Some conjunctions combine with other words to form what are called correlative conjunctions. They always travel in pairs, joining various sentence elements that should be treated as grammatically equal.
She led the team not only in statistics but also by virtue of her enthusiasm.
Polonius said, "Neither a borrower nor a lender be."
Whether you win this race or lose it doesn't matter as long as you do your best.
Correlative conjunctions sometimes create problems in parallel form.
Here is a brief list of common correlative conjunctions.
both . . . and
not only . . . but also
not . . . but
either . . . or
neither . . . nor
whether . . . or
as . . . as
Correlative expressions (both, and; not, but; not only, but also; either, or; first, second, third; and the like) should be followed by the same grammatical construction. Many violations of this rule can be corrected by rearranging the sentence.
It was both a long ceremony and very tedious.
The ceremony was both long and tedious.
A time not for words, but action
A time not for words, but for action
Either you must grant his request or incur his ill will.
You must either grant his request or incur his ill will.
My objections are, first, the injustice of the measure; second, that it is unconstitutional.
My objections are, first, that the measure is unjust; second, that it is unconstitutional.
When making comparisons, the things you compare should be couched in parallel structures whenever that is possible and appropriate.