Babel Bible

22.01.22 · grammar / style

Parallel structure

draft3 tiersLean: none

Anchor (Master): academic sources

Intuition [Beginner]

Parallel structure means using the same grammatical form for items in a list, a comparison, or a paired construction. When all items match, the sentence reads smoothly. When they do not, something feels off.

In lists, every item should be the same kind of word or phrase:

  • Parallel: "She likes hiking, swimming, and biking." (all -ing words)
  • Not parallel: "She likes hiking, swimming, and to bike." (mixed -ing and to- form)

With coordinating conjunctions (and, but, or, nor), the elements on each side should match:

  • Parallel: "He works quickly and accurately." (both adverbs)
  • Not parallel: "He works quickly and with accuracy." (adverb vs. prepositional phrase)

With correlative conjunctions (either...or, neither...nor, not only...but also, both...and), the two parts should match:

  • Parallel: "She is not only a talented writer but also a skilled editor." (both noun phrases)
  • Not parallel: "She is not only a talented writer but also edits skillfully." (noun phrase vs. verb phrase)

In comparisons (using than or as), the compared elements should be grammatically parallel:

  • Parallel: "It is easier to write than to speak." (both infinitives)
  • Not parallel: "It is easier to write than speaking." (infinitive vs. gerund)

The rule is simple: match the pattern. If the first item is an -ing word, make them all -ing words. If the first item starts with "to," make them all start with "to."

Visual [Beginner]

PARALLEL LISTS:

  GOOD:  She likes hiking, swimming, and biking.
             ^^^^^^   ^^^^^^^^^     ^^^^^^
             (all gerunds / -ing forms)

  BAD:   She likes hiking, swimming, and to bike.
             ^^^^^^   ^^^^^^^^^     ^^^^^^^
             (mixed gerund + infinitive)


PARALLEL WITH COORDINATING CONJUNCTIONS:

  GOOD:  He is tall and strong.
            ^^^^     ^^^^^^^
            (both adjectives)

  BAD:   He is tall and has strength.
            ^^^^     ^^^^^^^^^^^^
            (adjective vs. verb phrase)


PARALLEL WITH CORRELATIVE CONJUNCTIONS:

  GOOD:  She either walks or bikes to work.
                ^^^^^     ^^^^^
                (both present-tense verbs)

  BAD:   She either walks or is biking to work.
                ^^^^^     ^^^^^^^^^
                (present vs. present progressive)


PARALLEL COMPARISONS:

  GOOD:  It is better to give than to receive.
                    ^^^^^^        ^^^^^^^^^^^
                    (both infinitives)

  BAD:   It is better to give than receiving.
                    ^^^^^^        ^^^^^^^^^^
                    (infinitive vs. gerund)


TEST:  Can you put each item into the sentence alone?
  "She likes [hiking]." -- works
  "She likes [swimming]." -- works
  "She likes [biking]." -- works
  All pass = parallel.

Worked example [Beginner]

1. Fix: "The new employee is reliable, creative, and works hard."

  • First two items are adjectives ("reliable," "creative"). The third is a verb phrase ("works hard").
  • Fix: "The new employee is reliable, creative, and hardworking." (all adjectives)

2. Fix: "He likes to read, writing, and to play guitar."

  • Mixed infinitives and gerund.
  • Fix: "He likes to read, to write, and to play guitar." (all infinitives)
  • Alternative fix: "He likes reading, writing, and playing guitar." (all gerunds)

3. Fix: "The course teaches students how to analyze data, present findings, and writing reports."

  • First two items are "how to + verb" phrases. The third breaks the pattern.
  • Fix: "The course teaches students how to analyze data, present findings, and write reports." (all verb base forms after "how to")

4. Fix: "She is not only an excellent teacher but also inspires her students."

  • "Not only" is followed by a noun phrase; "but also" is followed by a verb phrase.
  • Fix: "She is not only an excellent teacher but also an inspiring mentor." (both noun phrases)
  • Alternative fix: "She not only teaches excellently but also inspires her students." (both verb phrases)

5. Fix: "Running every day is healthier than to sit on the couch."

  • Gerund compared with infinitive.
  • Fix: "Running every day is healthier than sitting on the couch." (both gerunds)

Check your understanding [Beginner]

Formal definition [Intermediate+]

Parallelism (also called parallel structure or parallel construction) is the principle that coordinate, compared, or correlative elements in a sentence should have the same grammatical form. The domains where parallelism applies:

Domain Pattern Example
Lists and series A, B, and C (same category) reading, writing, and arithmetic
Compound predicates V1 and V2 (same form) She sings and dances.
Correlative conjunctions either X or Y (X, Y same form) either walk or run
Comparisons X than Y (X, Y same form) easier to read than to write
Headings and outlines consistent format throughout 1. Define, 2. Measure, 3. Analyze

Faulty parallelism occurs when items in a coordinate or comparative structure differ in grammatical category (e.g., mixing noun phrases and verb phrases, or gerunds and infinitives). The result is not necessarily ungrammatical in the strict sense, but it violates a strong stylistic convention of formal English.

The parallelism constraint operates at every level of grammatical structure:

  • Morphological: coordinate adjectives should have the same degree form (faster, more reliable, cheaper rather than faster, more reliable, and it costs less)
  • Phrasal: coordinate phrases should be of the same type (in the morning and at night rather than in the morning and nighttime)
  • Clausal: coordinate clauses should have the same structure (She said that she would come and that she would bring food)

Key concepts [Intermediate+]

  1. Parallelism and the coordinate structure constraint. In syntax, the Coordinate Structure Constraint (Ross, 1967) states that elements inside a coordinate structure cannot be extracted or moved independently. "What did she [buy __] and [sell __]?" is fine (parallel gaps), but *"What did she [buy books] and [sell __]?" is not (non-parallel extraction). This syntactic constraint reflects the deeper principle that coordination requires structural parallelism.

