Which sentence correctly uses parallel structure?
A sentence uses parallel structure correctly when every item in a list, pair or comparison takes the same grammatical form — all nouns, all -ing verbs, all full clauses. “She likes reading, writing and hiking” is parallel; “She likes reading, writing and to hike” is not, because the third item switches form.
What parallel structure actually means
Parallelism is a rule about form, not about meaning. When a sentence sets up a series — two items, three items, a comparison, a pair joined by “both … and” — the reader's ear locks onto the grammatical shape of the first item and expects the rest to match it. Break that expectation and the sentence trips, even when the meaning is perfectly clear.
This is why faulty parallelism is so hard to catch in your own writing: you know what you meant, so the sentence reads fine to you. It is also why exam questions love it. The test is mechanical — line the items up and check whether they share a form — which makes it exactly the sort of thing a checker can verify reliably.
Incorrect:
The job requires patience, focus, and being able to work alone.Correct: The job requires patience, focus, and independence.
Two nouns then a gerund phrase. Making the third item a noun repairs it.
Incorrect:
He wanted to finish the report, to call the client, and sending the invoice.Correct: He wanted to finish the report, call the client, and send the invoice.
Once the first infinitive is marked with “to”, the rest can drop it — but they must stay infinitives.
Incorrect:
She is not only a talented pianist but also composes music.Correct: She is not only a talented pianist but also a skilled composer.
Correlative pairs — not only/but also, either/or, both/and — must join matching forms.
Where parallelism breaks most often
Three constructions account for most faulty parallelism. Lists of three or more, where the last item drifts into a different form. Correlative conjunctions — “not only … but also”, “either … or”, “both … and”, “neither … nor” — where the phrase after the first half has to match the phrase after the second. And comparisons using “than” or “as”, where the two things being compared must be the same kind of thing.
Bulleted lists deserve special mention, because they break the rule constantly and nobody notices. If your first bullet starts with a verb, every bullet should start with a verb. If the first is a sentence fragment, they all should be. A list that mixes fragments and full sentences reads as carelessly assembled even to a reader who could not name the problem.
Incorrect:
Running a marathon is harder than a half.Correct: Running a marathon is harder than running a half.
The comparison was between an activity and a distance. Repeat the verb form.
How to test a sentence for parallelism
Split the sentence at the conjunction and read each item against the shared opening. “The job requires patience” — fine. “The job requires focus” — fine. “The job requires being able to work alone” — grammatical, but a different shape from the first two. That mismatch is the error.
For correlative pairs, cover everything before the first half of the pair and check that what follows each half is the same kind of phrase. For comparisons, ask whether the two things on either side of “than” belong to the same category — an activity compared to an activity, a person to a person.
Once you have found the odd item out, you have two repairs available: change it to match the others, or change the others to match it. Pick whichever produces the shorter sentence.
