The Essentials of Writing

The Hamilton College Style Sheet

Essentials of English Usage

Parallelism ("pl")

Sentence elements that are parallel in thought and function must be parallel in form.

Parallel elements in a sentence are two or more words, phrases, or clauses that occur together and have the same grammatical function and the same importance of thought.  Parallel structure, when used correctly, creates a symmetrical, graceful construction that is pleasing to the reader. Parallel structure used incorrectly can make writing appear sloppy and can confuse a reader.

1. Three reasons why steel companies keep losing money are that their plants are inefficient, high labor costs, and foreign competition is increasing.
[Ineffective: This sentence appears to argue that "their plants are ... high labor costs." Parallel clauses must maintain consistent form. Better: Three reasons steel companies keep losing money are inefficient plants, high labor costs, and increasing foreign competition.] 

2. They knew him to be a liar and that he would not keep his appointment.
[Ineffective: an and that clause must be preceded by a that clause. Better: They knew that he was a liar and that... Similarly, an and who clause must be preceded by a who (whose, whom) clause; an and which clause must be preceded by a which clause.] 

3. Bushes are shrubs; the Ford is a car, and an example of a beer is Sam Adams.
[Ineffective: This sentence illustrates three errors in parallelism.

a. The context here requires parallelism in number: A bush is...a Ford is...a beer is...
b. An example is not logically parallel with a shrub and a car.
c. The punctuation separating the elements in the series is not parallel (a semicolon would imply that the Ford is a car is an extension of the idea that bushes are shrubs).]