Chances are you’ve been told at least once by an editor, a teacher, or another writer that “this construction isn’t parallel.” Or someone has scrawled “faulty parallelism” in the margin of your manuscript or in a comment on your Word file.

This is shorthand for straying from, as Words Into Type puts it, “the principle that parts of a sentence that are parallel in meaning should be parallel in structure.”

Faulty parallelism comes in an daunting array of varieties. It can involve nouns, verbs, phrases, clauses, and whole sentences. It’s easiest to spot in a list, like this one:

These tips might help you complete a long writing project:

• Schedule a specific time for writing.
• Write even when you don’t feel inspired.
• No distractions.

The first two elements are imperative verbs. The third has no verb at all. This is an easy fix: make the third element parallel to the first two by adding a verb. “Avoid distractions”? “Ignore distractions”? “Resist distractions”? It’s your call.

Faulty parallelism can be harder to spot in a sentence, especially a long, complex sentence — which is exactly where parallelism tends to go off the rails, so to speak. The list above can be turned into a sentence: “To complete a long writing project, schedule a specific time for writing, write even if you don’t feel inspired, and no distractions.” The sentence is short enough to make it pretty clear that something’s wrong.

The longer the sentence, the harder it can be to keep track of its parts. Here’s where the ability to diagram sentences can be very helpful. If you didn’t learn it in school or have forgotten how, plenty of websites out there can give you the basics, including “How to Diagram Sentences” on WikiHow.

It happens often enough that the parallelism is faulty but the meaning is still clear. I encounter many sentences like this one: “She let the dog in, gave him his supper, and then they went for a walk.” It sets off to be a series of three verbs with the subject “she,” but then the subject changes. What we’ve actually got here is two independent clauses, the first of which has two verbs, the second of which has one: “She let the dog in and gave him his supper, and then they went for a walk.”

I sometimes feel a little pedantic inserting the conjunction, because the meaning is clear, but often enough the meaning isn’t clear, or the sentence can be interpreted in more than one way. The other day I came across a doozy in a nonfiction book I’m copyediting. In this example, I’ve changed the details but retained the structure of the original. The original subject was a man who never wrote a best-selling novel and didn’t go to Spain either.

Mindy Moore had not begun to think about traveling to Spain, still less write her best-selling novel.

See the problem? There are three verbs in the first part of the sentence — “begun,” “think,” and “traveling” — and it’s not obvious which one “write” is meant to be parallel with. Keeping in mind that even very good writers occasionally mess up our verb tenses, you could read this in (at least) three ways, some of which might not be accurate.

• Mindy Moore had not begun to think about traveling to Spain, still less written her best-selling novel. (“Written” is parallel with “begun”: “Mindy had not begun . . . and had not written . . .” If this were the intended meaning, I would probably insert “yet” before “begun” to make it even clearer.)
• Mindy Moore had not begun to think about traveling to Spain, still less to write her best-selling novel. (“To write” is parallel with “to think,” meaning that Mindy hadn’t begun either to write her best-selling novel or to think about traveling to Spain.)
• Mindy Moore had not begun to think about traveling to Spain, still less about writing her best-selling novel. (“Writing” is parallel to “traveling,” meaning that Mindy hadn’t even begun to think about writing her best-selling novel.)

Context gave me no clue about which of the three options was intended, but my gut said it was probably #2 because it was the easiest to clarify: add the “to” to show that “to write” was an infinitive and therefore parallel with “to think.” So I added the “to,” but I also queried the author and explained the other options. He’s the only one who knows for sure what he intended and what was in the subject’s head.

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