一、非限制性定语从句不能用that引导。如:
1. I like the book, which was bought yesterday.我喜欢这本书,这是昨买的。
2. I like the book which/that was bought yesterday.我喜欢昨天买的那本书。
二、非限制性定语从句不能用why引导。要用for which代替why.如:
1. I had told them the reason, for which I didn’t attend the meeting.
我把理由告诉了他们,为此我不用去开会。
2. I had told them the reason why/for which I didn’t attend the meeting.
我告诉了他们我不去开会的理由。(限制性定语从句“the reason why…”是常见搭配。)
三、非限制性定语从句置于主句前时,不能用which引导;关系代词as引导非限制性定语从句位置比较灵活,可以放主句前,也可以放主句后。如:
1. As I expected, he didn’t believe me.正如我所预料的,他不相信我。
2. She heard a terrible noise, which brought her heart into her mouth.
她听到一个可怕的声音,这让她把心都提到嗓子眼了。
四、非限制性定语从句由“介词+关系代词”引导时,其中的关系代词不能用as,如:
1. He bought the car for more than $20000, with which his father was angry.
他花2万多美元买了这辆车,他父亲对此很生气。
2. I finished my work ahead of time, after which I sat some time reading the newspaper.
我提前完成了我的活,随后我坐着看了一会儿报纸。
五、非限制性定语从句中指人的关系代词作宾语时,只能用宾格whom, 不能用who替换,也不能省略。如:
1. Do you know Tom, whom we talked about? 你认识汤姆吗?我们谈到过他。
2. This book, which you can get at any bookshop, will give you all the information you need.
这本书会给你提供所有你需要的资料,它在任何一家书店都能买到。(非限制性定语从句中引导词在从句中作宾语,无论指人,指事物都不能省略)