How do these two carry nuances of meaning: "Давай узнаем, не ... ли ..." vs. "Давай узнаем, ... ли ..."?

Question

Давай узнаем, не вернулись ли остальные.

{vs}: Давай узнаем, вернулись ли остальные.

I wonder if the first version with "не" is working on the assumption that they're probably already back, whereas the second suggests a slim chance of their return? My assumptions:

не ... ли: They are likely to be already back. But let's find out for sure, just in case they aren't.

ли: I don't think they're back yet. But let's check it out anyway on the off chance.

Incidentally, can you think of other examples where "не ... ли" and "ли" make a difference like this?

Answer 1

I'd (a native speaker obviously) say that the only difference I feel is "не … ли" is more colloquial. Without "не" this is perfectly suitable for an article, e.g. "Важно ли знать правила русского языка?" - with "не" this would read rather strange.

Maaaybe with "не" the speaker (again, colloquial usage) implies that they sort of hope/expect/think the event more likely, but again, the difference in meaning is negligible compared to the difference in the sense of colloquiality.

Answer 2

The difference is very subtle and also may depend on context. As a rule of thumb I'd suggest using the version without не in all declarative sentences. The negation adds some peculiarity which may be hard to capture.

For the given example I'd say that вернулись ли остальные doesn't necessarily implies slim chance. It can as well mean that you have solid grounds to expect they are going to return. But the expression is neutral.

The version with negation on the contrary shows that you are looking forward for the return. This also makes the expression sound conversationally.

In other contexts не + ли may express other nuances. For example, it may add extra politeness to your offer as in "Не хотите ли чаю?" And when making a polite request this не becomes mandatory as in "Не найдется ли у вас листа бумаги?"