as long as と as far as

You can listen to the music as ( ) as you like.

この( )に　long が入るのか　far か？という問題。
答えはもちろんlong なんですが、
as long as = if というやつではなく
「好きなだけ長く」という文字通りの意味と考えるべきでしょうね。

As long as I live, I will never forgive you.
As far as I can see, there is no one.
As far as I know, he has no girl friend.

How long は時の長さですし
How far は空間的距離→程度・範囲です。

やはり　long や　far の文字通りの意味が残りますなぁ。