are there any concrete rules for using いっぱい　たくさん　and よく？


Of course I can use these but sometimes I am corrected by Japanese people when
I use them in the wrong circumstance.

For example,

  * 「よくしってるやん」 = "You know it quite well don't you!"
  * 「よくいきます」＝ "I go (there) a lot"
  * 「皿がたくさんあります」= there are a lot of plates 
  * 「人がいっぱいいる」= there are lots of people

Just wondering if anybody has any concrete rules that I can follow so that I
don't make any (or as many) mistakes in the future.




たくさん means that the quantity is large: “many,” “much,” and “a lot.” As Ignacio
Vazquez-Abrams said, いっぱい means “full,” but いっぱい is colloquially also used to
mean the same thing as たくさん. (In child-speak, they also mean that the degree
is high: 今日は(いっぱい/たくさん)遊んだね (you played a lot today).)

Adverb よく does not mean that the quantity is large. It means:

  * very much, when talking about degree (not quantity): よく知ってるやん is an example of this.
  * often: よく行きます is an example of this.

よく is also the continuative form of adjective よい/いい.

