The problem with responding to negative statements is that there are two ways of responding to them:
- You can respond with respect to the underlying thought.
- You can respond with respect to the veracity of the speaker's statement.
When given the statement, "We are not buying a new car" I can respond with,
- "No" meaning, "No we're not buying a new car." - I am responding to the underlying thought. And when we agree with the underlying negative statement we show agreement with a similarly constructed negative.
- "No" meaning, "No, we are buying a new car." - I am responding with respect to the veracity of the statement and indicating that the statement is false- we are, in fact, buying a new car.
- "Yes" meaning, "Yes, you are correct we are not buying a new car" - I am responding with respect to the veracity of the statement and indicating that the statement is true - we are not buying a new car.
- "Yes" meaning, "Yes, we are [buying a new car]." - I am responding to the underlying thought and disagreeing or correcting the misunderstanding.
As can be seen here it is impossible to correctly interpret a one word, "yes/no" answer to a negative statement because it is ambiguous as to which way the respondent is answering. (Sometimes tone of voice and timing can help in spoken exchanges).
This is why native speakers, wishing to be as clear as possible, will often provide that second sentence with the appropriate elaboration. Or, if they don't, why questions like, "'No' we are or 'No' we aren't?" are often heard. (And similarly for "Yes").
What else can be done about it?
The questioner can also realize that they're setting themselves up for a possibly ambiguous answer and change the question:
- "Are we buying a new car?"
- "Did I hear that correctly? We are not buying a new car?"
(Of course this isn't foolproof because the respondent can still answer the second question and not the first.)
The respondent can respond with
- "You are correct" (We are not buying a new car)
- "That's right." (We are not buying a new car)
- "Actually, we are buying a new car." - 'Actually' is used to introduce a contradictory statement.
- Precede the statement with 'fortunately' or 'unfortunately' depending on the "goodness" of the result:
"Unfortunately, no, we have to keep the old one"
"Fortunately, no, they were able to fix the old one and it should last for several more years."