serve for与serve as有什么区别?

1.The box will serve for a seat.这只箱子能当个座儿.2.This box will have to serve for a table until the furniture arrives.在家具运来之前,这个箱子可以当桌子用.3.Studies serve for delight,for ornament,and for ability.读书可以得到乐趣,获得文采,学会本领.4.He plucked a branch of maple to serve for a walking stick.他采摘了一根枫树枝,想把它当手杖用.1.We found that birch bark could serve as paper.我们发现桦树皮可以作纸用.2.Such stories serve as a spur to children's imagination.这类故事能激发儿童的想像力.3.He volunteered to serve as the manager of our department store.他自荐当我们商场的经理.
4.This episode may serve as a paradigm.这一插曲可以充作典型例子.5.They drafted her to serve as their delegate.他们选她当代表.
很显然,有些情况下,二者是可以通用的.以下为个人看法：serve as “是作为什么直接使用”的意思； serve for “是起到什么作用”或者“在什么方面起到作用或作出贡献”

不是
serve as 是充当的意思
A serve as B A充当B或是A起B的作用
serve for 更多是有为了的意思