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 noun clauses.
A noun clause is a dependent clause that acts as a noun.
Noun clauses most often begin with the subordinating conjunction that. Other words that may begin a noun clause are if, how, what, whatever, when, where, whether, which, who, whoever, whom and why.
Since a noun clause acts as a noun, it can do anything that a noun can do. A noun clause can be a subject, a direct object, an indirect object, an object of a preposition, a subject complement, an object complement or an appositive.
Examples:
Whatever you decide is fine with me.
(subject of the verb is)
With your bouncy personality, I knew that you'd enjoy bungee jumping.
(direct object of the verb knew)
We will give whoever drops by a free Yogalates lesson.
(indirect object of the verb phrase will give)
Lacey talked at length about how she had won the perogy-eating contest.
(object of the preposition about)
The problem is that my GPS is lost.
(subject complement after the linking verb is)
Call me whatever you like; you're still not borrowing my car.
(object complement referring to object me)
Al's assumption that bubble tea was carbonated turned out to be false.
(appositive, explaining noun assumption)
Other dependent clauses act as adjectives and adverbs. We can remove them and still have a complete independent clause left, with a subject and verb and any necessary complements.
That is not the case with most noun clauses. A clause acting as an indirect object or an appositive may be removable, but other types of noun clauses are too essential to the sentence to be removed. Consider these examples:
Whether you drive or fly is up to you.
I wondered if you would like to go to the barbecue.
Sandy led us to where she had last seen the canoe.
If we remove these noun clauses, what is left will not make much sense:
is up to you
I wondered
Sandy led us to
That is because, in each example, the dependent noun clause forms a key part of the independent clause: it acts as the subject, the direct object, the object of a preposition. Without those key parts, the independent clauses do not express complete thoughts.
A sentence containing a noun clause is thus the one case in which an “independent” clause may actually need a dependent clause to be complete!
Noun clauses may need to be set off by one or two commas in the following situations.
John Allen, the mayor of Riverton, is speaking tonight.
Noun clauses are nominals and can act as appositives. In that case, they may require commas if they are not essential to the meaning of the sentence:
I did not believe his original statement, that he had won the lottery, until he proved it to us.
Here, the words his original statement identify which statement is meant, so the noun clause provides information that is merely additional and not essential.
Compare this sentence to the one below:
I did not believe his statement that he had won the lottery until he proved it to us.
In this case, the noun clause is essential for identifying which statement is meant and therefore takes no commas.
Other than appositives, noun clauses do not normally require commas. However, if the clause is in an unusual position, it may require a comma:
That the work was done on time, we cannot deny.
(object of verb deny—placed first, instead of after verb)
BUT
That the work was done on time is certainly true.
(subject of verb is, in usual position—no comma)
Whatever I say, she argues with.
(object of preposition with—placed first, instead of after preposition)
BUT
Whatever I say seems to annoy her.
(subject of verb seems, in usual position—no comma)
As the above examples show, we do not normally use a comma for a noun clause acting as subject at the beginning of the sentence, because that is the usual position for a subject. However, a comma may sometimes be needed to prevent misreading:
Who the owner of this money is, is a mystery.
Whatever property Alexandra still had, had increased greatly in value.
In the above examples, we use a comma to separate the two identical verbs in order to avoid confusion.