When is it okay to use 'not' when posing a question?
As I understand it, people add “not” to questions in this way for one of two reasons:
- The asker believed she knew the answer but now is unsure
- The asker knows the answer and is proving a point
In the first example, imagine a parent who instructed his child to finish her homework before playing video games. When arriving home, he finds his daughter playing some game and assumes that she finished her homework. Later, finding out that she did not do so, he might ask “Did you not finish your homework?” (perhaps an interrobang would be more suitable).
The second example seems far more common, since it occurs when most anyone feels the need to disguise their argument as a set of claims to be refuted by the answer. E.g., lawyers often seem to use such a construction because each answer that does not refute the claim appears to reinforce the asker's argument.
[How do you properly answer?]
As mentioned by @oerkelens and suspected by the OP, part of the confusion when answering these formulations is that English does not have a separation between affirmation and negation with “yes” (where the French and some other languages do).
However, there exists a very simple way to answer these questions unambiguously. Avoid using “yes” and “no”. Instead, only answer with the clarifying clause.
E.g., someones asks, “Are you not going to the parade?” The unambiguous affirmative would be “I am going to the parade,” whereas the unambiguous negative would be “I am not going to the parade.”
If you felt compelled to use “yes“ or “no“, you might choose which to say depending on the asker's expected reply. That is, if the answer is inline with what the asker expected, the answer would be “yes,” else “no.”
Expecting Marry to have gone to the store, Shelby asked, “Did you not go to the store?” Marry replied, “Yes, I went to the store.”
Unfortunately, with no emphasis or context around such formulations, it might be difficult to discern the asker's expected answer. As a result, I would recommend the simpler and unambiguous answer when possible.