Comma in Complex Sentences

A complex sentence is made up of an independent clause (complete sentence) and one or more dependent clauses connected to it. A dependent clause (a part sentence) lacks one of the elements that would make it a complete sentence.

The following are examples of dependent clauses:

• since Mariam and Sarimah left the office before noon
• while he waited at the train station
• after they left on the bus

Dependent clauses such as those above cannot stand alone as a sentence, but they can be added to an independent clause (complete sentence) to form a complex sentence.

Dependent clauses begin with subordinating conjunctions. Below are some of the most common subordinating conjunctions:

• after
• although
• as
• because
• before
• even though
• if
• since
• though
• unless
• until
• when
• whenever
• whereas
• wherever
• while

A complex sentence joins an independent clause with one or more dependent clauses.

The dependent clauses can go first in the sentence, followed by the independent clause, as in the following:

• Since Mariam and Sarimah left the office before noon, I did not see them there.
• While he waited at the train station, Johan realized that the train was late.
• After they left on the bus, Mariam and Sarimah realized that Johan was waiting at the train station.

Tip: When the dependent clause comes first, a comma should be used to separate the two clauses. 

Conversely, the independent clauses can go first in the sentence, followed by the dependent clause, as in the following:

• I did not see them at the office because Mariam and Sarimah left the office before noon.
• Johan realized that the train was late while he waited at the train station.
• Mariam and Sarimah realized that Johan was waiting at the train station after they left on the bus.

Tip: When the independent clause comes first, a comma should not be used to separate the two clauses.

The term periodic sentence is used to refer to a complex sentence beginning with a dependent clause and ending with an independent clause, as in "While he waited at the train station, Johan realized that the train was late."

Periodic sentences can be especially effective because the completed thought occurs at the end of it, so the first part of the sentence can build up to the meaning that comes at the end.