Coordination is a useful way of connecting ideas that are roughly equal in importance. But often we need to show that one idea in a sentence is more important than another. On these occasions we use subordination to indicate that one part of a sentence is secondary (or subordinate) to another part. One common form of subordination is the adjective clause--a word group that modifies a noun.
Consider how the following sentences might be combined:
My father is a superstitious man.One option is to coordinate the two sentences:
He always sets his unicorn traps at night.
My father is a superstitious man, and he always sets his unicorn traps at night.When sentences are coordinated in this way, each main clause is given equal emphasis.
What if we want to place greater emphasis on one statement than on another? We then have the option of reducing the less important statement to an adjective clause. For example, to emphasize that father sets his unicorn traps at night, we can turn the first main clause into an adjective clause:
My father, who is a superstitious man, always sets his unicorn traps at night.As shown here, the adjective clause does the job of an adjective and follows the noun that it modifies--father. Like a main clause, an adjective clause contains a subject (in this case, who) and a verb (is). But unlike a main clause an adjective clause can't stand alone: it has to follow a noun in a main clause. For this reason, an adjective clause is considered to be subordinate to the main clause.
Identifying Adjective Clauses
The most common adjective clauses begin with one of these relative pronouns: who, which, and that. All three pronouns refer to a noun, but who refers only to people and which refers only to things. That may refer to either people or things.
The following sentences show how these pronouns are used to begin adjective clauses:
Mr. Clean, who hates rock music, smashed my electric guitar.In the first sentence, the relative pronoun who refers to Mr. Clean, the subject of the main clause. In the second and third sentences, the relative pronouns which and that refer to guitar, the object of the main clause.
Mr. Clean smashed my electric guitar, which had been a gift from Vera.
Mr. Clean smashed the electric guitar that Vera had given me.
Punctuating Adjective Clauses
These three guidelines will help you decide when to set off an adjective clause with commas:
- Adjective clauses beginning with that are never set off from the main clause with commas.
Food that has turned green in the refrigerator should be thrown away.
- Adjective clauses beginning with who or which should not be set off with commas if omitting the clause would change the basic meaning of the sentence.
Students who turn green should be sent to the infirmary.Because we don't mean that all students should be sent to the infirmary, the adjective clause is essential to the meaning of the sentence. For this reason, we don't set off the adjective clause with commas.
- Adjective clauses beginning with who or which should be set off with commas if omitting the clause would not change the basic meaning of the sentence.
Last week's pudding, which has turned green in the refrigerator, should be thrown away.Here the which clause provides added, but not essential, information, and so we set it off from the rest of the sentence with commas.