Here's why:
* Predicate Nominative: A noun or pronoun that renames or identifies the subject of the sentence. It is usually found after a linking verb.
* Linking Verb: Connects the subject of a sentence to a noun or pronoun that renames or describes the subject. Common linking verbs include "be," "seem," "appear," "become," "feel," "look," "sound," "smell," "taste," and "remain."
* Action Verb: Describes an action performed by the subject.
Example:
* Correct: She is a doctor. ("Is" is a linking verb, and "doctor" renames the subject "she")
* Incorrect: She runs a marathon. ("Runs" is an action verb; "marathon" is the object of the verb)
In summary:
* A predicate nominative *must* follow a linking verb to rename or identify the subject.
* A predicate nominative cannot follow an action verb.