The rule in one line
Items joined by and, or, but, or a comparison must occupy the same grammatical slot. All nouns, all verbs, all gerunds or all clauses: the form matters more than the length of each item.
Lists
A list breaks when one item changes shape.
| Not parallel | Why | Parallel |
|---|---|---|
| The job needs patience, accuracy, and working quickly. | Two nouns and one gerund phrase. | The job needs patience, accuracy, and speed. |
| The course teaches you to plan, drafting, and how to revise. | Infinitive, gerund, then a clause. | The course teaches you to plan, to draft, and to revise. |
| We walked to the station, bought tickets, and the train was boarded. | Two active verbs and one passive clause. | We walked to the station, bought tickets, and boarded the train. |
Comparisons
A comparison joins two things, so both sides must use the same form.
Cycling to work is faster than to take the bus. Cycling to work is faster than taking the bus.
The new version is easier to install and it also runs faster than the old one did. The new version is easier to install and faster to run than the old one.
The pattern to check is as ... as and than: whatever follows must match whatever precedes.
Paired conjunctions
Correlative pairs need the same form on both sides of the pair.
either ... or: Either you finish today or tomorrow is fine. Either you finish today or you finish tomorrow.not only ... but also: She not only writes novels but also poetry is written by her. She writes not only novels but also poetry.neither ... nor: Neither the price nor how long it takes was acceptable. Neither the price nor the delivery time was acceptable.
Why it matters
Parallel items are easier to scan because the reader learns one pattern and reuses it. A broken pattern costs a moment of re-reading while the reader works out which item changed shape. In a short email that moment is small. In a report with a long list it is the difference between a clear set of steps and a set the reader has to decode.
A quick test
- Find the list or the comparison.
- Underline the first item and name its form: noun, verb, gerund, infinitive or clause.
- Name the form of every other item.
- If one item differs, rewrite that item into the form of the first.
If the first item is awkward in a shared form, rewrite the whole list. Consistency matters more than which form you pick.
Check a sentence
The parallel structure checker marks the uneven item in a list or comparison, explains the rule it breaks and suggests a matching form.
Open the parallel structure checker