Parallel Structure

both . . . and

not only . . . but also

either . . . or

neither . . . nor

These two-part conjunctions (called correlatives) are frequently used in academic writing. What’s tricky about them is that the same grammatical form (for example, two clauses, two nouns, two verbs, two prepositional phrases) must follow both parts of the conjunction.

Not parallel

Population growth not only [verb] threatens the developing nations but also [noun phrase] the rest of the world.

Parallel

Population growth threatens not only [noun phrase] the developing nations but also [noun phrase] the rest of the world.

Not parallel

Either [clause] we need to cut spending or [infinitive] to raise taxes.

Parallel

We need either [infinitive] to cut spending or [infinitive] to raise taxes.

or

Either [clause] we need to cut spending, or [clause] we need to raise taxes.