Not sure if this belongs here, but a grammar quiz question (about casual present negative) had "食べられない" for "I can't eat [any more]". Is this correct? The internet says this might be a form that means "to be inedible"? Was this a goof in a user sentence?
It's a sentence that is probably a bit too high level for that quiz. It is not only this form, but also the potential form 食べられる - which means "to be able to eat/can eat" - so it does mean "can't eat", or "unable to eat" - it could mean that it is inedible, or perhaps something you cannot eat because of a personal choice or an allergy.
That being said, we are currently making a brand new batch of N5 quiz questions to better fit the difficulty level in the actual N5 test.
not sure if it belongs here but the lesson teaching about the casual form also mentioned だ and です.
regarding い adjectives it says that both です and だ *can* be dropped. This sounds misleading to me as all other sources I have seen say that it is wrong to couple い adjectives with だ since the い adjective already includes the "to be". です on the other hand is added purely to show politeness in this case and adds no meaning.
am I misinformed about this topic or is the explanation here shaky?
… say that it is wrong to couple い adjectives with だ since the い adjective already includes the "to be".
I would phrase this slightly differently. Since 形容詞 (い-adjectives) inflect, they are capable of embedding the copula, but that doesn’t mean that they must always embed the copula. The way I see it, appending です or だ effectively steals the copula, perhaps by inserting a null pronoun after the adjective and converting it from a phrasal adjective to a noun modifying adjective. This may be a recent shift in usage.
For things like job interviews and classroom lessons, you are probably better off sticking with standard usage, but don’t be surprised if you hear non-standard variants on the street.