^ Isn't it a rule in the structure of the tag question, for the verb to be negated and in the abbreviated form?
NOT A TEACHER
(1) All the posters have given us really useful information.
(2) As the moderator said, there is no 100% rule that the tag question has to be negated or in abbreviated (contracted form).
(3) Tag questions are NOT an easy matter. Some scholars say that they are
still trying to understand completely the subject of tag questions.
(4) For example, you could say:
(a) It is obvious,
isn't it?
(b) It is obvious,
is it not?
(c) It is obvious,
is it?
(4a) is probably the most common form.
(4b) is very formal; some people would use it for special emphasis (strength). (For example, one source on the Internet reminded me that judges and lawyers in court often speak like this: It is obvious that you are guilty,
is it not! Tell the truth to the court, and you will receive a lighter prison term!)
(4c) is not used very often. You use it when you are not asking a question. You
are really ageeing with what the other person said:
Tom: You love me.
Mona: It is obvious, is it! (I have been trying to hide my love for you. I guess that I did a bad job, for my love is so obvious to you.)
Sometimes, you use it when you want to be sarcastic (rude):
The Parser: I am a native speaker.
Martha: You are a native speaker, are you! Well, then, why don't you know more about English grammar! I think that some learners know more grammar than you do, Mr. Native Speaker!