How to identify the head noun in a noun phrase or clause?

How to identify the head noun in a noun phrase or clause?

A common problem a copyeditor faces is the identification of the right subject for the verb. As easy as it seems, even careful copyeditors may fail to recognize the lack of agreement between a subject and its verb because of the intervening phrases and clauses. By systematically approaching the subject phrase, we can identify the head noun of a noun phrase easily as explained in this post.