Correlative conjunctions as mentioned earlier are paired conjunctions, which means they do not come in single words. They come in the form of pairs of words: either … or; neither … nor; both … and; not only … but also, and whether … or. The correlative conjunctions connect two words, phrases or clauses.
When using either … or or neither … nor, ensure that the verb agrees with the subject that is closer to it. This means if the two subjects are singular the verb is singular, and the verb is plural if both subjects are plural. But if one subject is singular and the other one is plural, the verb can be singular or plural depending on the subject closer to it.
(For meaning of correlative conjunctions, see List 12 - Conjunctions.)
The words, phrases or clauses used with a correlative conjunction must be grammatically similar in structure
No: He often goes not only to swim but also diving.
(The first part is a verb to swim and the second part is a gerund diving.)
Yes: He often goes not only swimming but also diving.
Yes: He often goes not only to swim but also to dive.
No: I like the rainbow not only is it of different colours but also it curves.
(The first part uses a prepositional phrase of different colours while the second part uses a verb curves. It will be correct to have both parts grammatically parallel.)
Yes: I like the rainbow not only is it of different colours but also it is of curved shape.
(Now both are prepositional phrases: of different colours and of curved shape.)
Error to avoid
No: I couldn’t go neither by bus nor by train.
(Neither is a negative word. It’s wrong to add another negative word couldn’t. Two negative words make the sentence positive.)
Yes: I could go neither by bus nor by train.