"c'est bien" vs. "c'est bon"
In the lesson "Subj. Present" I was given a sentence "It is good that you are living here" to translate. I wrote "C'est bon que vous vivez ici". I was told that was not correct, and that the correct translation was "C'est bien que tu vives ici".
Someone wrote in comments that "C'est bon" is wrong because "C'est" must be followed by an adverb (bien). But then what should I make of the famous song "C'est si bon"? I thought if the lyricist André Hornez repeated these words so many times in the song, then I could use them, too.
It turns out that there is another song by Charles Trenet named "C'est bon". How come?
Even if you used "bien", your sentence would be incorrect because you didn't use the subjonctive.
"C'est bien que vous vivez ici"/"C'est bien que tu vis ici" are incorrect.
"C'est bien que vous viviez ici"/"C'est bien que tu vives ici" are correct.
However, even if you used the subjonctive it would be incorrect -- or at least very weird -- to use "bon" here, simply because "bon" and "bien" don't have the same meaning. "Good" in English covers meanings that are separated in French (although in some cases they overlap a bit).
"C'est bon" can mean "It is tasty/pleasurable" (meaning used in the song "C'est si bon") or "It's all right". More rarely "il est bon" can be used to qualify someone/something that is virtuous.
"C'est bien" means that you are giving your favorable opinion on something. "It is appropriate/just/etc."
You'll notice that in both cases "It is good" is a fitting translation in English, however the meaning behind "good" shifts a bit.
But then what should I make of the famous song "C'est si bon"?
'Si' is an adverb and 'bon' is an adjective in this case, so the rule seems to be being followed.
I'm not sure about the other song.