Complex Sentences  

Complex sentences are one of the four main sentence structures. They are made up of one independent clause (or main clause) and one or more dependent clauses (or subordinate clauses). The dependent clause is introduced and linked to the independent clause by a subordinating conjunction.

We use complex sentences to indicate a specific relationship between two ideas, and to clarify which of the two is more important. Consider the following example:

Although the reader can probably guess that the relationship between the two ideas above is one of cause and effect, that relationship could be specified by combining the two ideas into a complex sentence instead, as in:

By adding the subordinating conjunction “because,” we have transformed the previously independent clause “we were out of milk” into a dependent clause. It can no longer stand alone, but is dependent on the clause that it is now linked to. The relationship between the two ideas is now perfectly clear, and the importance of the independent clause “I went to the supermarket” is highlighted.

As mentioned, complex sentences are useful because they can indicate a very specific relationship between two ideas. Depending on what relationship we would like to indicate, we choose a specific subordinating conjunction. For example:

In the examples above, the subordinating conjunctions even if, while, and as long as introduce the dependent clauses and specify their relationship to the independent clauses.

Some of the most common subordinating conjunctions are:

Go to the chapter on Conjunctions to learn more about how subordinating conjunctions are used in complex sentences.

The order of the independent and dependent clause in a complex sentence is flexible. We can structure complex sentences with the independent clause first, as in:

The same sentences can be structured with the dependent clause first as well. This results in no change of meaning. For example:

Although there are exceptions, note that when the dependent clause is placed first, we generally follow it with a comma, as in the examples above. However, if the independent clause introduces the sentence, we usually do not need a comma.

While it’s a commonly quoted belief that a sentence should not begin with the word because, this is not an actual grammatical rule. Sentences can begin with because (and any other subordinating conjunction) as long as the sentence is not a fragment. For example

As the second sentence is a dependent clause without an independent clause to complete it, it is considered a fragment and must be corrected. However, the first sentence is a complete sentence because the dependent clause is followed by the independent clause “we decided to have a coffee.”