Complex Sentence with Introductory Clause

A complex sentence is made up of an independent clause and a dependent clause. If the dependent clause comes first, it needs a comma to separate it from the rest of the sentence. (The dependent clause is introduced by a subordinating conjunction. Some of the most common subordinating conjunctions are after, although, because, before, if, since, when.) The pattern looks like this:

Note: If the sentence begins with the independent clause and ends with the dependent clause, do not use a comma.