Parallel Structure: Why Some Lists Read Smoothly and Others Do Not
One of these reads well and one does not:
- She likes swimming, running and to cycle.
- She likes swimming, running and cycling.
The first is grammatical. It still trips the reader, because two items are -ing forms and the third is an infinitive. The pattern was established and then broken.
The rule
Items joined by and, or, or but must share the same grammatical form.
Nouns with nouns, verbs with verbs, clauses with clauses. The reader builds an expectation from the first item, and every subsequent one either meets it or jars.
Where it breaks most
Bulleted lists. The most common failure, because the items are written at different times:
- Broken: improve efficiency / cost reduction / we will increase sales
- Fixed: improve efficiency / reduce costs / increase sales
Paired conjunctions. Not only … but also, either … or, both … and require matching structures on each side:
- Broken: She not only writes well but also a good editor.
- Fixed: She is not only a good writer but also a good editor.
The test: cover everything from the second half and check the first half reads correctly on its own. Then do the reverse.
Comparisons. Both sides of than or as must match:
- Broken: Writing a report is harder than to give a presentation.
- Fixed: Writing a report is harder than giving a presentation.
The repeated word
With a series of prepositional phrases or infinitives, either repeat the leading word every time or use it once. Do not do it twice out of three:
- Awkward: to plan, to build and design
- Fixed: to plan, to build and to design
- Also fixed: to plan, build and design
Why it matters beyond tidiness
Parallel structure is what makes memorable sentences memorable. Almost every famous line in English rhetoric is built on it — three matching clauses, or two balanced halves. Break the pattern and the line collapses.
It is also a comprehension aid. In a list of six technical items, matching structure lets the reader parse each one with the pattern they have already built. Mixed structure makes them start again every time.
The check
Read your list items down the column, each one attached to the stem, ignoring the others. If any of them does not fit the stem, that is the broken one.
Checked against Merriam-Webster, the Chicago Manual of Style and the AP Stylebook. Spotted an error? Tell us — see our editorial policy.
