Adverb Clauses
Learn how an adverb clause describes a verb, the different categories of meaning it can express, and how it can sometimes be shortened.
Describing a verb
An adverb clause explains when, where, why, how, or under what condition.
An adverb clause is a dependent clause that functions as an adverb, describing a verb the same way a single adverb would.
In She left because she was tired., the clause because she was tired describes the verb left, explaining why the action happened. Compare this to She left immediately., where the single adverb immediately describes the same verb.
Adverb clauses fall into several categories of meaning, each introduced by its own set of subordinating conjunctions.
Before you begin
Adverb clauses are one of five clause types.
This lesson focuses on adverb clauses specifically. Clauses as a whole include four other types, each covered in its own lesson.
If you would like an overview of how clauses work in general, begin with the Clauses page.
The central idea
A clause can describe a verb the same way a single adverb does.
Compare a sentence with a single adverb to the same sentence with an adverb clause instead.
01
Single adverb
She left immediately.
02
Adverb clause
She left as soon as the meeting ended.
The useful question is: could a single adverb replace this clause?
Both immediately and as soon as the meeting ended describe when she left happened. If a clause can be swapped for a single adverb this way, it is functioning as an adverb clause.
Categories of adverb clause
Each category answers a different question about the main verb.
Time — when?
After the meeting ended, she left.
Common words: when, while, after, before, as soon as, until.
Reason — why?
She left because she was tired.
Common words: because, since, as.
Condition — under what circumstance?
If it rains, the event will move indoors.
Common words: if, unless, provided that.
Contrast — despite what?
Although it was raining, they went for a walk.
Common words: although, even though, while.
Place — where?
She waited where the bus usually stops.
Common words: where, wherever.
Position and punctuation
The same comma rule applies as with any dependent clause.
Adverb clause first: use a comma
Although it was raining, they went for a walk.
Adverb clause last: no comma is usually needed
They went for a walk although it was raining.
Shortening an adverb clause
Some adverb clauses can be reduced by dropping the subject and the verb be.
Full clause
While she was waiting, she read a book.
Reduced clause
While waiting, she read a book.
This shortened form is only possible when the subject of the adverb clause is the same as the subject of the main clause.
A useful decision guide
Ask what question the clause is answering about the verb.
01
Could a single adverb replace this clause?
If so, the clause is likely functioning as an adverb.
02
Does it answer when, why, under what condition, or where?
Match the category to the subordinating word being used.
03
Does the adverb clause come first, or last?
A comma follows it when it comes first; usually none is needed when it comes last.
04
Do the two clauses share the same subject?
If so, the adverb clause may be reduced by dropping the subject and the verb be.
Common mistakes
The punctuation and the choice of subordinating word both need attention.
A comma is needed when the adverb clause comes first.
Not: Although it was raining they went for a walk.
Correct: Although it was raining, they went for a walk.
Because is followed by a clause; because of is followed by a noun.
Not: She left because of she was tired.
Correct: She left because she was tired. / She left because of her tiredness.
Because introduces a clause with its own subject and verb; because of introduces a noun phrase instead.
A reduced clause needs matching subjects.
Unclear: While waiting, the bus arrived.
Clear: While she was waiting, the bus arrived.
Reducing the clause here would incorrectly suggest the bus itself was waiting, since the two clauses do not share the same subject.
Check your understanding
Which category does each adverb clause belong to?
Choose the correct answer for each sentence.
Unless the weather improves, the flight will be delayed.
✅ Exactly! Unless introduces a circumstance the outcome depends on.
❎ Not quite. Is this explaining a cause, or a circumstance the outcome depends on?
Look at the subordinating word that opens the clause.
Even though he was exhausted, he finished the race.
✅ Exactly! Even though signals a contrast between the two ideas.
❎ Not quite. Does this clause tell you when something happened, or set up an unexpected contrast?
Would you expect an exhausted person to finish the race?
Which sentence uses “because” correctly?
✅ Exactly! Because is followed by a full clause with its own subject and verb.
❎ Not quite. Because of is followed by a noun phrase, not a clause.
Does “she was tired” have its own subject and verb?
Choose the best explanation
Select the sentence that explains the adverb clause correctly.
Why is “She left because of she was tired.” not correctly formed?
✅ Exactly! Because of takes a noun phrase, while because takes a full clause.
❎ Not quite. Compare “because” and “because of” and what follows each one.
Why is “While waiting, the bus arrived.” unclear?
✅ Exactly! A reduced clause only works cleanly when both clauses share the same subject.
❎ Not quite. Think about who or what the reduced clause seems to describe.
Try it another way
Combine each pair of sentences using an adverb clause.
Use the subordinating word given.
The store closes. We need to buy milk. (use “before”)
✅ Exactly! The adverb clause comes first here, so a comma follows it.
❎ Not quite. Place “before” at the start of one clause, and remember the comma.
It started to rain. They cancelled the picnic. (use “because”)
✅ Exactly! The adverb clause comes last here, so no comma is needed.
❎ Not quite. Try placing “because” before the reason, at the end of the sentence.
Quick review
An adverb clause tells the reader when, why, where, or under what condition.
An adverb clause is a dependent clause that describes a verb, the same job a single adverb could do.
Categories include time, reason, condition, contrast and place, each with its own subordinating words.
A comma follows an adverb clause that opens the sentence; usually none is needed when it comes last.
A reduced adverb clause drops the subject and the verb be, but only when both clauses share the same subject.
Because is followed by a clause; because of is followed by a noun phrase.
Remember
Ask what question the clause is answering about the verb.
When, why, where, and under what condition are the questions an adverb clause answers. Identifying which one is being answered points you to the right subordinating word.