一、定义
宾语从句是名词性从句的一种。在主从复合句中充当宾语，位于及物动词、介词或复合谓语之后的从句称为宾语从句。
因此，有人把宾语从句分为动词后的宾语从句、介词后的宾语从句和形容词后的宾语从句。如：
动词后：I don't know when he came back.
介词后：I'm thinking about who is the right person for the position.
形容词后：He's sure she will win the game.
二、引导词
能够引导宾语从句的词语主要有：
that/if/whether
who/whom/whose/which及其-ever结构how/why/when/where及其-ever结构
what
（一）that引导的宾语从句
that引导宾语从句时，就是起着连接作用，不在从句中作成分。如：
I think that it's very interesting to experience a different culture.He didn't know that he had been to the lecture last night.
此时的that经常被省略，所以上面两句可以改为：
I think it's very interesting to experience a different culture.He didn't know he had been to the lecture last night.
需要注意的是，也有that不可省略的情况，常见的有：
1、that作learn、suggest、explain、agree、wonder、prove、mean、state、feel、hold等动词的宾语时。如：
She explains that Jack did do the job by himself yesterday.
2、一个动词带有两个或两个以上宾语从句时，第一个that可以省略，第二个that不可以省略。如：
She thinks (that) we did a good job and that things will get better soon.
3、宾语从句中的主语是指示代词this/that/those/these做主语的定语时。如：
We're glad that this book helps you a lot in your research.
4、宾语从句是双宾（直接引语和间接引语）中的直接宾语时。如：
He told me that he really liked my lessons.
5、当宾语从句前置时。如：
That he is sure to help, I believe.
6、当it作形式宾语时。如：
She made it clear that he was the one who was in charge of the company.
（二）if/whether引导的宾语从句
当宾语从句要表达“是否”的含义时，连接词语就用if/whether，其主句的谓语动词往往是know、ask、care、wonder、find out等词。如：
He didn't know if/whether she would attend the meeting tomorrow.
注意以下情况一般都用whether，不用if：
1、介词后的宾语从句一般不用if。如：
She's very curious about whether he is a teacher.
2、在具有选择意义，又有or或or not时，尤其是直接与or not连用时，往往用whether（if…or not也可以使用）。如：
I don't know whether/if he comes from England or not.
3、宾语从句置于句首时，不能用if。如：
Whether the book is hers or not, he's not sure.
4、当用if会引起歧义时，则须使用whether。如：
Please tell me if you like the job.
上面的句子有两种可能的含义，即：
1）If you like the job, please tell me.2) Please tell me if you like the job or not.
所以，如果是要表达第2）的含义，为了避免歧义，就要采用whether，即：
Please tell me whether you like the job.
（三）特殊疑问词引导的宾语从句
这种情况下的连接词有两大类：一类是代词，如who/whom/whose及其-ever结构，还有一类是副词，如how/why/when/where及其-ever结构。如：
He wanted to know who had broken the window.
The school will punish whoever breaks the rules.
The teacher told us why it was wrong to tell lies.They told me when the accident had happened.
（四）what引导的宾语从句
what引导宾语从句时，既起着连接作用，又在从句中充当主语和宾语等成分。如：
主语：We really wonder what matters most to him.宾语：I hope to find out what he's interested in.