定语从句与名词性从句的互换一、定语从句和名词性从句由于表达意思的需要，有时可以互相转换。
大致有下面三种情况：（１）定语从句与表语从句的互换That's the thing that we're worrying about.（定语从句）That's what we're worrying about.（表语从句）那就是我们正在担心的事。
This is the way she did it.（定语从句）This is how she did it.（表语从句）这就是她做这件事的方法。
This is the reason why we must go now.（定语从句）This is why we must go now.（表语从句）这就是我们现在该走的理由。
That is the place where Xiao Lin was born.（定语从句）That is where Xiao Lin was born.(表语从句)那就是小林出生的地方。
（２）定语从句与宾语从句的互换I don't know the reason why she is so happy.（定语从句）I don't know why she is so happy.（宾语从句）我不知道她为什么这样高兴。
He showed me the place where he used to live.（定语从句）He showed me where he used to live.（宾语从句）他带我看了他曾经住过的地方。
Do you know the date when Wuhan was liberated（定语从句）Do you know when Wuhan was liberated(宾语从句)你知道武汉是什么时候解放的吗（３）定语从句与主语从句的互换The thing that we need is more time.（定语从句）What we need is more time.（主语从句）我们所需要的是更多的时间。
The time when they will start out has not been decided yet.（定语从句）When they will start out has not been decided yet.（主语从句）他们什么时候动身还没有决定下来。
The reason why he did it wasn't quite clear.（定语从句）Why he did it wasn't quite clear.（主语从句）他为什么做那件事还不很清楚。
The place where she lives is not known yet.（定语从句）Where she lives is not known yet.（主语从句）她住在什么地方，大家还不知道。
二、学习定语从句应注意的几个问题（１）定语从句中关系代词与先行词的一致性定语从句中关系代词一般应与它所指代的先行词的单复数保持主谓一致。
例如：The students who were here just now are from No,2 Senior Middle School.但注意下列一组句子：He is the only one of the students who was here just now.He is one of the students who were here just now.如果"one of +复数名词"后跟有定语从句，一般情况下"one of"后的复数名词为先行词，但当one前有the only,the very,just the修饰时，先行词则为one。
（２）定语从句与强调结构It is the place where they lived before.It is in the place that they lived before.第一个句子为定语从句，where指代the place,在定语从句中作状语，第二个句子为强调结构，强调in the place,that没有意义，把in the place 放回后面句子，句子意思完整。
Where is it that he found the lost watch(强调句型，强调疑问副词where)。
Where is the watch that he found yesterday.(定语从句，that指代the watch)（３）定语从句与并列结构He has two sons,neither of whom looks like him.He has two sons,and neither of them looks like him.I've got two of them are in Shanghai.第一个句子为定语从句，关系代词whom指代two sons,在定语从句中作介词of的宾语。
第二个句子为并列结构，由并列连词and连接，人称代词them指代two sons。
第三个为两个独立的句子，两个句子中间用句号，两句开头的处一个字母都大写。
（４）定语从句与状语从句He found the books where he had put.He found the books in the place where he had put.第一个句子为状语从句，where he had put 作主句He found the books 的地点状语。
第二个句子为定语从句，where引导从句修饰the place。
This is such an interesting book that I'd like to read it.This is such an interesting book as I'd like to read.第一个句子为结果状语从句，在结果状语从句中，it指代book,作read的宾语。
第二个句子为定语从句，关系代词as指代先行词book的定语从句中read的宾语。
（５）定语从句中的先行词Is this book the one that you bought yesterdayIs this the book that you bought yesterday第一个句子中，this book是主句的主语，the one 是先行词。
在第二个句子中this 是主句的主语，the book是先行词。
一定要避免出现：Is this book that you bought yesterday（６）定语从句与同位语从句定语从句相当于形容词，它对先行词起修饰、描述或限制作用，而同位语从句则相当于名词，它对其前面的词给予说明或作进一步解释，即说明该词所表示的具体内容。
例如：The news that we heard is not true.(定语从句)The news that he won the prize is not true.(同位语从句)另：在"have no idea+从句"结构中，其从句都作idea的同位语。
例如：I have no idea when she will be back.三、把握定语从句中的时空概念在定语从句的运用中，当其先行词表示时间或空间概念时，有些学生很容易想当然地用关系副词when或where引导，而没有具体情况具体处理。
所以，应注意以下几点。
（１）从逻辑意义上讲，只有从句中的谓语动词与该先行词构成动状（时间、地点）关系时，才能用when或where引导从句；或视不同情况以prep.+which代之。
例如：1、This is the country where/in which Edison was born。
（动状关系）2、I'll never forget the year when/in which the terrible earthquake happened.(动状关系)3、England was one of the places from which the settlers moved to America.(动状关系)（２）从逻辑意义上看，当从句中的谓语动词与该类先行词有主谓关系或动宾关系时，则以which/that或prep.+which引导从句。
4、Please follow the custom of the country which/that you are going to visit.(动宾关系)5、For ever I'll remember the year that/which brought me happy memo ry.(主谓关系)6、He is going to work in Tibet which/that is far away from Hebei Province.(主谓关系)（３）从逻辑意义上讲，当从句中作主语的名词与先行词存在所属关系时，则用词whose。
7、is going to the country whose name is Sweden.(所属关系)8、Generally,we refer to the time whose speed is unchanged.(所属关系)浅述主动式定语从句的简化一、定语从句简化英语表达方式是相当灵活的，为了表达言简意赅，使叙述简洁明快，常用一定的语法手段把句子加以简化，定语从句被简化成简单句就是常见的一种。
下面简单谈谈主动式定语从句简化的几种情况。
（１）定语从句中的关系代词为从句主语，其谓语动词是现在进行时，可以用现在分词短语来简化。
例如：The man who is teaching us English now graduated from Hubei Univ ersity three years ago.-->The man teaching us...现在教我们英语的老师三年前毕业于湖北大学。
但是，如果定语从句动词之后没有介词作状语时，现在分词常置于中心词之前。
例如：The countries which are developing should get united.-->The developing countries should...发展中的国家应该团结起来。
（２）把定语从句简化为现在分词短语有以下几个条件。
1、从句的动词和主句的动作的时态的一致。