Rule: Assertive forms in questions indicate that positive answer is expected. Non-assertive forms in negative questions expect a negative answer. Assertive forms in negative questions strongly expect a positive answer.
Examples of errors:
(1) I never considered you dull because you're from the country. Does somebody of you feel any disadvantage because he was born or lived in the country?
(2) Some women think marriage is a kind of prostitution. That's a strange statement, but couldn't there be any truth in it?
Non-assertive forms (cf. 6.1) are normally used in questions, as well as-in negative clauses (and if clauses), for example:
I heard somebody at the door already (assertive)
I didn't hear anybody at the door yet (negative, non-assertive)
Nobody heard anybody at the door yet (negative, non-assertive)
Did he hear anybody at the door yet? (interrogative, non-assertive)
This rule can be purposely broken, however, in order to express the speaker's expectation of a positive or negative answer to his question. If the speaker's attitude is neutral, the non-assertive forms are used:
Is anyone at the door?
Is he here yet?
If he expects or anticipates a positive answer, he will use the assertive forms:
Is someone at the door?
Is John here already?
Here the speaker has some reason to believe that there is in fact someone at the door, and that John is already here.
This would be simple enough, except for the fact that there is another device that can be used with the same effect, namely negative questions. A negative question also shows that a positive answer is expected:
Is John here? (neutral)
Isn't John here? (positive answer expected)
When these two devices--the use of assertive instead of non-assertive forms and negation of the verb--are put together, the result is a question which indicates very strong expectation of a positive answer:
Isn't someone at the door?
= There is someone at the door, isn't there?
To complicate things still further, there is another possibility: a negative question with non-assertive forms, e.g.:
Isn't anyone at the door?
= There isn't anyone at the door, is there?
In this case, the answer "No" is expected, which has the effect of confirming a negative proposition, i.e. "No. there isn't anyone at the door." To summarize, there are four possible variations:
Is anyone at the door? (no expectation)
Is someone at the door? (expects positive answer: someone is there)
Isn't someone at the door? (strongly expects positive answer: someone is there)
Isn't anybody at the door? (expects negative answer: no one is there)
If the question is a tag, falling intonation also has the effect of emphasizing the expectation of the speaker, e.g.:
There is someone at the dòor, ísn't there? (expects positive answer)
There is someone at the dòor, ìsn't there (strongly expects positive answer)
There isn't anyone at the dòor, ís there (expects negative answer)
There isn't anyone at the dòor, ìs there? (strongly expects negative answer)
Now we are in a position to evaluate (1) and (2). (1) was spoken during a class discussion by someone who had been accused of thinking or saying that country people are dull. Since she was defending herself against this accusation, she certainly did not expect a positive answer. In fact, the question was meant to have a rhetorical effect equivalent to
Surely none of you feel any disadvantage because you were born in the country?
Since a positive answer is not expected, any is appropriate here. On the other hand, the author of (2) expects the answer:
Yes, there could be some truth in it.
She has (incorrectly) formulated the question as if she expected a negative answer, though, equivalent to Isn't there anybody at the door?