Parallel construction, (also called Parallelism and Parallel structure) means using the same pattern of words to show that two or more ideas have the same level of importance. This results in clearer and more consistent writing, which helps readers better understand your point.

Consider this famous quote from Winston Churchill:

“The inherent vice of capitalism is the unequal sharing of blessings; the inherent virtue of socialism is the equal sharing of miseries.”

Note Churchill’s use of the same construction in the second part of the sentence as in the first (“inherent vice of capitalism” matches “inherent virtue of socialism” and “is the unequal sharing of blessings” matches “is the equal sharing of miseries“).

If Churchill had said instead, “The inherent vice of capitalism is the unequal sharing of blessings; socialism’s inherent virtue is sharing miseries equally,” the sentence would be considered a faulty parallelism. The beginning clause sets up an expectation for the reader that a similar construction will follow; when it doesn’t, readers may be confused by the abrupt shift.

Parallel Structure Examples

Faulty parallelism

• • • “Science used to be taught by the textbook method, while now the laboratory method is used.” In this version, the first clause sets up an expectation that the second clause will be similarly constructed, but the writer changes the form, creating a faulty parallel; the writer essentially says, “Science used to be taught this way; now this way is used.”

Correction

• • • “Science used to be taught by the textbook method, while now it is taught by the laboratory method. In this version, the writer has revised the second clause to parallel the first, essentially saying, “Science used to be taught one way; now it is taught another way.”

Alternate correction

• • • “The textbook method was once used to teach science, while now the laboratory method is used.” In this version, the writer chose to change the first clause to parallel the second: “The textbook method was…” matches “the laboratory method is…”).

The following sections provide several instances with examples of where you should pay close attention to parallel construction:

Articles and Prepositions

• • • Articles (a, an, the) and prepositions (of, in, by, at, etc.) in a list should either be used only once or be repeated with each term, as shown in Table 8.7.1:

Correlative Expressions

• • • Correlative expressions should be followed by the same grammatical construction, as shown in Table 8.7.2 below. The following are examples of correlative expressions:

• • • • both requires an and;
      • not only requires a but also
      • either requires an or
      • neither requires a nor
      • first, second, third OR firstly, secondly, thirdly, etc.)

Comparisons

• • • Comparisons should also be put into parallel structures whenever possible and appropriate, as shown in Table 8.7.3:

*In the first corrected version above, the writer leaves off the noun income because the possessive wife’s refers back to ‘my income.’ This is called the noun understood.

Verb Forms

• • • Verb forms should be kept parallel whenever possible, as shown in Table 8.7.4:

Exercise: Identifying Parallel Construction 

Which of the following sentences is an example of a properly constructed parallel sentence?

Briefly explain how the sentence is parallel and how the others are not.

Additional Resources

• “Parallel Structure.” Purdue OWL.

• “Examples of Parallel Construction in Technical Writing,” from Study.com

*This page borrows from the following source: 
"Parallel Structure." CourseHero.com. Source link.