Sentences in North American academic English have at least one subject and at least one verb (as in "Peacocks are loud"). A complex sentence is a type of sentence contains at least one dependent clause that cannot stand alone as a simple sentence (it is not a complete idea on its own). For example, "Because they are loud" is a dependent clause in the sentence below:
- Because they are loud, I can hear the peacocks before I see them.
By contrast, an independent clause like "I can hear the peacocks before I see them" makes sense on its own. Similar to "because", clauses starting with "if", "since", "because", "when", "as", "although", "while", "until" , "after", and "before" do not express a complete idea and cannot stand alone as a simple sentence. Instead, these clauses provide information about time, place, cause or effect either at the beginning or at the end of a sentence, as in:
- The sun rose before she woke up.
- After they finished eating, they went home.
- We cannot leave until he joins us.
Words like "before", "after", and "until" are sometimes called dependent markers, or subordinating conjunctions. When they start a sentence, they are followed by a comma and a complete idea in North American academic English (as in this sentence).
For a complete list of subordinating conjunctions in dependent clauses, see The Subordinate Clause and for more information on how punctuate complex sentences, see Comma Usage in Compound and Complex Sentences.
To learn more about the basic elements of a sentence, see Sentences and Style and to see examples of other sentence types, see What is a Simple Sentence?, What is a Compound Sentence?, and What is an Independent or a Dependent Clause?
