A complex sentence is a sentence with an independent clause and a dependent clause. It is one of the four main types of sentence structures. In a complex sentence, the independent clause shares the main information, and the dependent clause(s) provide details. Complex sentences let us share lots of information with just one sentence.
In the examples below, independent clauses are orange and dependent clauses are green .
As you can see, sometimes the independent clause comes first, and sometimes the dependent clause comes first.
All complex sentences have one independent clause and one or more dependent clauses. They often also include dependent “marker” words or coordinating conjunctions.
An independent clause is a clause that can exist as a sentence on its own. It has a subject and a predicate and makes sense as a complete sentence. As mentioned, the independent clause shares the main information of a complex sentence.
So, you can see that all of the clauses above are working sentences. All complex sentences have ONLY one independent clause.
A dependent clause has a subject and a predicate; BUT, it can’t be a sentence. It provides extra details about the independent clause, and it doesn’t make sense on its own, like these:
Though all of the examples above contain subjects and predicates, none of them make sense. Each leaves an unanswered question. By itself, a dependent clause is just a fragment (an incomplete sentence). So, it needs to be combined with an independent clause to be a sentence.
Complex sentences have at least one dependent clause, but they can have two or more.
A dependent marker word (also called a subordinating conjunction) goes at the beginning of an independent clause. It turns an independent clause into a dependent clause by adding details like time or context. Common dependent marker words include after, although, as, because, before, even if, even though, if, since, though, unless, until, whatever, when, whenever, whether, and while. Let’s start with an independent clause:
He was at the county fair = Independent clause
Now, add a dependent marker word, like “when”:
When he was at the county fair = Dependent clause
Here are some complex sentences with the marker words underlined:
Notice that when the sentence starts with a subordinating conjunction, there is a comma at the end of the dependent clause. When the subordinating conjunction is in the middle of the sentence, there is no comma.
This is different from what you’ve learned with compound sentences! So, remember when there is a subordinating conjunction in the middle of a sentence you don’t need a comma.
Complex sentences are very common and pretty easy to write, as long as you remember their rules. When writing a complex sentence, you should follow these important guidelines: