A clause is a group of words that contains a subject and a verb. Some clauses are dependent: they can't stand alone and need an independent clause, or sentence, to support them.

These dependent clauses can be used in three ways: as adjectives, as adverbs and as nouns. This article focuses on adverb clauses.

What is an adverb clause?

An adverb clause is a dependent clause that acts as an adverb. That is, it modifies the verb in a sentence in the same way an adverb does:

• Then the puck flew past the goalie into the net.
  (adverb of time, modifying flew)
• When Joe hit the puck, it flew past the goalie into the net.
  (adverb clause of time, modifying flew)

What words are signs of an adverb clause?

Adverb clauses begin with subordinating conjunctions. The most common conjunctions used in adverb clauses are listed below, according to the type of clause they introduce:

• Cause: as, because, since
  Since the rain washed out the bridge, we'll have to cross on foot.
• Comparison: a s…as, than
  John sings better than I do.
• Condition: if, provided that, unless, whether
  I'll go to the barbecue if you can give me a lift home.
• Concession: although, even though, whereas, while
  Even though Eric arrived late, he still got a seat.
• Manner: as, as if, as though
  Kristen looked as if she would explode.
• Place: where, wherever
  Take this map with you wherever you go.
• Purpose: in order that, so that
  Natalia closed the gate so that the llama would not stray.
• Time: after, as, before, once, since, till, until, when, while
  Until Al called, I expected to spend the evening at home.

When does an adverb clause need commas?

The use of commas with an adverb clause depends on the position of the clause and its degree of importance.

When placed before the independent clause, an adverb clause takes a comma after it:

• When I hear the song "Spanish Eyes, " I always feel like dancing.

When placed in the middle of the independent clause, an adverb clause generally acts as an interrupter and requires a pair of commas (one before and one after):

• My cousin, because she enjoys travelling, goes on a cruise every winter.

When placed after the independent clause, an adverb clause may or may not require a comma, depending on whether it is essential to the meaning of the sentence.

Essential clauses don't take commas:

• The package came after you left.

Here, the adverb clause after you left identifies the time the package was delivered, so it is essential to the meaning of the sentence. For that reason, it must remain closely attached to the independent clause and is not set apart by a comma.

Note that clauses introduced by until and the conjunctions of comparison than and as…as are always essential:

• They took shelter in the cave until the storm ended.
• Jorge is taller than Greg (is).
• No one can play that sonata as skillfully as Marsha (does).

Non-essential clauses need commas:

• The package came at 8:30, after you left.

Here, the phrase at 8:30 identifies the time the package was delivered. The adverb clause after you left is merely additional information that is useful but not essential. Therefore, the clause is set off by a comma.

Note that clauses beginning with although, even though, though and whereas are always non-essential:

• Lisa won the prize, even though (although, though) the competition was stiff.
• Cara wanted to paint the room blue, whereas Paul preferred green.