Writing mistakes make a negative impression on a reader (and on a grade).  Three common sentence errors are subjects and verbs that don’t agree, modifier problems, and lack of parallel structure.  By understanding parts of speech and sentence structure, these three errors can be avoided.

Subject-Verb Agreement

“Subject-verb agreement” means the subject of a sentence and the verb of a sentence must agree with each other in number.  A singular subject belongs with a singular verb, and a plural subject belongs with a plural verb.  For example:

Singular: The cat jumps over the fence.
Plural: The cats jump over the fence.

Errors in subject-verb agreement are common, especially when the subject of the sentence is separated from the verb by other words.  One way to avoid that problem is to cross out prepositional phrases and dependent clauses.  Why?  So it is easier to see the subjects and verbs.  Subjects and verbs never appear in a prepositional phrase or a dependent clause.

For example, the prepositional phrases have been crossed out here:

The students with the best grades win the academic awards.
The puppy under the table is my favorite.

That makes it easy to identify the subjects (“students,” “puppy”) and the verbs (“win,” “is”).

Dependent clauses that separate the subject and verb have been crossed out here:

The car that I bought has power steering and a sunroof.
The representatives who are courteous sell the most tickets.

That makes it easier to see the subjects (“car,” “representatives”) and the verbs (“has,” “sell”).  And it makes it very easy to see that the subjects and verbs agree in number.

Modifiers

A modifier is a word, phrase, or clause that clarifies or describes another word, phrase, or clause.  Adjectives and adverbs are modifiers.  Phrases and clauses can also work as modifiers.  Modifiers make writing more interesting, but also more prone to errors.

Two common modifier errors are misplaced modifiers and dangling modifiers.  When these errors occur, readers become confused trying to figure out what the writer meant.

A misplaced modifier is too far from the word or words it modifies.  Misplaced modifiers make a sentence awkward and sometimes unintentionally funny.  For example:

She wore a bicycle helmet on her head that was too large.

This seems to say her head was too large.  The modifying phrase “that was too large” should be closer to the word “helmet.”  The modifier is misplaced.

Corrected:  She wore a bicycle helmet that was too large on her head.

Here is another example:

The patient was referred to a physician with stomach pains.

Does the doctor have stomach pains?  The modifier “with stomach pains” is too far from the word “patient.”

Corrected:  The patient with stomach pains was referred to a physician.

A dangling modifier is a word, phrase, or clause that describes something that isn’t in the sentence.  When there is nothing to modify, the modifier is said to “dangle.”  For example:

Riding in the sports car, the world seemed to whiz by rapidly.

Who is riding in the sports car?  The modifier “riding in the sports car” is dangling.

Corrected:  When Farzad was riding in the sports car, the world seemed to whiz by rapidly.

Here is another example:

Walking home at night, the trees looked like spooky aliens.

Who is walking?  The modifier “walking home at night” is dangling.

Corrected:  As Sarah was walking home at night, the trees looked like spooky aliens.

Parallel Structure

When something is parallel to something else, they are similar in form.  For example, two parallel lines look like this:

Parallelism in writing is the use of a similar structure in related words, clauses, or phrases.  For example, these three phrases have parallel structure:

in the pool, in the forest, in the book

They feel balanced.  Also, they are easy to read and remember.

Now look at these word groups:

in the pool, forests are green, book shelf

They are different in structure.  Notice how jagged it feels to read them, and they are more difficult to remember.

Parallel structure creates rhythm and balance in a sentence.  An unbalanced sentence sounds awkward.  Read the following sentences aloud:

Kelly had to iron, do the washing, and shopping before her parents arrived.

Driving a car requires coordination, patience, and to have good eyesight.

Swimming in the ocean is much tougher than a pool.

All of these sentences contain faulty parallelism.  The construction is clunky and confusing.  In the first example, three different verb forms are used (“had to,” “do,” “shopping”). In the second example, the writer begins with nouns (“coordination,” “patience”), but ends with a phrase (“to have good eyesight”).  In the third sentence, the writer is comparing an action (“swimming”) with a thing (“a pool”).

Here are the same sentences with correct parallel structure:

Kelly had to do the ironing, washing, and shopping before her parents arrived.  (The verbs have the same structure.)

Driving a car requires coordination, patience, and good eyesight.  (The three qualities are all written as nouns.)

Swimming in the ocean is much tougher than swimming in a pool.  (One action is being compared with another action.)

When sentences use parallel structure, they sound more pleasing.  Repetition of the pattern also minimizes the work a reader has to do to understand the sentence.

An Example of Parallel Structure

Some of the most beautiful pieces of writing and many great historical speeches use parallel structure to emphasize important points and create a smooth, easily understandable idea.

For example, here is a paragraph from Martin Luther King, Jr.’s “I Have a Dream” speech:

But one hundred years later, the Negro still is not free.  One hundred years later, the life of the Negro is still sadly crippled by the manacles of segregation and the chains of discrimination.  One hundred years later, the Negro lives on a lonely island of poverty in the midst of a vast ocean of material prosperity.  One hundred years later, the Negro is still languished in the corners of American society and finds himself an exile in his own land.  And so we’ve come here today to dramatize a shameful condition.

Not only does King repeat the phrase “One hundred years later” to drill that fact into the listener’s memories, but he also uses more subtle parallel structure in “the manacles of segregation and the chains of discrimination.”  These phrases are similar in structure (article + plural noun + preposition + noun), and the words within each part are similar in form (“manacles” and “chains,” “segregation” and “discrimination”).

Great writers and speakers are aware of the power of parallel structure.