What exactly is parallel structure? It’s simply the practice of using the same structures or forms multiple times: making sure the parts are parallel to each other. Parallel structure can be applied to a single sentence, a paragraph, or even multiple paragraphs. Compare the two following sentences:

• Yara loves running, to swim, and biking.
• Yara loves running, swimming, and biking.

Was the second sentence a smoother read than the first? The second sentence uses parallelism—all three verbs are gerunds—whereas in the first sentence two are gerunds and one is an infinitive. While the first sentence is technically correct, it’s easy to trip up over the mismatching items. The application of parallelism improves writing style and readability, and it makes sentences easier to process.

Compare the following examples:

• Lacking parallelism: “She likes cooking, jogging, and to read.”
• Parallel: “She likes cooking, jogging, and reading.”
• Parallel: “She likes to cook, jog, and read.”

Once again, the examples above combine gerunds and infinitives. To make them parallel, the sentences should be rewritten with just gerunds or just infinitives. Note that the nonparallel example, while inelegantly worded, is grammatically correct: “cooking,” “jogging,” and “to read” are all grammatically valid conclusions to “She likes.”

• Lacking parallelism: “The dog ran across the yard and jumped over the fence, and down the alley he sprinted.”
• Parallel: “The dog ran across the yard, jumped over the fence, and sprinted down the alley.”

The nonparallel example, is grammatically valid; “down the alley he sprinted” is an entirely separate clause. However, it is not parallel. You may find that the parallel example sounds much better to your ears.

Parallelism can also apply to names. If you’re writing a research paper that includes references to several different authors, you should be consistent in your references. For example, if you talk about Jane Goodall and Henry Harlow, you should say “Goodall and Harlow,” not “Jane and Harlow” or “Goodall and Henry.” This is something that would carry on through your entire paper: you should use the same mode of address for every person you mention.

You can also apply parallelism across a passage:

Manuel painted eight paintings in the last week. Jennifer sculpted five statues in the last month. Zama wrote fifteen songs in the last two months.

Each of the sentences in the preceding paragraph has the same structure: Name + -ed verb + number of things + in the past time period. When using parallelism across multiple sentences, be sure that you’re using it well. If you aren’t careful, you can stray into being repetitive. Unfortunately, really the only way to test this is by re-reading the passage and seeing if it “feels right.” While this test doesn’t have any rules to it, it can often help.

Rhetoric and Parallelism

Parallelism can also involve repeated words or repeated phrases. These uses are part of “rhetoric” (a field that focuses on persuading readers) Here are a few examples of repetition:

• “The inherent vice of capitalism is the unequal sharing of blessings; the inherent virtue of socialism is the equal sharing of miseries.” —Winston Churchill
• “Let every nation know, whether it wishes us well or ill, that we shall pay any price, bear any burden, meet any hardship, support any friend, oppose any foe to assure the survival and the success of liberty.” —John F. Kennedy
• “And that government of the people, by the people, for the people, shall not perish from the earth.” —Abraham Lincoln, Gettysburg Address

When used this way, parallelism makes your writing or speaking much stronger. These repeated phrases seem to bind the work together and make it more powerful—and more inspiring. This use of parallelism can be especially useful in writing conclusions of academic papers or in persuasive writing.