Core Philosophy: Like With Like
Parallelism requires that grammatically equivalent ideas be expressed in grammatically equivalent forms. When a sentence lists, compares, or correlates items, each item must have the same grammatical structure as the others.
The key insight is that the coordinator (and, but, or, not only...but also, both...and, either...or) signals parallelism. Everything it connects must be in the same form: all nouns, all infinitives, all gerunds, all clauses — never mixed.
Core Insight: Find the coordinator, identify what it connects, then verify all connected items share the same grammatical form.
Anatomy of Parallel Structure
Match-the-Form Strategy
Find the coordinator
And, but, or, nor, not only...but also, both...and, either...or, whether...or, as...as — these signal parallelism requirements.
Identify the anchor element
The first item in the parallel series sets the grammatical form. Every subsequent item must match it.
Check each element against the anchor
Read across the parallel items: is each one the same grammatical form (noun, verb, adjective, clause)?
Eliminate mismatched choices
Any answer choice that breaks the form of the anchor element is wrong, even if the individual phrase sounds natural.
Worked Examples
10 Parallelism Traps
1. Gerund-infinitive mismatch
Mixing "to do" and "doing" in a parallel list.
2. Noun-verb mismatch
Listing a noun alongside a verb phrase without parallel structure.
3. Clause-phrase mismatch
One item is a full clause (with a verb) while another is just a phrase.
4. Comparison parallelism failure
Comparing a noun to a clause or a person to an attribute.
5. "Not only...but also" imbalance
Each side of the correlative conjunction must be grammatically identical.
6. "Both...and" trap
Items after "both" and after "and" must be the same form.
7. Hidden parallel structure
Parallelism required between items separated by many words — easy to miss.
8. Article/preposition dropping
Dropping "the" or "a" in later items when it was present in the first.
9. Mixed active-passive
Switching from active to passive voice within a parallel series.
10. "As...as" comparison trap
Both sides of "as...as" must compare equivalent elements.
Parallel Connectors Quick Reference
| Connector | What it connects | Example |
|---|---|---|
| and, but, or, nor | Any grammatically equivalent elements | fast, cheap, and reliable |
| not only...but also | Must be same form on both sides | not only improved but also simplified |
| both...and | Same form on each side | both efficient and accurate |
| either...or / neither...nor | Same form on each side | either approve or reject |
| whether...or | Clauses or verb phrases | whether to proceed or to wait |
| as...as | Parallel elements being compared | as useful as it is elegant |
10 GMAT-Style Practice Questions
Select your answer, then reveal the step-by-step explanation. Each question reflects real GMAT difficulty and format.
The project team was responsible for designing the prototype, testing its functionality, and [to present/presenting/the presentation of/presented] the results to senior management. Which form correctly completes the parallel structure?
The new trade policy not only reduced tariffs on imported goods but also [increased/the increase of/increasing/to increase] domestic manufacturing incentives. Which is correct?
Critics argued that the documentary was poorly researched, [ideological bias/ideologically biased/biased ideologically/showing ideological bias], and missing key historical context. Which correctly maintains parallel structure?
The executive's responsibilities include managing a team of 50 analysts, overseeing quarterly budget planning, and [to ensure/ensuring/ensure/the ensuring of] compliance with regulatory standards. Which is correct?
The report found that housing costs in City X were significantly higher than [City Y / in City Y / those in City Y / what City Y's were]. Which version makes the comparison parallel and logical?
The startup's success can be attributed both to its innovative product design and [its aggressive marketing strategy / to its aggressive marketing strategy / aggressive marketing / to aggressively market]. Which is correct?
Successful negotiators are skilled at listening carefully to the other party, identifying areas of common ground, and [making/to make/they make/made] concessions strategically. Which is correct?
The audit committee concluded that the irregularities were neither accidental [nor/or/but/and] confined to a single department. Which connector is correct?
The new regulation requires manufacturers to disclose all ingredients, to provide clear usage instructions, and [to label/labeling/labels/labeled] potential allergens prominently. Which is correct?
Working from home offers employees the flexibility to set their own schedules, to avoid long commutes, and [to better balance/for balancing better/a better work-life balance/better balancing] personal and professional responsibilities. Which is correct?
Key Takeaways
And, but, not only...but also — these signal what must be parallel. Find them before anything else.
The first item sets the form. Every other item must match: all infinitives, all gerunds, all nouns.
Use "that of" or "those of" to compare equivalent nouns. Never compare a noun to a clause.
Both...and, not only...but also, either...or — each side must be grammatically identical.