Hi saeiiiid, In "John is a student", "is" is a linking verb which actually connects the subject (John) to its predicate nominative (a student). A linking verb does not express an action, unlike other verbs such as "learn" or "do". Instead, it describes a quality or state of a subject. In turn, a predicate nominative completes a linking verb and provides more information about the subject. In your sentence, the predicate nominative (i.e. a student) provides more information about who the subject (i.e. John) is. As a side discussion, take a look at these two sentences below: 1. He fails badly. (grammatically correct) "fails" is a verb describing an action; "He" describes the subject doing the action; "badly" is an adverb of manner showing how he failed. However, we do not write: 2. He feels badly. (grammatically wrong) This is because "feel" is another linking verb. "feel" does not describe an action although it is a verb; instead, it describes the state of mind of a person. The sentence should be written as "He feels bad." (Subject--> He / Linking verb --> feels / "bad" --> predicate adjective (since it describes the subject)) I hope this helps.

Yes, 'a student' is the object of the sentence. Objects often answer the question 'what'. What is John? John is a student.

What a strange question for an English teacher to ask.

You need to study subject and predicate. http://www.myschoolhouse.com/courses/O/1/55.asp

Why do you think the names of grammatical things are important?.. just wondering?