Parallelism

To get across ideas of equal value or to create snazzy sentences, use parallel sentence structure. Good sentences attempt to form parallel patterns. Without this parallel structure, they can sound stilted and awkward. For instance, which sentence sounds better below?

 

(1) King Alfred tried to make the law clear, precise, and equitable.

(2) King Alfred tried to make clear laws that had precision and were equitable.

Most people would argue that the first sentence somehow "sounds better" than the second. The first sentence uses parallel structure in its adjectives. The second doesn't. If we label the parts of speech, the first sentence has this grammatical structure after the word law: [Adjective--Adjective--Adjective]. The second sentence has this grammatical structure after the word laws: [Relative Pronoun--Verb-- Direct Object--Conjunction--Verb--Adjective]. The first sentence has a clear pattern of adjective, adjective, adjective. The second sentence has no pattern at all!
To hear the difference between a parallel and non-parallel sentence, read aloud the sentences below. The red sentences are examples of "bad" or faulty parallelism. The blue sentences use parallel structure.
faulty parallelism: She revels in chocolate, walking under the moonlight, and songs from the 1930s jazz period.
good parallelism: She revels in sweet chocolate eclairs, long moonlit walks, and classic jazz music.
more good parallelism: She loves eating chocolate eclairs, taking moonlit walks, and singing classic jazz.
Do you hear the difference? What causes that distinction between "good" and "bad" sentences? Again, the difference appears in the pattern of grammar. If we dissect the sentence, the faulty sentence on top has a grammatical pattern that looks like this:

"She revels in . . . "

"chocolate," [Object of Preposition,]
"walking under the moonlight," [Gerund--Preposition--Definite Article--Object of Preposition]
"and songs from the 1930s jazz period." [Conjunction--Direct Object--Preposition--Definite Article--Adjective --Adjective--Object of Preposition]

It's all a jumbled mess of different parts of speech being used in different ways. On the other hand, the second sentence has a clear parallel pattern:

"She revels in"

"sweet chocolate eclairs," [Adjective--Adjective--Object]
"long moonlit walks," [Adjective--Adjective--Object]
"and classic jazz music." [Adjective--Adjective--Object]

The same pattern (adjective, adjective object) reoccurs in the same way. It is parallel in its structure, and thus musical and rhythmical to read and to hear spoken aloud. The second example is also parallel, just in a different pattern.

"She revels in"

"eating chocolate eclairs" [Gerund--Adjective--Object of Gerund]
"taking moonlit walks" [Gerund--Adjective--Object of Gerund]
"and singing classic jazz." [Gerund--Adjective--Object of Gerund]

Good writers attempt to form these good sentences. Here are some more examples culled from Karen Gordon's The Transitive Vampire:

• faulty parallelism: I like to eat rich deserts, playing fast card-games, and riddles.
• good parallelism: I like eating rich deserts, playing fast card-games, and solving difficult riddles.
• more good parallelism: I like to eat rich desserts, to play fast card-games, and to solve difficult riddles.
• more good parallelism: I like rich desserts, fast card-games, and difficult riddles.

• bad: She is unfathomable, with a head of strawberry blond hair, and has a seductive manner.
• good: She is an unfathomable, seductive strawberry blond.

• bad: He is cute, wears a pinstriped suit, and has a dashing way about him.
• good: He is cute and dashing in his pinstriped suit.

• bad: The faun has shyness, with rough hooves, and behaves in a sylvan fashion.
• good: The faun is shy, rough-footed, and sylvan.
• good: The rough-hoofed faun is shy and sylvan.

Note that faulty parallelism isn't really a grammatical mistake. It's actually a stylistic problem. When editors are marking up a paper for revisions, you may note they place a pair of slanting lines in the margin--like this //. Those two slanting lines (//) indicate the editor has spotted faulty parallelism in that line of text, and the editor wants the author to fix it.