一、三者在意义上的区别三者都可表示“除外”,但 besides 表示一种累加关系,意指“除了什么之外,还有……”;而 except 或 but 则表示一种排除关系,意指“除了什么之外,不再有……”。如:Besides his wife,his daughter also went to see him. 除他妻子外,他女儿也去看过他(即妻子女儿都去看过他)。Nobody went to see him except [but] his wife. 除他妻子外,没有一个人看过他(即只有他妻子去看过他)。注:在否定句中,besides 也表示“除……之外不再有…… ”,与but, except 同义。如:No one passed the exam besides [except] Jim. 除吉姆外,没一个人通过考试。二、but 与 except的主要区别(1) 两者都可表示“除……外不再有……”,但含义上略有差别:but侧重指意义的几乎完整性,而 except 则侧重指后面除去的部分。比较:All are here but one. 除一个人都到了。All are here except one. 还有一个人没到。(2) 在现代英语中,but 的介词用法十分有限,一般说来,它只能用在下列词语之后:① no, no one, nobody, nothing, nowhere 等② any, anyone, anybody, anything, anywhere 等③ every, everyone, everybody, everything, everywhere 等④ all, none 等⑤ who, what, where 等Everyone knows it but you. 除你之外大家都知道。I haven’t told anybody but you. 除你之外,我没告诉任何人。No one but he [him] showed much interest in it. 除他之外没有一个人对此有很大兴趣。一般说来,若没有出现上述词汇,就不宜使用介词 but,否则可能造成错句。但是 except 却没有以上限制。比较:正:The window is never opened except in summer. 除夏天外,这扇窗户从不打开。误:The window is never opened but in summer.(3) but 一定不能用于句首,except 通常不用于句首:除我之外每个人都累了。正:Everyone is tired but (except) me.正:Everyone but (except) me is tired.误:But (Except) me, everyone is tired.注:except for 可用于句首,表示 except 的意思:正:Except for me, everyone is tired.三、except 与 except for的用法区别except 主要用来谈论同类的东西,而 except for 则主要用来谈论不同类的东西,有时含有惋惜之意。如:All compositions are well written except yours. 除了你的作文外,其他的作文都写得很好。His composition is good except for a few spelling mistakes. 他的作文写得不错,只是有几处拼写错误。注:若用于句首,则 except for 与 except 同义(但 except 通常不用于句首)。四、except for 与 but for的用法区别except for 主要表示排除,but for 主要表示一种虚拟条件(与虚拟语气连用)。如:Except for me, everyone passed the exam. 除了我之外,大家都通过了考试。But for my help, she would not have passed the exam. 若不是我的帮助,她就不会通过考试。But for the atmosphere plants would die. 如果没有大气,植物就会死亡。五、一点补充说明besides 除用作介词外,还用作副词,其意为“此外”、“而且”,可用于分句句首(通常用逗号隔开)或句尾。如:I don’t want to go; besides, I’m too tired. 我不想去,而且我也太累了。This car belongs to Smith, and he has two others besides. 这部车是史密斯的,此外他还有两部。