  2. The role of the first item as a template. In most cases of faulty parallelism, the first item in the series sets the pattern, and subsequent items break it. This makes editing straightforward: identify the form of the first item and ensure all subsequent items match. "She likes hiking (gerund), swimming (gerund), and to bike (infinitive)" -- the third item breaks the gerund pattern set by the first two.

  3. Ellipsis and parallelism. Parallelism enables elliptical coordination -- the omission of repeated material that the reader can recover from the parallel structure. "She likes hiking and [likes] swimming." The parallel structure makes the ellipsis recoverable. If the structure is not parallel, ellipsis fails: "She likes hiking and to swim" -- the reader cannot recover a single verb that governs both forms.

  4. Parallelism in rhetoric. Beyond grammar, parallelism is a powerful rhetorical device. Martin Luther King Jr.'s "I have a dream" speech uses anaphoric parallelism (repeating "I have a dream" before each clause) to build momentum. Churchill's "We shall fight on the beaches, we shall fight on the landing grounds, we shall fight in the fields" uses syntactic parallelism for rhetorical force. Grammatical parallelism and rhetorical parallelism are the same principle applied at different scales.

Linguistic theory [Master]

Coordination as a syntactic operation. In generative syntax, coordination is typically analyzed as the merging of two or more constituents of the same category under a coordination phrase (CoordP). The coordinate structure has the form [CoordP [XP and [YP]]], where XP and YP must be of the same category. This category matching requirement is the syntactic foundation of parallelism.

Chomsky (1957) noted that coordination is one of the few constructions that reveals constituent structure. "She [VP reads books] and [VP writes articles]" shows that "reads books" and "writes articles" are both VPs, because coordination requires matching categories. The ungrammaticality of *"She [VP reads books] and [NP the newspaper]" follows from the category mismatch.

The semantic basis of parallelism. Parallelism is not purely syntactic. Gazdar et al. (1985) propose that coordination requires semantic category matching rather than syntactic category matching. Under this analysis, "She is [AP fond of tea] and [NP a lover of coffee]" is acceptable because both phrases denote properties of the subject, even though they have different syntactic categories (AP vs. NP). This predicts a broader range of acceptable coordinations than a purely syntactic account.

Processing and parallelism. Psycholinguistic research shows that parallel structures are processed more efficiently than non-parallel ones. Frazier et al. (2000) found that readers expect continuation in the same syntactic category after processing the first conjunct. When the second conjunct violates this expectation (faulty parallelism), processing time increases. This supports the view that parallelism is not merely a stylistic convention but reflects a cognitive preference for structural consistency.

Cross-linguistic parallelism. The parallelism requirement is not unique to English. Coordinate structures in most languages require matching categories, though the specific constraints vary. In languages with rich case systems (German, Russian), coordinated NPs must agree in case. In languages with serial verb constructions, parallelism between verb phrases is the default. The universal tendency toward structural parallelism in coordination suggests that it reflects a fundamental property of the human language faculty.

Historical context [Master]

Parallelism has been recognized as a rhetorical and grammatical principle since antiquity. Aristotle's Rhetoric (4th century BCE) discusses parisosis (clauses of equal length) and paromoiosis (similar clause structure) as devices for creating persuasive prose. The Latin rhetoricians called parallel constructions membrum (balanced clauses) and isocolon (clauses of equal length and structure).

In English, parallelism was a central principle of classical prose style. The King James Bible (1611) is a masterclass in parallel structure: "To every thing there is a season, and a time to every purpose under the heaven: a time to be born, and a time to die; a time to plant, and a time to pluck up that which is planted." The repeated "a time to X, and a time to Y" structure creates the rhythm and memorability for which this passage is known.

The 18th-century grammarians did not explicitly formulate a "parallelism rule" as such. The principle was taught implicitly through the study of classical rhetoric and through models of good prose. The explicit treatment of parallelism as a grammatical requirement emerged in 20th-century composition pedagogy, where it became a standard topic in handbooks and textbooks.

The term "parallel structure" or "parallel construction" became standard in American English composition textbooks in the mid-20th century. Strunk and White's The Elements of Style (1959) devotes a full section to parallel construction, giving it the status of a fundamental principle: "Express coordinate ideas in similar form."

The teaching of parallelism as an error-avoidance strategy (identifying and fixing "faulty parallelism") is largely a 20th-century development, reflecting the influence of standardized testing and composition pedagogy on grammar instruction.

Bibliography [Master]

  • Aristotle. (4th c. BCE). Rhetoric.
  • Chomsky, N. (1957). Syntactic Structures. Mouton.
  • Frazier, L., Munn, A., & Clifton, C. (2000). Processing coordinate structures. Journal of Psycholinguistic Research, 29(3), 343-370.
  • Gazdar, G., Klein, E., Pullum, G.K., & Sag, I.A. (1985). Generalized Phrase Structure Grammar. Harvard University Press.
  • Huddleston, R. & Pullum, G.K. (2002). The Cambridge Grammar of the English Language. Cambridge University Press.
  • Ross, J.R. (1967). Constraints on Variables in Syntax. MIT dissertation.
  • Strunk, W. & White, E.B. (1959). The Elements of Style. Macmillan.