Parallel Structure
Learn how to keep items in a list, comparison or pair in a matching grammatical form, and how to recognize when a sentence has fallen out of balance.
Keeping items in balance
Parallel structure means matching items use the same grammatical form.
Parallel structure means using the same grammatical form for items that are joined together, whether they appear in a list, a comparison, or a pair connected by a conjunction.
In the sentence She enjoys reading, writing, and painting., each item in the list uses the same -ing form. If one item used a different form, such as reading, writing, and to paint, the sentence would no longer be balanced.
This page covers parallel structure in lists, with correlative conjunctions, and in comparisons, along with how to recognize and correct a sentence that has fallen out of balance.
The central idea
A single mismatched item breaks the pattern of the sentence.
Compare a balanced list with one that mixes different grammatical forms.
01
Balanced
Every item uses the same grammatical form.
He likes to run, to swim, and to cycle.
02
Unbalanced
One item breaks the pattern set by the others.
He likes to run, to swim, and cycling.
The useful question is: does every item match the pattern set by the first?
Once a list, comparison or pair begins with a particular grammatical form, every item that follows is expected to use that same form.
Parallel lists
Every item in a list should share the same form.
Matching -ing forms
She enjoys reading, writing, and painting.
Matching infinitives
The plan is to research, to design, and to build.
Matching nouns
The kit includes a hammer, a drill, and a saw.
Parallel structure with correlative conjunctions
Each half of a matched pair needs the same form.
Correlative conjunctions, such as either…or and not only…but also, join two parts that are expected to match grammatically.
Matching verbs
She either calls or emails her clients.
Matching nouns
She is not only a teacher but also a writer.
Parallel structure in comparisons
The two sides of a comparison also need to match.
Walking to work is healthier than driving.
Both sides of the comparison use the same -ing form. Comparing walking with to drive would break the pattern, even though the sentence would still communicate a similar idea.
A practical decision guide
Ask these questions when a sentence contains multiple items.
01
What form does the first item use?
Identify whether it is a noun, an -ing form, or an infinitive.
02
Does every other item use that same form?
Check each item in the list or pair against the first.
03
Are two items being compared?
Confirm both sides of the comparison share the same grammatical form.
04
Is a correlative conjunction being used?
Check that the word or phrase following each part of the pair matches.
Common errors
Mistakes are useful when you understand why they happen.
He likes to run, to swim, and cycling.
He likes to run, to swim, and to cycle.
The first two items use the infinitive form, so the third item should match it.
The report was clear, concise, and had good organization.
The report was clear, concise, and well organized.
The first two items are adjectives; the third should be an adjective too, not a separate clause.
She is not only a teacher but also writing books.
She is not only a teacher but also a writer.
Both parts of the correlative pair should use a noun, matching the form set by the first part.
Reading a book is more relaxing than to watch television.
Reading a book is more relaxing than watching television.
Both sides of a comparison should use the same grammatical form.
Your turn
Practise identifying and correcting parallel structure.
These activities are part of the learning process. There are no scores, no grades and no limit on how many times you may try.
Which sentence uses parallel structure correctly?
✅ Exactly! All three items use the -ing form.
❎ Not quite. The first two items are -ing forms, so the third should match.
What form do the first two items in the list use?
Which sentence keeps the correlative pair balanced?
✅ Exactly! Both parts of the pair use an adjective.
❎ Not quite. The first part uses an adjective, so the second part should too.
What kind of word follows “both”?
Which comparison is parallel?
✅ Exactly! Both sides of the comparison use the -ing form.
❎ Not quite. Check what form the first half of the comparison uses.
What form does “swimming” use?
Quick review
Matching items keep a sentence balanced.
Parallel structure means using the same grammatical form for items joined together in a list, a pair, or a comparison.
In a list, every item should share the same form, whether that is an -ing word, an infinitive, or a noun.
With correlative conjunctions, such as either…or and not only…but also, each part of the pair should match.
In a comparison, both sides should use the same grammatical form.
Remember
Check the first item, then measure everything else against it.
The first item in a list, pair or comparison sets the pattern. Every item that follows should be checked against that same pattern before the sentence is considered finished.