as和for表示“作为”时的区别?

as,for表“作为、当作”
1.下列情况,二者可以通用.
①与build,serve,use等词连用表示用途时.如：
The house was built as (或for) a library.这房子是建作图书馆的.
The room serves as (或for)a meeting-room.这房间是用作会议室的.
This piece of wood can be used as(或for) a bookcase.这块木板可用来做书橱.
②与elect,choose等词连用,引出主语或宾语的补足语.如：
They chose him as (或for)their leader.他们选他为他们的领导.
Both of them were elected as (或for)the representatives to the meeting
他俩都被选为出席会议的代表.
2.下列情况下只能用as,不能用for.
①表示职业、职位和官职.如：
He works in the school as a teacher of English.他在这个学校当英语教师.
Mr Wang is respected as a professor.作为一个教授,王先生受到人们的尊敬.
He was elected as chairman of the meeting.他被选为会议主席.
②扮演某角色.如：These ants act as guards and soldiers in time of trouble.
这些蚂蚁在出了乱子时,充当警卫和士兵.
The actor who appeared as Liu Ming was his friend.扮演刘明的那个演员是他的朋友.
③用在regard,look upon,treat等词后.如：
Today,Abraham Lincoln is regarded as one of the greatest of all American presidents.今天,亚伯拉罕·林肯被看作是美国最伟大的总统之一.
She took the leaflets regularly to the factory,looking upon this as her duty.她定期将传单带进工厂,把这项工作看成自己的责任.
They treat him as their own child.他们把他当作自己的孩子对待.
3.在下列情况下只能用for,不能用as.
①补足语表示“主观认识”时.如：
He was taken for a spy.他被当作奸细捉拿.
②补足语表示“交换”时.如：
The Negroes were sold for slaves.那些黑人被当作奴隶出卖了.
The old books can be changed for nothing.这些旧书什么也换不到.
③用在一些固定的词组中.如：
I know for certain.我确切知道.
He observed things carefully and never took anything for granted.
他仔细观察事物,从不想当然.
They were given up for lost.大家都认为他们已无生还的希望了
感谢你这个问题,给我也增加了点知识,这是我复制来的