Parallel structure matters in pairs too. Correlative conjunctions come in pairs: both … and, either … or, neither … nor, not only … but also, whether … or. Whatever follows the first word must match what follows the second.
Key idea
Put each half of a correlative pair right before matching words: noun with noun, verb with verb, phrase with phrase. In comparisons with than or as, compare like with like.
Why it works
A pair works like a balance scale: each pan must hold the same kind of thing. Strunk wrote in 1918 that correlative expressions “should be followed by the same grammatical construction.”
Worked example: Move the first half
“She not only plays the piano but also the violin.”
- After not only: plays the piano, a verb phrase.
- After but also: the violin, a noun.
- Move not only so a noun follows it too.
Answer: She plays not only the piano but also the violin.
Worked example: Either … or
“Either you can walk or take the bus.”
- After either: you can walk, a whole clause.
- After or: take the bus, a verb phrase.
- Move either next to the verb.
Answer: You can either walk or take the bus.
Worked example: A comparison
“Ana’s grades are higher than Ben.”
- The sentence compares grades with … Ben himself.
- Compare grades with grades.
Answer: Ana’s grades are higher than Ben’s.
Common mistake
Putting the first half of the pair too early, as in “She not only plays the piano but also the violin.” Find the two halves and read what comes right after each; the two must match. In comparisons, check that you compare the same kinds of things: “Swimming is harder than running,” not “than to run.”