4.1 Parallel Structure & Correlative Conjunctions

Parallel Structure & Correlative Conjunctions

Core Principle: Parallel structure (also called parallelism) requires that two or more phrases or clauses in a sentence sharing the same grammatical function also share the same grammatical form. On the HiSET Language Arts – Writing test, faulty parallelism is one of the most frequently tested sentence structure errors, appearing in lists, correlative conjunction pairs, and comparative constructions.

When a sentence links multiple ideas using coordinating conjunctions (and, but, or), correlative conjunction pairs (either...or, not only...but also), or comparative markers (than, as...as), the human brain expects those ideas to follow a predictable, matching grammatical pattern. When the pattern breaks—for instance, pairing an infinitive with a gerund or a noun phrase with a dependent clause—the sentence becomes unbalanced, clumsy, and difficult to process. In standardized editing passages, recognizing parallel structure is essential for restoring rhetorical balance and syntactic precision.

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The Foundational Rule of Parallelism

The fundamental rule of parallelism states: Grammatically equivalent ideas must be stated in grammatically equivalent forms.

If the first item in a series is a gerund phrase (a verb ending in -ing acting as a noun), every subsequent item in that series must also be a gerund phrase. If the first branch of a correlative conjunction contains a prepositional phrase, the second branch must contain an identical prepositional phrase structure.

[Non-Parallel]: The supervisor praised the team for working efficiently, their innovative thinking, and to meet tight deadlines.
[Parallel]:     The supervisor praised the team for working efficiently, thinking innovatively, and meeting tight deadlines.

In the non-parallel example above, the list consists of a gerund phrase (working efficiently), a noun phrase (their innovative thinking), and an infinitive phrase (to meet tight deadlines). The parallel revision aligns all three items into uniform gerund phrases (working..., thinking..., meeting...), creating immediate rhythm and grammatical harmony.

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Parallelism in Lists and Series

On the HiSET exam, lists and series of three or more items appear frequently in workplace memoranda, policy proposals, and academic summaries. Items in a series can take several grammatical forms, but whichever form is established by the initial item must govern all remaining items.

1. Gerund Phrases vs. Infinitive Phrases

• Faulty: The director’s responsibilities include coordinating departmental budgets, to supervise senior staff, and evaluation of quarterly performance metrics.
• Parallel (All Gerunds): The director’s responsibilities include coordinating departmental budgets, supervising senior staff, and evaluating quarterly performance metrics.
• Parallel (All Infinitives): The director’s responsibilities include to coordinate departmental budgets, supervise senior staff, and evaluate quarterly performance metrics.

Note on Infinitives: In a series of infinitives, the particle to may either be repeated before every verb (to coordinate, to supervise, and to evaluate) or used only once before the first verb to govern the entire series (to coordinate, supervise, and evaluate). However, switching unpredictably between including and omitting to within the same series violates parallelism.

2. Prepositional Phrases

• Faulty: The field researchers collected soil samples in the river valley, across the arid plateau, and where the forest was dense.
• Parallel: The field researchers collected soil samples in the river valley, across the arid plateau, and through the dense forest.

3. Noun Phrases and Modifiers

• Faulty: The job applicant impressed the hiring committee with her technical expertise, interpersonal poise, and because she was dedicated.
• Parallel: The job applicant impressed the hiring committee with her technical expertise, interpersonal poise, and professional dedication.

4. Independent Clauses

• Faulty: The technician diagnosed the electrical fault, replacement parts were ordered by the manager, and the system was restarted by the engineer.
• Parallel (All Active Voice Clauses): The technician diagnosed the electrical fault, the manager ordered replacement parts, and the engineer restarted the system.

Series Parallelism Diagnostic Matrix

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Correlative Conjunction Symmetrical Placement

Correlative conjunctions are paired grammatical connectors that link equal sentence elements. The five essential correlative conjunction pairs tested on the HiSET exam are:

1. Either ... or
2. Neither ... nor
3. Not only ... but also
4. Both ... and
5. Whether ... or

The Law of Correlative Symmetry

The fundamental rule governing correlative conjunctions is strict positional symmetry: The grammatical structure that immediately follows the first conjunction marker must mirror the grammatical structure that immediately follows the second conjunction marker.

[Faulty Structure]:  Subject + Verb + [NOT ONLY + Verb + Noun] + [BUT ALSO + Noun]
[Correct Symmetry]: Subject + [NOT ONLY + Verb + Noun] + [BUT ALSO + Verb + Noun]
[Correct Symmetry]: Subject + Verb + [NOT ONLY + Noun] + [BUT ALSO + Noun]

Detailed Analysis of Correlative Pair Placement

Error Pattern 1: Splitting the Verb and Object Mismatch (Not only... but also)

• Faulty: The new hospital wing not only will improve emergency triage times, but also pediatric care.
  • Analysis: "Not only" precedes a modal auxiliary and verb phrase (will improve emergency triage times), but "but also" precedes only a noun phrase (pediatric care). The elements following the markers are grammatically unequal.
• Revision A (Parallel Noun Phrases): The new hospital wing will improve not only emergency triage times, but also pediatric care.
  • Analysis: "Not only" precedes the direct object emergency triage times; "but also" precedes the direct object pediatric care.
• Revision B (Parallel Verb Phrases): The new hospital wing will not only improve emergency triage times, but also expand pediatric care.
  • Analysis: "Not only" precedes improve...; "but also" precedes expand....

