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A clause is essentially a phrase, but with both a subject and predicate (more on those in the next post). Clauses are either dependent or independent. An independent clause can exist by itself as a complete sentence (as in “I love grammar.”), while a dependent clause cannot.
Dependent or Subordinate Clauses
A dependent or subordinate clause depends on an independent clause to express its full meaning (as in “Because I love grammar.”). These clauses begin with a dependent word, like a subordinating conjunction or a relative pronoun.
Dependent clauses can function as nouns, adjectives, and adverbs:
- Noun Clause - "The boy wondered if his parents bought him what he wanted for Christmas." A noun clause can replace any noun in a sentence, functioning as a subject, object, or complement (see English Grammar: Basic Sentence Elements).
- Adjective Clause (or relative clause) - "I listened to the song that you told me about." An adjective clause describes a noun just like an adjective. Which song? The new song, the good song, the song that you told me about. Often called relative clauses, they're either restrictive or nonrestrictive (also called defining and non-defining, essential and nonessential, or integrated and supplementary):
- Restrictive Clause - "The building that they built in San Francisco sold for a lot of money." A restrictive clause begins with a relative pronoun like that or who (or sometimes which -- see Which Versus That). It specifies or restricts the noun; in this case, it specifies which building the speaker is referring to. Note: the relative pronoun is often omitted ("The building (that) they built"), leaving what is called an elliptical clause or contact clause.
- Nonrestrictive Clause - "The building, which they built in San Francisco, sold for a lot of money." A nonrestrictive clause begins with a relative pronoun like which or who. It adds extra information about an already-specific noun; in this case, there's only one building to talk about, whereas the example for the restrictive clause implies that there could be several buildings.
- Adverb Clause - "I'll do the laundry when I'm out of clothes." Like all adverbials, adverb clauses express when, where, why, and how something occurs. A dependent clause is an adverb clause if you can replace it with an adverb, as in "I'll do the laundry later."
Note: appositives can include clauses, but I’ve yet to find a source mentioning an “appositive clause.” They’re generally regarded as a type of noun phrase, even though they can be restrictive or nonrestrictive like relative clauses.