定語從句中是需要引導詞的，那麼定語從句引導詞的省略又是怎麼樣的呢?
1、在非正式文體中，用於指人的關係代詞who whom, that 指代先行詞在定語從句中作賓語時通常可以省略;用於指物的關係代詞which和that指代先行詞在定語從句中作賓語時中也通常省略。例如：
1)The man (whom/who/that) we have just seen is a famous writer.
2)Where is the book (which/that) I bought last week?
2、 關係代詞指代先行詞在定語從句中作表語時，只用that ，它既可以指人，也可以指物，但時常省略。例如：
1)He is no longer the man that he used to be.
2)This is no longer the dirty place (that) it used to be.
3、以the way爲先行詞的限制性定語從句，如果先行詞way在定語從句中做狀語，通常以in which或 that 引導，但在非正式文體中，人們通常省略in which或 that 。例如;
1)The way (in which) he spoke to us was suspicious.
2)I don’t like the way (that) you laugh at her.
4、以place爲先行詞的.限制性定語從句，如果先行詞place在定語從句中做狀語，通常以where 引導，但在非正式文體中，人們通常省略where。例如：
1)This is the place (where) we met yesterday.
5、以reason爲先行詞的限制性定語從句，如果先行詞reason在定語從句中做狀語，通常以why引導，但在非正式文體中，人們通常省略why。例如：
1)That is the real reason(why) he did it.
6、以time,day,week,month,year等爲先行詞的限制性定語從句，如果先行詞在定語從句中做狀語，通常以when引導，但在在某些句型和某些時間狀語中，人們通常省略when。例如：
1)But help never stopped coming from the day she fell ill.
2)Each time he came, he did his best to help us.
注：針對以上情況，下列情形定語從句的引導詞不能省。
1、如果作介詞賓語且介詞提前，這時關係代詞指人用whom,指物用which，而且均不能省。例如：
1)Gun control is a subject about which Americans have argued for a long time.
2) She brought with her three friends,none of whom I had ever met before.
2)在非限制性定語從句中，無論是關係代詞還是關係副詞均不能省。例如：
1) They have won their last three matches, which I find a bit surprising actually
