GMAT Verbal: Parallelism and Comparison in Sentence Correction

Mastering the rules of parallelism and comparison is non-negotiable for a high GMAT Verbal score. These concepts are tested with such frequency that missteps here can directly undermine your performance. Transforming these common pitfalls into a source of confidence requires the systematic approach needed to identify and correct errors with speed and precision.

The Foundation of Parallel Structure

Parallelism is the grammatical principle that items in a list or series must share the same structural form. This creates balance, clarity, and rhythm in a sentence. On the GMAT, parallelism errors are rarely subtle; the test presents structurally mismatched items and dares you to spot the break in pattern.

The most straightforward application is in a simple list: "The manager was responsible for training new staff, developing schedules, and the analysis of reports." The error is clear: two gerunds ("training," "developing") are followed by a noun phrase ("the analysis"). The parallel correction is either all gerunds (training, developing, and analyzing) or all noun phrases (the training, the development, and the analysis). Your job is to identify the list—often signaled by commas or "and"/"or"—and ensure every element matches grammatically.

This rule extends powerfully to correlative conjunctions, paired words that link equivalent elements. Common pairs include "not only... but also," "either... or," "both... and," and "neither... nor." The grammatical structure following the second half of the pair must mirror the structure following the first. Consider this error: "The policy was praised not only for its efficiency but also because it was fair." The structures "for + noun" and "because + clause" are not parallel. A correct version would be "not only for its efficiency but also for its fairness" (both prepositional phrases) or "not only because it was efficient but also because it was fair" (both clauses).

Navigating Comparison Markers: "Like" vs. "As" and Beyond

Comparisons demand strict logical and grammatical parallelism. The markers "like," "unlike," "as," and "than" are major flashpoints. The fundamental rule is that you can only compare similar things: nouns to nouns, clauses to clauses, actions to actions.

The like versus as distinction follows this rule cleanly. Use "like" to compare nouns or pronouns. Use "as" to compare clauses (which contain a verb). For example: "Like her predecessor, the CEO emphasized innovation." (Comparing "CEO" to "predecessor," both nouns). Contrast with: "The merger proceeded as we had anticipated." (Comparing the clause "The merger proceeded" to "we had anticipated").

The word "than" introduces comparative adjectives (e.g., greater than, more than, less than) and sets up a comparison. The error often lies in an illogical comparison. The sentence "The revenue of Company A is greater than Company B" is illogical. It compares "revenue" to "Company B." It must be corrected to "The revenue of Company A is greater than that of Company B" or "Company A's revenue is greater than Company B's." Always ask: "What two things are being compared?" They must be logically equivalent entities.

Advanced Parallelism and Comparison Scope

The GMAT complicates these concepts by embedding them in complex sentences. Parallel construction must be maintained across longer phrases or clauses. For example: "To invest wisely, to diversify assets, and maintaining liquidity are key financial principles." The infinitive phrases ("To invest... to diversify") are broken by the gerund "maintaining." Correcting to "Investing wisely, diversifying assets, and maintaining liquidity..." creates a parallel series of gerunds.

A more insidious error is the comparison scope error, where the comparison is logically ambiguous or overly broad. For instance: "I admire Eleanor Roosevelt more than Hillary Clinton." This is ambiguous: Do I admire Roosevelt more than I admire Clinton, or do I admire Roosevelt more than Clinton admires Roosevelt? The correct answer on the GMAT will resolve this ambiguity, typically by using a parallel clause: "...more than I admire Hillary Clinton" or "...more than Hillary Clinton does."

Another scope error involves false agency: "Compared with last year, this quarter's profits are higher." This illogically implies "this quarter's profits" are being compared to "last year." A clearer, more logical construction is "Compared with last year's profits, this quarter's profits are higher," forcing the compared nouns into parallel.

Common Pitfalls and GMAT Test Strategy

The GMAT doesn't just test your knowledge of rules; it tests your ability to apply them under pressure while avoiding attractive wrong answers.

1. The "Sounds Right" Trap: Many incorrect choices contain comparisons that are colloquially common but grammatically flawed (e.g., "different than" is often incorrect; "different from" is preferred in formal writing). Rely on the rule, not your ear. When you see a comparison marker, immediately deconstruct what two entities are being compared.
2. The Ellipsis Error: The test often omits repeated words for brevity, which is grammatically acceptable only if the omitted words are exactly the same in both parts of the parallel structure. In "She respects her colleagues more than her manager," the ambiguity is intentional. The correct parallel answer will clarify by including the necessary verb ("...than she respects her manager").
3. Misdirection with Correlatives: A favorite trick is to place a long, complex phrase after the first correlative conjunction, making it easy to forget what structure needs to be mirrored after the second. Isolate the core words immediately following "not only" and check that the words following "but also" match. Ignore the intervening descriptive fluff.
4. Overlooking the List: Sometimes the list items are separated by many words. Train yourself to spot the "and" or the serial comma and trace backward to find all items in the series. Ensure every item from the first to the last serves the same grammatical function in the sentence.

Your primary strategy for these questions is a simple, three-step process: First, scan the underlined portion and the non-underlined lead-in for comparison markers (like, as, than, unlike) or signals of a list/series. Second, immediately identify the two things being compared or all items in the list. Third, evaluate the answers based solely on which one creates a logical, grammatically parallel structure. Eliminate choices that break the pattern.

Summary

• Parallelism is structural identity: Items in a list or linked by correlative conjunctions ("not only...but also") must be in the same grammatical form (all nouns, all gerunds, all clauses, etc.).
• Compare apples to apples: Comparison markers (like, as, than) must link logically comparable entities (noun to noun, clause to clause). "Like" compares nouns; "as" compares clauses.
• Eliminate illogical comparisons: A sentence like "Her salary is higher than her boss" is illogical; it must compare "salary" to "salary" (e.g., "than her boss's").
• Resolve ambiguity: Comparisons must be clear in meaning. Ambiguous sentences like "I admire her more than my sister" are incorrect on the GMAT; the correct answer will specify "...than I admire my sister" or "...than my sister does."
• Master complex structures: Apply parallel rules consistently, even in long sentences. Watch for scope errors where the compared item is misplaced or too broad.
• Prioritize logic over sound: Use the definitive rules, not your ear, to evaluate comparisons and parallelism, as the test frequently uses colloquial but incorrect constructions as trap answers.