The usage expert Claire Kehrwald Cook describes the correlative conjunctions, both . . . and, either . . . or, and not only . . . but also, as “double connections” that “emphasize the correspondence between the word groups they introduce” (59). Their emphatic weight makes them a popular rhetorical device. For example, if I were to say that Cook’s “correspondence” lies not only in meaning but also in form, it would be with the intention to emphasize the second element as a crucial component of the pair. As we will see below, correspondence of form helps establish the parallel structure essential to these “double connections.” The correlative conjunctions will either define that structure, guiding reader comprehension, or knock it askew, sending readers down unintended roads.
In the clause “Cook’s ‘correspondence’ lies not only in meaning but also in form,” not only and but also link two matching prepositional phrases, in meaning and in form (relating them to the verb lies). Yet matching phrases alone do not guarantee parallel structure. Note as well Cook’s use of the word introduce. Correlative conjunctions must be positioned to introduce each element in turn; otherwise the parallel structure will be lost. Let’s look at correct and incorrect positioning of correlative conjunctions to introduce the elements of a pair:
This exercise will not only help students grasp the logic of sentence structure but also prepare them to detect errors.
Not only and but also introduce and thus define the two actions the exercise will perform: it will help students grasp the logic of sentence structure, and it will prepare them to detect errors. How would shifting even one of those positions affect the parallel structure? The following placement is common:
This exercise will help students not only grasp the logic of sentence structure but also prepare them to detect errors.
The sentence now purports to define two actions that the students, rather than the exercise, will perform. But there is only one such action in the sentence: students will grasp the logic of sentence structure. Students are the object of the second element, the “them” who will be prepared to detect errors; the action is performed upon them, so without further revisions to the sentence, they cannot perform it themselves. Because the pair cannot be completed as promised, readers must backtrack and reassemble the intended pair while carefully ignoring the writer’s misleading directions.
As Cook points out, such errors appear in print in “abundance” (56), often as a result of incomplete revision (59). The sentence above likely reflects an intermediary stage between the first example and this version:
This exercise will help students not only grasp the logic of sentence structure but also learn to detect errors.
The correlative conjunctions are still in the positions that disrupted the original parallel structure, but the sentence elements as revised (in which students both “grasp” and “learn”) now justify those positions, restoring the parallelism. Cook advises, “When you’re roughing out a first draft, the conjunctions may not fall where they belong . . . but be sure to put them right when you revise” (59). This may mean either moving the conjunctions themselves or revising the elements they define to correspond correctly. Either way, keep in mind that because correlative conjunctions define the elements you’re combining, they determine the meaning of your sentence. You can practice by taking our quiz.
Cook, Claire Kehrwald. Line by Line: How to Edit Your Own Writing. Houghton Mifflin, 1985.