How to differentiate when に is a target vs. an adverb


先生が来たらみな静かになった

I understand that 静か is a noun

Will this ALWAYS mean quietly or is it a target, for example

私は静かに友人に手紙を出しました, i quietly gave a letter to a friend, i understand it means
quietly, making it 静かに and target is 友人に

but for this example

みな静かになった, is this a target or an adverb? I know its super basic but something
that still confuses me, thanks in advance!




I think considering how a descriptor word like 「静か」 could operate as a target
would be helpful to consider. This word is not a person, place, thing, idea
etc. Instead, it is a descriptor word. I would call 静か a な-adj or an
adjectival noun, so when に is used is is always pretty safe to say it is used
as an adverb vs. a target of an action. You can't give a letter to "quiet",
you can't go to "quiet", you can't ask a question to "quiet."

Now for 静かになった I _guess_ you could see it as both a adverb and a target, but
not in the same sense as the sentence you presented about a letter. This
grammar construct uses the form ~になった if ~ is a な-adj or a noun, but uses
~くなった where ~く is the adverb form of an い-adj (aka adjectival verb). So while
the English translation "Everyone became quiet" doesn't use "quietly" I would
say it is safe to see 静かに as an adverb.

