit exam.)
  5. “I wouldn’t marry you even if you were the last man on earth!”
  6. If you had a million dollars, what would you do with it?
  7. “Try to act as if you were a civilized human being.” (This is sarcastic advice; don’t use it on a friend!)
  8. Their corn crop failed because there was a drought.
  9. Now that Tim’s an adult, his parents expect him to pay rent. They think (that) he should contribute to the household income while he’s living at home. (There are two dependent clauses in the second sentence.)
  10. Is it fair to charge fees for services whether students use them or not?

Notice that either the dependent or the independent clause can begin the sentence (they’re reversible), but if the dependent clause is first, it is followed by a comma.

Many subordinating conjunctions can also serve as other parts of speech (prepositions like after the party, etc.)

Note that ‘because of’ is a preposition. It should be followed by a noun phrase.

‘Because’ is a conjunction and must be followed by a clause with both subject and verb.

These are both correct:

  • Ken stayed home because of his cold.
  • Ken stayed home because he had a cold.

However, it is not correct to say

  • Ken stayed home because of he had a cold.
  • ·Ken stayed home because his cold. (An English speaker would think ‘because his cold what?’ ‘because his cold got worse?’ ‘because his cold made him tired? We expect to hear a complete thought after because.)

Complex sentences are not difficult to understand if you recognize the meaning of each conjunction and clause. Because they are very common, especially in academic writing, they are worth analyzing and mastering.

You can practice complex sentences at Adverb Clause and Complex Sentence Practice. For comparison, see also Compound Sentences, which discusses linking two more-or-less equal, independent clauses.

HomeEnglish Grammar Lessons> Complex Sentences.

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