2.4 Parallel Structure and Faulty Comparisons

What is Parallel Structure?

Parallel structure, also known as parallelism, is a stylistic and grammatical principle that requires related ideas to be expressed in the same grammatical form. Just as parallel lines run alongside each other in perfect alignment, parallel sentence elements should align grammatically. When words, phrases, or clauses in a sentence are balanced, the writing flows smoothly and is easy to read. When parallelism is broken, the sentence sounds awkward, clunky, and structurally flawed.

The most common place you will need to enforce parallel structure is when writing items in a list or a series. If the first item in a list is an infinitive verb, all subsequent items must be infinitive verbs. If the first item is a noun, all others must be nouns.

Incorrect (Not Parallel): The company expects its employees to be punctual, working hard, and they should be professional.

Look at the items in this list: "to be punctual" (infinitive phrase), "working hard" (participle phrase), and "they should be professional" (independent clause). Because they are all formatted differently, the sentence lacks parallel structure.

Corrected (Parallel): The company expects its employees to be punctual, hardworking, and professional. (All three items are now adjectives.)

Corrected Alternate (Parallel): The company expects its employees to arrive on time, to work diligently, and to behave professionally. (All three items are now infinitive phrases.)

Parallelism with Correlative Conjunctions

Parallel structure is also strictly required when you use correlative conjunctions. These are pairs of conjunctions that work together to join sentence elements. The most common correlative conjunctions are:

• Either... or...
• Neither... nor...
• Not only... but also...
• Both... and...

The rule of parallelism states that whatever grammatical structure follows the first half of the pair must exactly match the grammatical structure that follows the second half of the pair.

Incorrect: The new software is not only fast but also it is easy to use.

In this sentence, the first half of the conjunction pair (not only) is followed by an adjective ("fast"). However, the second half (but also) is followed by an entire independent clause ("it is easy to use"). This breaks parallel structure.

Corrected: The new software is not only fast but also user-friendly.

Now, both halves of the conjunction pair are followed by adjectives, restoring perfect balance to the sentence. On the PERT Writing exam, always check the grammatical construction immediately following correlative conjunctions to ensure they match.

Faulty Comparisons

A faulty comparison (or illogical comparison) is a specific type of structural error where a writer attempts to compare two things that cannot logically be compared. This usually happens when a writer omits words in an attempt to be concise, accidentally creating a comparison between a person and a thing, or between two entirely different categories of items.

In English grammar, you must always compare apples to apples. You can compare one person's salary to another person's salary, but you cannot compare a salary to a person.

Incorrect (Faulty Comparison): The salary of a software engineer is generally higher than a high school teacher.

Read the sentence carefully. What two things are being compared? The sentence compares "the salary of a software engineer" directly to "a high school teacher" (the actual human being). It is completely illogical to compare a sum of money to a person.

Faulty comparisons are highly deceptive because our brains naturally fill in the missing information. When we read the incorrect sentence above, we understand what the writer meant to say, so the error doesn't immediately stand out. However, on a grammar test, you must focus on what is literally written on the page.

Fixing Faulty Comparisons

To correct a faulty comparison, you must add words to the sentence to ensure that the two items being compared are grammatically equivalent. There are a few standard ways to fix this error.

Method 1: Use "That Of" or "Those Of"

The most common and formal way to fix a faulty comparison is to use the pronoun phrase "that of" (for singular nouns) or "those of" (for plural nouns) to stand in for the first item being compared.

Error: The tail of a fox is bushier than a dog. (Comparing a tail to a dog.)

Correction: The tail of a fox is bushier than that of a dog. (The pronoun "that" replaces the word "tail." Now, you are correctly comparing a fox's tail to a dog's tail.)

Error: The test scores of the morning class were higher than the afternoon class. (Comparing plural scores to a singular class.)

Correction: The test scores of the morning class were higher than those of the afternoon class. (The pronoun "those" replaces the plural word "scores.")

Method 2: Use Possessive Nouns

Another effective way to fix a faulty comparison is to use an apostrophe and an "s" to make the second item possessive. This implies the missing word.

Error: My sister's car is much faster than my brother. Correction: My sister's car is much faster than my brother's.

By adding the possessive "'s," the sentence logically implies "my brother's car," making the comparison parallel and correct.