Error Pattern 2: Misplaced Subject Anchors (Either... or)

• Faulty: You must either submit your application by Friday, or you must request an official extension.
  • Analysis: "Either" is placed after the modal auxiliary must, but "or" is followed by an entire independent clause (you must request...).
• Revision: Either you must submit your application by Friday, or you must request an official extension. (Links two independent clauses)
• Alternative Revision: You must either submit your application by Friday or request an official extension. (Links two verb phrases)

Error Pattern 3: Unbalanced Prepositional Distribution (Both... and)

• Faulty: The economic sanctions affected trade both in agricultural commodities and manufacturing products.
  • Analysis: "Both" is followed by the prepositional phrase in agricultural commodities, whereas "and" is followed only by the noun phrase manufacturing products (omitting the preposition in or misplaced relative to in).
• Revision A: The economic sanctions affected trade in both agricultural commodities and manufacturing products. ("Both" precedes adjective + noun; "and" precedes adjective + noun).
• Revision B: The economic sanctions affected trade both in agricultural commodities and in manufacturing products. ("Both" precedes prepositional phrase; "and" precedes prepositional phrase).

Correlative Conjunction Alignment Chart

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Parallelism in Comparisons: Avoiding Faulty Comparisons

Comparisons using words such as than, as...as, more than, less than, and compared to must link elements that are logically and grammatically comparable. A widespread error on the HiSET exam is the faulty comparison (also known as an illogical comparison), which occurs when a writer mistakenly compares an attribute or part of an entity directly to another complete entity.

The "That of" and "Those of" Rule

When comparing characteristics, metrics, qualities, or components of two nouns, you cannot compare the quality of Noun A directly to Noun B. You must compare the quality of Noun A to the quality of Noun B.

[Illogical]: The wingspan of the Andean condor is significantly wider than an American bald eagle.
(This compares a measurement—wingspan—to a whole physical bird).

[Logical]:  The wingspan of the Andean condor is significantly wider than that of an American bald eagle.
(The singular pronoun "that of" stands in for "the wingspan of").

[Illogical]: The annual maintenance costs of electric vehicles are lower than gasoline-powered vehicles.
(This compares financial costs to physical vehicles).

[Logical]:  The annual maintenance costs of electric vehicles are lower than those of gasoline-powered vehicles.
(The plural pronoun "those of" stands in for "the maintenance costs of").

Faulty Comparison Analysis Table

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HiSET Step-by-Step Parallelism Editing Protocol

When encountering a sentence with coordinating conjunctions, lists, correlative pairs, or comparative markers on the HiSET exam, execute this 3-step diagnostic routine:

[Step 1: Locate the Anchor]
Identify the coordinating conjunction (and, but, or), correlative pair (not only...but also, either...or), or comparison word (than, as...as).

[Step 2: Isolate Element A]
Bracket the grammatical unit immediately preceding or following the first marker. Determine its exact structural part of speech (gerund phrase, infinitive, independent clause, prepositional phrase, noun phrase).

[Step 3: Audit Element B (and C)]
Inspect the unit following the second marker. Does it mirror Element A's exact grammatical architecture? If not, select the revision that restores identical syntax without introducing new errors.

Passage-Level Walkthrough

Original Unedited Draft (Civic Infrastructure Report)

"To address deteriorating roadways, the municipal public works commission proposed a comprehensive repair plan yesterday. The director emphasized that the department must focus on [1] resurfacing major arterial roads, to modernize traffic signal systems, and the replacement of crumbling bridges. The commission determined that the project would [2] not only require substantial state grant funding, but also local taxpayer approval would be needed. Furthermore, analysts noted that the durability of modern asphalt mixtures is far superior to [3] traditional gravel composites."

Diagnostic Breakdown & Revision

1. Segment [1] (List Parallelism): The series begins with a gerund phrase (resurfacing major arterial roads), shifts to an infinitive (to modernize...), and ends with a noun phrase (the replacement of...).
   • Revision: Align all items as gerunds: resurfacing major arterial roads, modernizing traffic signal systems, and replacing crumbling bridges.
2. Segment [2] (Correlative Symmetry): "Not only" is followed by a verb phrase (require substantial state grant funding), whereas "but also" introduces a full passive independent clause (local taxpayer approval would be needed).
   • Revision: Align both branches to share the modal would and transitive verbs: would not only require substantial state grant funding, but also necessitate local taxpayer approval.
3. Segment [3] (Comparative Parallelism): The sentence compares the durability (a property) of modern asphalt mixtures directly to traditional gravel composites (the physical material).
   • Revision: Use the singular demonstrative pronoun that of: superior to that of traditional gravel composites.