What is a Complex Sentence?
A complex sentence is a sentence that contains an independent clause and one or more dependent clauses. An independent clause can stand alone as a sentence, but a dependent clause even though it has a subject and a verb cannot stand alone.
Here are some examples of complex sentences. The independent clause is in bold;
Complex Sentences Explained
As you may have noticed from the examples above, a complex sentence can either start with the independent clause or the subordinate clause. If the subordinate clause comes first, you must add a comma. This is not needed if the independent clause comes first.
The football match was cancelled.
A subordinate clause cannot stand alone, it needs to be linked to the independent clause to make sense.
Because it was raining.
Put the two together and you have a complex sentence. Often the sentence will make sense whether the independent clause or the subordinate clause is put first;
Because it was raining, the football match was cancelled.
The football match was cancelled, because it was raining.
The difference between a compound sentence and a complex sentence.
Everyone can get confused between a compound sentence and a complex sentence, so here's an easy explanation:
A compound sentence has two independent clauses. Each of these clauses is equally important, they are joined by a co-ordinating conjunction that does not change the rank of either clause. For example;
He sang and she danced.
Subject / verb / co-ordinating conjunction / subject / verb.
There are seven coordinating conjunctions that enable two clauses to be equal and they are worth taking the time to memorise;
A complex sentence has one independent clause and at least one dependent clause. This means that the clauses are not equal, they use a co-ordinating conjunction that changes the rank of one or more of the clauses to make it less equal. For example;
My Dad laughed when I told a joke.
Independent clause / subordinating conjunction / dependent clause
If we took away the 'when', we would have two equal clauses; ‘My Dad laughed’ and ‘I told a joke.’ The use of the conjunction 'when' connects the clauses but displays a complex relationship between the two; indicating which is dominant and which is subordinate. Thus, a complex sentence.
There are lots of subordinating conjunctions (too many to memorise in fact!), but here are a few common examples;
The BBC has a great factsheet and game on complex sentences: