Parallel lines in geometry always run in the same direction and are the same distance apart. Parallel lines (or sentences) in writing also have this sense of sameness and equidistance. Writing Well defines parallel construction as a sentence within which “phrases or clauses repeat the same word forms (nouns, verbs, adjectives) in the same order to perform the same function” (Hall and Birkerts 153). You should choose not only to repeat the same part of speech but also to use the same configuration of that part of speech (make all nouns plural, all verbs infinitives (“to ___”) or gerunds (“__-ing”), etc.)

Sentences that don’t contain parallel elements can look and sound sloppy or confusing:

  • I need to go to the bank, then I’ll shop for groceries, and tonight I planned on fixing dinner at the house.

In this example, each of the main verbs is in a different tense; although you can certainly have different tenses within a single sentence depending on content and context, here there is no clear reason to put one verb in the present, another in the future, and the last in the past—the verb forms are not parallel. Additionally, each of the verbs that describes further action to take place (going to the bank, shopping for groceries, and fixing dinner) takes a different form or appearance: “to go” is an infinitive, “shop” a single verb, and “fixing” a gerund.

You can fix both problems with parallelism in numerous ways; the following are only a few possibilities:

  • I’m going to the bank, shopping for groceries, and fixing dinner at the house.
    OR
  • I need to go to the bank, shop for groceries, and fix dinner at the house.
    OR
  • First, I’ll go to the bank; then, I’ll shop for groceries; finally, I’ll fix dinner.

Here is another example of a sentence with nonparallel elements:

  • Because of the academic stress and the way our immune systems get stressed during winter, college students need to be both hard workers and in good health to succeed.

“The academic stress” and “the way our immune systems get stressed” are both the objects of the word “Because”—both are explaining one of the reasons linked to this “because.” Since they are performing parallel functions in this sentence, they must be parallel in form:

  • Because of academic stress and immune-system stress…
  • Because of academic and immune-system stress…
  • Because of stress on our academic performance and on our health…

In the second part of the sentence, college students are advised to be both “hard workers” (a noun) and “in good health” (an adjective). To be parallel, both phrases should be the same part of speech:

  • …college students need to be both hard-working and healthy.
  • …college students need to be both hard workers and healthy individuals.