What I understand about an "adverb" is that it modifies a verb. E.g. in 遅く走ります
, 遅く
is an adverb because it modifies the verb 走ります
. It "describes" how I run (slowly).
Now back to 皆...
One example of how it is used as an adverb is お茶を皆飲みます
. Sure, 皆
appears just before 飲みます
, but I don't really understand its function as an adverb. As in, I can't see how it (皆) modifies the verb. To me, it appears more like it is describing how much of the tea I drink, much like the function of 全部
in 全部のお茶を飲みます
. It's unlike the use of, say, 速く
in お茶を速く飲みます
. In this case, the adverb 速く
does describe the verb/action of drinking the tea (quickly).
What am I not understanding correctly?