Essentially, a noun clause is a phrase or part of a sentence that acts as a noun. The noun clause functions in the same way as a noun or pronoun, establishing a subject or object in the sentence. A noun is generally accepted to be a person, a place, or a thing. In a sentence, the noun serves as the primary focus.
For the most part, a noun will answer who or what about the verb, which is the sentence’s action word. Noun clauses generally are the same as nouns, except that they are made up of two or more words, and nouns are single words. For example, in the sentence "Leslie did not know that her friend could sing," the word “Leslie" is a noun, and the phrase “that she could sing” is a noun clause.
The easiest way to identify a phrase as a noun clause is to locate the verb in the sentence and then ask who or what about it. “Know” acts as the verb in the example sentence. The answer to the question "What didn’t Leslie know?" is "that her friend could sing." Thus, “that her friend could sing” is a noun clause in this sentence.
There are three main types of noun clauses. The first type of noun clause begins with a question word, such as who, what, where or when. In the sentence "It doesn’t matter where we are going for dinner," the phrase “where we are going for dinner” is a noun clause.
Other noun clauses start with either “whether” or “if,” as in the sentence "He can’t decide whether to go." “Decide” is the verb in this sentence. “Whether to go" explains what he can’t decide and is a noun clause.
The third main type of noun clause begins with “that.” The first example, “Leslie didn’t know that her friend could sing,” shows this type of noun clause. “That her friend could sing” works as an object in this sentence.
Just like nouns, noun clauses can operate in several ways within a sentence. A noun clause can take the place of the noun and work as the subject or object of a verb. In the sentence "What the team did shocked its fans," the phrase “what the team did” is the subject of the sentence and acts as a noun clause in place of a single noun.
Noun clauses also can be used as object prepositions in a sentence or as subject complements. In the sentence "The players' mistake was that they refused to play zone defense," the phrase "that they refused to play zone defense” is a subject complement. Although “the players' mistake” is actually the subject in the sentence, “that they refused to play zone defense” is a complement to that subject.
Although noun clauses can be somewhat trying to understand, they are relatively easy to identify after one understands what they are and how they work. Sometimes it takes more than one word to fully express an idea or to fully answer a question. When this happens, a noun clause is often used in place of the noun itself.