A clause is just a notch more complicated than a phrase. Like a phrase, a clause is used as a particular part of speech or part of a sentence; however, unlike a phrase, a clause has a verb and its subject. Independent and subordinate are the two main types of clauses.

The Declaration of Independent Clauses

An independent (main) clause is a group of words that has a verb and its subject. Also, this group of words could stand alone as a sentence; that is, the words could make sense if they were by themselves. Here's an example:

This is one independent clause. It has a subject (cards) and a verb (fell), and it stands alone as a sentence. Now, look at this sentence:

This sentence has two independent clauses. The first — the index cards scattered on the floor — has a subject cards and a verb scattered; it could stand alone as a sentence. The second — Ora Lou and Gene had to pick them all up — has subjects (Ora Lou and Gene) and a verb (had); it also could stand alone as a sentence.

Now look:

The independent clause in this sentence is Ora Lou and Gene had just alphabetized the index cards. Although the rest of the sentence — when the cards fell on the floor and scattered everywhere — has a subject (cards) and verbs (fell and scattered), it can't stand alone as a complete thought; because of this, it's not an independent clause.

In a State of Dependency: Subordinate Clauses

A subordinate (dependent) clause has a verb and its subject, but it can't stand alone as a sentence. When you read the words of a subordinate clause, you can see a subject and a verb but the words don't make sense by themselves. In order for a subordinate clause to make sense, it has to be attached to another part (to some independent clause) of the sentence. A subordinate clause usually begins with a subordinating conjunction or a relative pronoun. Look at the last example in the discussion about independent clauses:

In this sentence, when the cards fell on the floor and scattered everywhere is a subordinate clause. It has a subject cards and verbs fell and scattered. But read the words alone:

when the cards fell on the floor and scattered everywhere

So, what about them? What happened next? If the terminology of clauses seems complicated, think of the relationship this way: since a subordinate clause can't stand alone, it's secondary (subordinate) to the main clause of the sentence. Or, a subordinate clause relies (is dependent) on another clause (an independent clause) that's in the same sentence.

English has three types of subordinate clauses, and each acts in a different way in a sentence.

Adjective Clauses

An adjective clause is a subordinate clause that acts as an adjective; it modifies or describes a noun or pronoun. Looked at a different way, an adjective clause answers which one? or what kind of? An adjective clause is sometimes called a relative clause because relative pronouns (who, whose, whom, which, and that) often begin adjective clauses and relate the clause to the person, place, or thing that they describe.

Whom I knew in high school is an adjective clause. It has a verb (went) and its subject (I), and it can't stand alone as a sentence — that's what makes it a subordinate clause. It's an adjective clause because it describes the noun man; in addition, it answers the question which one? about man.

Careful! Just to confuse you, sometimes an adjective clause has that deleted from it.

Noun Clauses

A noun clause is a subordinate clause that acts as a noun; it can be the subject, predicate nominative, appositive, object of a verb, or object of a preposition. A noun clause answers who? whom? or what?

What they heard at the library is a noun clause. It has a subject (they) and a verb (heard) and it can't stand alone as a sentence, so it's some type of subordinate clause. Because it's the direct object of couldn't believe (and therefore functions in the sentence as a noun), it's a noun clause.

Adverb Clauses

An adverb clause is a subordinate clause that acts as an adverb; it can modify or describe a verb, an adjective, or another adverb. Looked at in a different way, an adverb clause answers when? where? how? why? to what extent? with what goal or result? or under what condition or circumstances? An adverb clause is introduced by a subordinating conjunction, such as after, although, as (if), because, once, until, and while.

Because he was attracted to her is an adverb clause. It has a subject (he) and a verb (was attracted). It can't stand alone as a sentence, so it's some type of subordinate clause. Because it modifies the verb visited, it's an adverb clause.

Remember to use a comma after an introductory adverb clause, as in this example:

Using Clauses

By eliminating the noun or pronoun and changing the verb, you can change clauses into phrases; in the same vein, you can add a subject and verb to a phrase and create a clause. Why would you want to change clauses into phrases (or vice versa)? After you've written a paragraph, you might notice that you've used the same style in several sentences, and because of that your writing seems monotonous or “sing-songy.” Reconstructing your sentences by changing clauses and phrases might help eliminate that effect and make your paragraph livelier. Notice the difference here:

Adjective clause: The green van that is on the used car lot caught my eye.

Adjective phrase: The new green van on the used car lot caught my eye.

By the same token, you can convert a subordinate clause into an independent clause by adding a few words: