Use of Correlatives

Here is an excerpt from my book : Candid English Grammar, which will try to answer your query on the use of correlatives :

The two parts of a Correlative are meant for two alternatives or parts of a sentence. So, they should refer to equal alternatives. That is, the common words that refer to both alternatives must be placed before the first part of a Correlative. Let us explain with the help of some examples :

Wrong : He either can buy the shirt or the trousers.

Right : He can buy either the shirt or the trousers.

You can see that the words – he can buy - are common to both alternatives. But this rule does not apply to Articles and Prepositions; for example :

Wrong : He has bought the either chair or table.

Right : He has bought either the chair or the table.

In this example, the word - the - is common to both alternatives.

Now, look another example for the use of Preposition :

Wrong : He kept the book on either the table or the bed.

He kept the book either on the table or on the bed.

The Preposition – on – has more to do with the alternatives. However, if a Preposition has more to do with the Verb, it will occur before the first part of the Correlative; for example :

Wrong : The policeman looked either for the robber or for the stolen bag.

Right : The policeman looked for either the robber or the stolen bag.

In the case of Infinitives, to goes with the alternatives and not the Correlative :

Wrong : He climbed up the roof to not only have some fresh air but also fly a kite.

Right : He climbed up the roof not only to have some fresh air but also to fly a kite.