Clauses and Phrases

Complex sentences are combinations of phrases and clauses. Most writers know this, but they cannot remember how to distinguish the two. We understand — we can’t remember much of the time, either. We suggest studying clauses before examining phrases, which can be confusing.

Understanding clauses and phrases helps writers avoid errors such as dangling modifiers, fused sentences, comma splices, and fragments. It is possible to write a long sentence that is a fragment because the primary clause is lost among the clutter of words.


A clause is a part of a sentence that contains its own subject and verb but is not the complete sentence. What can be confusing is that some clauses could stand alone as sentences. When searching for clauses in sentences, look for verbs and their subjects.

Independent Clauses

An independent clauses is also known as a primary, main, and principal clause. An independent clause has a subject and verb, with the ability to stand alone as a sentence.

Charles went to dinner after he changed clothes.

Charles went to dinner.

The independent clause is a short sentence. It is the primary clause because it contains the simple subject and simple predicate of the full sentence.

Compound Sentences

A compound sentence is a sentence formed by two or more independent clauses. Use a comma to separate long independent clauses joined by and, but, or, or nor. Place the comma before the conjunction.

Wendy plans to attend college, but she needs to earn better grades.

Dependent Clauses

A dependent clause, or subordinate clause, adds information to the sentence by acting as an adjective, adverb, or noun. Frequently, a dependent clause is introduced by a subordinate conjunction. Look for either commas or conjunctions to identify dependent clauses.

Martha told us that her book is missing.

The book, which was her favorite, has a blue cover.

In the first example, “that” introduces the dependent clause. If we were to replace “that” with a period, the resulting sentences could stand alone with reduced clarity. Our second sentence features a dependent clause marked by commas. Alone, the clause poses a question. In the appositive form, it adds a description of the book to the sentence.

Adjective Clauses

An adjective clause acts as an adjective, modifying a noun or pronoun. Use an adjective clause when an adjective or two will not suffice. Often, the relative pronouns who, whose, whom, which, and that attach adjective clauses to their antecedents.

The writer who wins the award must deliver an acceptance speech.

Adverb Clauses

An adverb clause (not adverbial) acts as an adverb and indicates the time, manner, or degree of an action. Adverb clauses often begin with subordinate conjunctions.

He bought the house after he saw the roof-top greenhouse.

Noun Clauses

A noun clause is a clause acting as a noun, sometimes as the subject of a sentence. If you can replace the clause with it, you have identified a noun clause.

How he thinks is a mystery to me.

It is a mystery to me.

Essential and Nonessential Clauses

A clause can be essential or nonessential based on the writer’s intention and the construction of the sentence. As the names imply, an essential clause is needed to clarify the sentence, while a nonessential clause adds information that might not be required.

Essential Clauses

An essential clause usually follows a noun or pronoun and clarifies the noun’s identity. We use an essential clause when there might be a doubt as to who is being mentioned in a sentence.

The boy seldom speaks.

With an essential clause:

The boy who sits in the back seldom speaks.

In the example, we might not know the identity of the boy without additional information. By describing where the boy sits, it is easier to identify the particular person mentioned.

Sometimes an essential clause can be replaced with an adjective. A writer must decide which construction is most effective.

An editor who is talented respects the author’s style.


A talented editor respects the author’s style.

Nonessential Clauses

A nonessential clause interrupts the flow of a sentence with additional information that is not essential for clarity. Because a reader or speaker pauses at the information, a nonessential clause is set off with commas, like an appositive.

Sometimes it is best to pull a nonessential clause from a sentence and make it a short sentence that follows the original. If a nonessential clause describes an important detail, consider rewriting the sentence.

The boy, who sits in the back, is the only male student.

The boy is the only male student. He sits in the back.

The pair of shorter sentences might be more effective than a long sentence. The status of the boy is stated, then how he seems to relate is described. This pattern is more effective than using a nonessential clause in some situations.

Elliptical Clauses

An elliptical clause is a clause in which certain words are understood without being said or written. As in most languages, English allows for the omission of words when they are obvious by nature of context or grammar.

What will happen if I miss the deadline?


What if I miss the deadline?

She enjoys history more than she enjoys math.


She enjoys history more than math.


A phrase is a group of words that cannot function as a sentence. A phrase acts together, as if the words of the phrase are a single word. Phrases act as nouns, adjectives, and adverbs. There are five basic types of phrases:

  • Prepositional
  • Verb
  • Infinitive
  • Gerund
  • Participial

Prepositional Phrases

A prepositional phrase begins with a preposition and ends with nouns or pronouns. The noun or pronoun is the object of the preposition. Most prepositional phrases act as adjectives or adverbs.


The student with the best grades is also a great athlete.


We attended a concert at the park.

Read the section on prepositions for more information.

Verb Phrases

Verb phrases include a primary verb and any auxiliaries accompanying the verb. A common error is splitting a verb phrase with an adverb. You should place adverbs before or after the verb phrase.

Infinitive Phrases

Infinitive phrases are verbal phrases that begin with an infinitive. Grammarians include any final adverb as part of the phrase.

He wanted to write.

She expects to be published soon.

Gerund Phrases

A gerund phrase is a group of words containing a gerund, but not acting as the verb phrase within a sentence. In fact, the gerund acts as a noun, possessed by another noun or pronoun.

Your nagging him isn’t making the publisher happy.

In the example, nagging him is a gerund phrase, owned by the person being addressed as you in the dialogue. The entire phrase can be replaced with the pronoun it to test whether or not the word group is actually a gerund phrase.

It isn’t making the publisher happy.

Participial Phrases

Participial phrases are groups of words beginning with participles. Participial phrases tend to act like adjectives or adverbs, though they can replace nouns. We have read claims that participial phrases only act as adjectives.


An appositive explains or describes the noun or pronoun it follows. Appositives are set apart by commas. Predicate nouns and appositives are similar when reflecting the meaning of the subject in a sentence. Use appositives for concise writing, eliminating predicate noun sentences.

The boysenberry, a blackberry and raspberry hybrid, originated at Knott’s Farms in California.

The boysenberry is a hybrid of the blackberry and raspberry. Boysenberries originated at Knott’s Farm in California.

In the example, hybrid is a noun describing the boysenberry plant. This relationship is clear in the predicate noun form. Using the appositive, we eliminated the need for boysenberries.

A simple test for appositives is to replace the first comma with is and the second with a period. If the result is a predicate noun or predicate adjective, you have identified an appositive.

The student like Mr. Wallace, the new teacher.

Mr. Wallace is the new teacher.

Some grammarians insist appositives are phrases, not clauses, while others define appositives as all phrases and clauses set off with commas.


A parenthetical comment is an appositive stating the opinion of a speaker, narrator, or author. As the name implies, a parenthetical is sometimes punctuated with parentheses instead of commas.

Jason, liar that he is, never told her he had found the book.

Jason (a liar) never told her he had found the book.


A contrasting expression is an appositive beginning with a negative conjunction, such as but, however, not, or though. The contrast modifies a noun or pronoun.

The bee, though not aerodynamic, flies well.

Coins, however shiny, are merely money.

Appositive Adjectives

Using appositive adjectives emphasizes the description of a noun or pronoun. Appositive adjectives are placed after the noun or pronoun and set off with commas.

Her hair, long and golden, reflected the sunlight.

Use appositive adjectives sparingly, because they intentionally slow a reader.


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Writer: C. S. Wyatt
Updated: 30-Nov-2013
Editor: S. D. Schnelbach