An adverbial clause is a subordinate clause which takes the place of an adverb in a sentence.
Just like adverbs and adverbial phrases, adverbial clauses answer the questions where, when, how, to what extent, with what goal/result and under what conditions.
In addition, an adverbial clause may tell why.
Note how an adverb clause can replace an adverb and an adverbial phrase in the following Example:
Adverb: The Prime Minister gave a speech here.
Adverbial phrase: The Prime Minister gave a speech in the afternoon.
Adverbial clause: The Prime Minister gave a speech where the workers were striking.
Usually, an adverbial clause is introduced by a subordinating conjunction like because, when, whenever, where, wherever, since, after and so that.
Note that a subordinate adverb clause can never stand alone as a complete sentence.
After they left dining hall the above adverbial clause will leave the reader asking what happened after they left the dining hall?
Adverbial clauses express relationships of cause, effect, place, time and condition.
Adverb clauses of cause answer the question why?
Ngozi wanted to kill her uncle because he had murdered his father.
Adverbial clauses of effect answer the question with what goal/result?
Example: Ngozi wanted to kill her uncle so that his father’s murder would be avenged.
Time Adverbial clauses of time answer the question when?
Example: After Ngozi’s uncle married her mother, she wanted to kill him Condition Adverbial clauses of condition answer the question under what conditions?
Example: If the uncle cooperates, Ngpzi may decide to pardon him.
Place Adverbial clauses of place answer the question where?
Example: Ngozi organized a demonstration where his father’s murder occurred.
Note that an adverbial clause can appear either before or after the main clause of the sentence.