Parallel structure means using the same pattern of words to show that two or more ideas have the same level of importance. When your grammar matches your meaning, your writing flows naturally. When it doesn't, sentences feel clumsy and awkward.
Getting parallel structure right comes down to matching verb forms, infinitives, gerunds, and clauses in lists or comparisons. If you start a list with an action verb, every other item in that list needs an action verb in the exact same tense.
What is Parallel Structure?
At its core, parallelism is about balance. Think of a sentence like a mechanical scale. If one side holds a noun, the other side should hold a noun. If one side uses a gerund ending in -ing, the matching side should do the same.
Consider this unbalanced sentence:
- Incorrect: She likes hiking, swimming, and to ride bicycles.
The mismatch breaks the rhythm. Two items use gerunds, while the final item uses an infinitive. Fixing it is simple:
- Correct: She likes hiking, swimming, and cycling.
Now every item uses the exact same grammatical form. The sentence reads smoothly and delivers its point without friction.
Core Rules for Correct Sentences
Writers usually break parallelism in three common areas: items in a series, comparisons using than or as, and elements joined by coordinating conjunctions.
Lists and Series
When you write a series of three or more items, link them with coordinating conjunctions like and or or. Every item must share the same part of speech and grammatical structure.
- Incorrect: The candidate promised to lower taxes, creating jobs, and better schools.
- Correct: The candidate promised to lower taxes, create jobs, and improve schools.
In the corrected version, every item in the series follows the infinitive marker to (implied for the second and third items after the initial auxiliary verb structure).
Comparisons
Comparisons often pit two ideas against each other using than or as. If the structures on either side of the comparison don't match, the sentence sounds jarring.
- Incorrect: Running a marathon takes more endurance than to swim across a lake.
- Correct: Running a marathon takes more endurance than swimming across a lake.
Because the first element uses the gerund running, the second element must use the gerund swimming instead of the infinitive to swim.
Correlative Conjunctions
Correlative conjunctions—such as either/or, neither/nor, not only/but also, and both/and—require strict parallelism. Whatever grammatical structure follows the first conjunction must match the structure following the second conjunction.
- Incorrect: He wanted not only to pass the exam but also getting a high score.
- Correct: He wanted not only to pass the exam but also to get a high score.
Placing the infinitive phrase to pass after not only means you must place a matching infinitive phrase to get after but also.
Common Mistakes to Avoid
Even experienced writers slip up when sentence structures grow long or complex. Watch out for these frequent traps.
Mixed Verb Tenses
Jumping between past, present, and future tenses within a single coordinated clause destroys parallel flow.
- Incorrect: The manager reviewed the budget, checks the inventory, and will approve the schedule.
- Correct: The manager reviewed the budget, checked the inventory, and approved the schedule.
Keep your verb tenses consistent unless the context of time explicitly requires a shift.
Changing Voices
Mixing active and passive voice in a compound sentence creates awkward phrasing.
- Incorrect: The committee discussed the proposal, and a final vote was taken by the members.
- Correct: The committee discussed the proposal and took a final vote.
Keeping both verbs active makes the sentence punchy and direct. For style guidelines and academic standards, you can consult resources like the Purdue Online Writing Lab or the Chicago Manual of Style.
Frequently Asked Questions
How do I check if a sentence is parallel?
Read the sentence aloud, focusing specifically on lists, bullet points, or comparisons. Break the sentence down into its individual components. If one part sounds like a gerund while another sounds like an infinitive or a complete clause, rewrite them so they share identical grammatical roots.
Does parallel structure apply to bulleted lists?
Yes. Bullet points are simply vertical lists, and they must follow the exact same parallel rules as sentences written in a paragraph. If your first bullet point starts with a verb, every other bullet point in that list should start with a verb in the same tense and voice.
Are there exceptions where non-parallel structure is acceptable?
In creative writing, authors sometimes break grammatical rules for stylistic effect, rhythm, or emphasis. However, in professional, technical, academic, and business writing, maintaining strict parallel structure is mandatory for clarity and professional polish.
