Sorry if this has been answered before or is obvious,
So I just studied the point でわなくて on the N3 deck and realized I didn’t really see a way to tell the difference between the N4 なくて. I see for the Verbs and [i] adjectives you add の, but for the [na] adjectives and nouns I don’t see anything like that. I see it says the two points are synonyms but they seem a little different in the “but” aspect. is the only way to tell if they’re different from the 2 words being used being antonyms? thanks in advance!
て just has a conjunctive function/meaning however in English we use a variety of conjuntive words instead of just one. So the because/and/but nuances are all contextual in Japanese but in an English translation normally only one of them sounds natural. If I say two opposite things then the implication of the conjunction is “but”. If I express some feeling then the implication of the conjuction is “because”, etc.
Unless I am being thick, in this case I would say the actual grammar (of ではなくて with a noun or noun phrase) is repeated between lessons but I guess the focus is different due to what nuance is needed for the respective JLPT levels. I think the N4 なくて is introduced in contrast to verb+ないで (I haven’t sat the N4 but I would imagine that is the kind of thing then ask about). Equally, the idea of なくて being a plain conjunction of a negation is a bit easier to understand than the idea of it meaning “but”. I would put this down to Bunpro using the JLPT as a framework rather than it being a general overall grammar guide. There are many grammar points that are essentially repeated throughout different levels but just with a slightly different usage or form.
On the topic of this grammar point though I will say that it is an extremely useful one when speaking if you don’t know or you forget a word. Let’s say you forget the word みかん then you can say something like なんというか、オレンジじゃなくて...小さいオレンジみたいな果物...(What’s it called? Not an orange but…the fruit that is like a small orange…) and the person you are speaking to will almost certainly say みかん. In context even just [noun/noun phrase]じゃなくて... is normally enough to prompt the person you are speaking with to provide you with the correct word. As someone who has a pretty trash active vocab this is something I say a lot.
In the N4 point (and), part A and B go hand in hand, they complement each other and both are true statements. In the N3 point (but), part A is not true but part B is.
Like in the example sentence (N4 point):
私の車は静かではなくてガソリンの減りも早い。
My car is not quiet, and runs out of gas quickly.
Here both A and B statements are deficiencies of the car.
In the N3 point, statement B supplants statement A.
今日は暇ではなくて忙しいです。
It’s not that I am bored today, but busy.
For nouns and na adjectives, the expressions of the two points appear identical but with verbs the linking structure is very different.