Explanatory の particle in question

Question

I've been watching a few videos and reading up on how the の particle is used in explanations (along with だ/です for statements) and I've come across this video.

It explains how you can use の for seeking explanations at the end of a question and how you can conjugate the の particle as a noun however I don't understand the nuance in the following questions:

If someone asks this question to me

学生じゃないの？

Or

学生なんじゃない?

My understanding is that the first one means "You're not a student?" But the latter I'm unsure about because I think it means the same thing as the first sentence.

As it stands , If I am not a student then I would reply

学生じゃないんだ

to both questions.

I asked my Japanese friend what is the difference and she told me that the first one is a negative question and the second one means "(S/he) is maybe a student." and that it's more of "guessing"

I'm quite confused by this given that the negative conjugation is used in the second sentence.

My question is what is the difference between those two sentences and what is the actual meaning?

Answer 1

「じゃない」 is much more complex than many Japanese-learners seem to think or even have actually been taught. That is because it is used both affirmatively and negatively (whereas some learners seem to think it is automatically negative because of the 「ない」).

For instance, if a native speaker said:

「うまいじゃない、このピザ！」 (「うまい」 means "tasty".)

that would mean "This pizza is yummy!" 100% of the time. It just could never mean "This pizza is not yummy." even if you wanted it to. Why not? Because the negative form of 「うまい」 is 「うまくない」 and not 「うまいじゃない」.

Though brief, What I said above is the absolute prerequisite for any further discussion regarding 「じゃない」.

Let us look at your examples now.

「学生{がくせい}じゃないの？」

This can mean two very different things depending on the intonation used.

1. "(Really?) You're not a student? (I thought you were.)" ← Negative 「じゃない」

2. "(Someone) is a student, right? (I am pretty sure s/he is.)" ← Affirmative 「じゃない」

「学生なんじゃない？」

can only mean one thing: Same as #2 above. It is the affirmative 「じゃない」.

One would need to have much experience speaking to native speakers to be comfortable with different usages of 「じゃない」 because a large part of it has to do with intonation. Part of it is just plain grammar so that one needs no speaking skills to tell the two types of 「じゃない」 apart.