Commas After Introductory Clauses

Place a comma after an introductory adverb clause.

An adverb clause shows time, place, degree, extent, cause, or condition. It is a subordinate clause which begins with a subordinating conjunction.

Correct: Before the curtain fell, the actors bowed.

Correct: If the next two nights are sellouts, the play will be extended.

Note that if a sentence ends with an adverb clause, no comma is used. The subordinating conjunction is enough of a separation.

Incorrect: The play's run will be extended, if the next two nights are sellouts.
(No comma needed with adverb clause at end of sentence.)

Correct: The play's run will be extended if the next two nights are sellouts.

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