Careful writers use parallel construction.
Good parallelism means every item in a series is structured the same way. Whether the items are words, phrases, or dependent clauses, the elements in the list must match each other.
Parallel structure helps give a sentence unity and clarify its meaning. The parallel elements in a sentence help readers understand the relationship among the items in a series. Faulty constructions can cause readers to stumble.
The rule also applies for a bulleted list in a presentation. For example, if one bullet point begins with a verb, every bullet point should begin with a verb.
Here’s an example of parallel construction:
“that all men are created equal; that they are endowed by their creator with certain inalienable rights; that among these are life, liberty, and the pursuit of happiness.”
Every clause in the example serves the same function. Every clause is a grammatical match. The syntax works. (The third clause contains a list of three nouns; that’s parallel, too.)
The difference between parallel and dissonant is easy to recognize in this simple series:
(Faulty) I enjoy hiking, kayaking, and to garden.
(Parallel) I enjoy hiking, kayaking, and gardening.
The problem might be less obvious in this announcement that I edited several years ago:
is pleased to announce
new addresses, telephone and fax numbers
for our associates
The three items in the list as written lacked parallel structure. “Numbers” was intended to apply to telephone and fax, but not addresses. The sentence had to be corrected to say either:
new addresses and new telephone and fax numbers
new addresses, telephone numbers, and fax numbers.
Another frequent example of faulty parallelism is in sentences using “both . . . and.” The element after “both” and the element after “and” must be equivalent.
(Faulty) The journalism student aimed to both become a thorough reporter and a strong writer.
(Parallel) The journalism student aimed to become both a thorough reporter and a strong writer.
“Either . . . or” and “neither . . . nor” must be followed by equivalent elements, too.
Many writers have trouble keeping elements parallel, but it’s worth learning to do better. Readers will appreciate the effort.
The readers of this major newspaper deserved parallel structure on its special section’s front.