They are defined as mechanisms that link only two balanced words, phrases, and clauses. The linked elements should be parallel or equal in terms of length and grammatical similarity.
When two subjects are connected with a correlative conjunction, the second must agree with the following verb.
Every single evening either the horned owl or the squabbling cats wake Sam with their racket. Every single evening either the squabbling cats or the horned owl wakes Sam with their racket.
In the case of pronouns, the second antecedent must agree with the following pronoun.
Neither Yolanda nor the cousins expressed their disappointment when blind Aunt Sophie set down the plate of burnt hamburgers. Neither the cousins nor Yolanda expressed her disappointment when blind Aunt Sophie set down the plate of burnt hamburgers.
Primary correlative conjunctions in English:
both . . . and
"It is difficult to produce a television documentary that is both incisive and probing when every twelve minutes one is interrupted by twelve dancing rabbits singing about toilet paper." (Rod Serling)
either . . . or
Either John or George must have done this mischief.
neither . . . nor
"In nature there are neither rewards nor punishments; there are only consequences." (Robert G. Ingersoll)
not . . . but
"In the end, we will remember not the words of our enemies but the silence of our friends." (Martin Luther King, Jr.)
not only . . . but also
The Great Wall of China is not only up to 30 feet high and 32 feet thick, but also 1,400 miles long.
Other pairs which can be used:
as . . . as
If you are as intelligent as your father, it will not be difficult for you to run your family business.
just as . . . so
Just as the holiday's basis changed from a historical to a mythological one, so too is it now changing to become more political than anything else.
the more . . . the less
The more he eats, the...