Section 18.6 Parallel Structure
Coordination is one of the basic operations in grammar: joining elements at the same level with conjunctions like and, but, and or. The key word is same level. Coordination works because both elements belong to the same grammatical category—noun with noun, verb with verb, clause with clause. When you coordinate elements that are not the same category, the structure breaks, and the reader feels the mismatch even without being able to name it.
Coordinated elements should be grammatically parallel. Faulty parallelism occurs when coordinated items are not in the same grammatical form.
Faulty Parallelism.
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She likes swimming, hiking, and to ride bikes. -
Clear: She likes swimming, hiking, and biking.
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The proposal is interesting, innovative, and has potential. -
Clear: The proposal is interesting, innovative, and promising.
With Correlative Conjunctions.
Parallel structure is especially important with correlative conjunctions (both...and, either...or, not only...but also):
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She not only plays piano but also she sings. -
Clear: She not only plays piano but also sings.
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Either you leave now or staying late. -
Clear: Either you leave now or you stay late.
