Sometimes this happens:

• Person 1: X?
• Person 2: No, because y.
• Person one hears: Yes, if not-y. (And then acts accordingly).

No-because doesn’t mean yes-if. It doesn’t necessarily give you all, or even any of the reasons the answer is no. Changing things so that the no-because no longer applies doesn’t automatically make the answer yes. All it gives you is some information that might be useful in asking another question.

Some more concrete examples:

• Hat-asker: Hey, can I borrow your hat?
• Hat-owner: No, it’s raining and I don’t want it to get wet.
• Hat-asker then assumes: If there’s no risk of getting the hat wet, then Person 2 agrees that it is ok for me to wear it.
• Hat-asker  borrows the hat without asking, but only wears it indoors.

In this example, it would probably be ok for Hat-Asker to ask Hat-Owner, “Actually, I just wanted to wear it for a minute in the other room to entertain my friend. Would that be ok?”, but it would not be ok to assume without asking that it would be ok because the hat definitely wouldn’t get rained on.

Or this:

• Person 1: Hey, let’s sit together
• Person 2: I’m really not in the mood for company; I want it to be quiet.
• Person 1 thinks: It’s ok if I sit there if I don’t make any noise. (And then sits next to Person 2 without verifying that this is ok).

In this situation, it might be ok to ask if it was ok to sit there quietly without having conversation, but it also might be better not to ask. (I’m not sure how to explain the difference, though.) But it would be invasive to just sit there and assume doing so quietly was ok.

Or this:

• Person 1: Hey, do you want to go out on a date?
• Person 2: No thanks; I’m too busy for dating this semester.
• Person 1 thinks:  Person 2 will go out with me during winter break.

In this case, it’s important to bear in mind that wanting to date someone doesn’t necessarily mean they want to date you, or that they should date you, or that they should consider dating you. No-because doesn’t mean yes-when. In this case, it would be probably ok to ask again when it gets to be around that time, but it would not be ok to assume that the answer will be yes, and it would not be ok to demand an explanation of why the answer is still no.

Because people have the right to say no to requests for favors, attention, and use of their possessions, and they don’t generally owe you an explanation.