[violation of parallelism with correlative conjunctions] As you can see, faulty parallelism--or a breakdown in parallel structure--happens when a pair or series of co-ordinating units (nouns, ...

DISCUSSED in the preceding five chapters were the consistent use of parallel structures as key to writing more readable, more ...

In grammatical terms, "not only" and "but also" are correlative conjunctions, stablemates of "both ... and" and "either ... or." They make the connection between two parallel elements of a sentence.