GMAT Sentence Correction Preparation: Comparison and Parallelism

GMAT Sentence Correction is a toughie. During GMAT preparation, you think you’ve nailed the verbal fundamentals, you get down to tackling the tough SC questions and realize you aren’t there yet.  The GoGMAT tutors are back on MBA Crystal Ball to share GMAT verbal tips and sample questions to explain two key concepts within Sentence Correction questions.

GMAT Sentence Correction: Comparison and Parallelism

Flaws in parallel structure are one of the most frequently tested error types in GMAT Sentence Correction problems. To spot such mistakes, you should remember that items in a list, parts of a comparison, and elements of correlative expressions must have identical grammatical form and be logically similar to each other. In this article, you will review the most important rules of parallelism and, using a real GMAT question as an example, see how those rules might be tested in SC problems.

Items on a list

Any sentence that lists several things must do it in a parallel manner. Consider the following sentence correction example:

The manager was not satisfied with the report because it was biased, superficial, and the writing was poor.

This sentence lists three criticisms of a report. The last item on the list stands out because, unlike the first two, it is not expressed with an adjective. To make this list parallel, you must consistently use a single grammatical form. In this case, the simplest form is the adjective:

The manager was not satisfied with report because it was biased, superficial, and poorly written.

Whenever you encounter a sentence that lists several items, pay particular attention to articles and prepositions: GMAT is keen on violating parallelism by omitting these parts of speech or introducing them where they are not needed. Remember that an article or a preposition that applies to all items on the list must either be used only before the first item or be repeated consistently before each.

Correlative expressions

Elements of such phrases as both X and Y, not only X but also Y, either X or Y, and neither X nor Y should have the same grammatical form. Violations of this rule are usually corrected by rearranging the sentence. Look at the following sample sentence correction question:

Either you are required to submit the paper on time or ask your professor for an extension.

By using the correlative expression either…or…, this sentence intends to list two options available to someone writing a paper. However, it fails to do so in a parallel manner because either is followed by the pronoun you, whereas or is followed by the verb ask. Since the two parts of this expression must have the same form, a correct version of the sentence might read:

You are required either to submit the paper on time or to ask your professor for an extension.


Comparison is another type of structure whose elements must be parallel. Whenever you see clue words such as like, unlike, more/less than, as many/much as, in contrast with, or in comparison to, you must check whether the comparison is expressed in parallel terms with regard to both grammar and meaning. To be grammatically and logically parallel, comparisons must be complete and unambiguous. Look at the following example:

Attending a private college is significantly more expensive than a state school.

This sentence is both grammatically and logically incorrect because it attempts to compare attending, a gerund, with school, a noun. To maintain parallelism, you can compare either a private college with a state school or attending the one with attending the other. The correct sentence might thus read:

Attending a private college is significantly more expensive than going to a state school.

Keeping in mind the above information, try to answer the following sentence correction question.

Like humans, who can recognize another’s knowledge and beliefsan ability that may not be unique to mankind—reading others’ intentions and displaying awareness of what others see seem within the capabilities of some some non-human primates.

A. reading others’ intentions and displaying awareness of what others see seem within the capabilities of some some non-human primates.

B. the capabilities of some non-human primates include reading others’ intentions and displaying awareness of what others see.

C. some non-human primates seem capable of reading others’ intentions and displaying awareness of what others see.

D. some non-human primates‘ ability to read others’ intentions and displaying awareness of what others see.

E. non-human primates, reading others’ intentions, seem to have some abilities of displaying awareness of what others see.

The sentence begins with like, which should immediately prompt you to determine what is being compared and see whether the parts of the comparison are expressed in parallel terms. If you ignore the two modifiers that stand between the compared objects here, you will see that the sentence attempts to point out a similarity between humans and the abilities of primates (reading… and displaying…) However, we can only logically compare humans and primates or the abilities of humans with those of primates. Since the beginning of the sentence cannot be changed, its underlined part should begin with some non-human primates.

A. Illogically and ungrammatically compares humans with reading and displaying.

B. Humans cannot be compared with the capabilities of some non-human primates.

C. Correct.

D. Although the underlined portion of the sentence begins with some non-human primates, its subject is ability, and it is ability that is compared with humans, so the comparison remains illogical. Moreover, the underlined part is missing a main verb, thus making the whole sentence incomplete.

E. Distorts the original meaning by misplacing some, which now refers to abilities instead of non-human primates. Moreover, the original sentence lists reading others’ intentions and displaying awareness of what others see as two things that some non-human primates are capable of. In Choice D, these two are no longer listed in a parallel manner.

Continue learning on our GMAT prep discussion forum. If you have any GMAT related questions about this post or any other GMAT topic, head over to the GMAT preparation helpdesk and shoot your queries.

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// Sameer Kamat
Sameer Kamat
Founder of MBA Crystal Ball. Author of Beyond The MBA Hype & Business Doctors. Here's more about me. Connect with me: Linkedin | Facebook | Twitter | Youtube

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