Parallel structure is used to express matching ideas. It refers to the grammatical balance of a series of any of the following:
both . . . and
neither . . . nor
whether . . . or
either . . . or
not only . . . but also
NOTE: Correlative conjunctions must be used as pairs (not only with but also, not just but) and not mixed with other conjunctions such as neither with or.
Note: Repetition of prepositions is considered formal and is not necessary.