名词性从句中的引导词—that、if与whether 一、 that引导的名词性从句 that引导名词性从句时，可引导主语从句、表语从句、宾语从句和同位语从句，that 在从句中既不充当任何成分，也无实际意义，仅起着连接句子的作用。例如： 1) That a new teacher will take charge of our class is true. (that引导主语从句) 2) Can you believe (that) in such a rich country there should be so many poor people? ( that引导宾语从句，that可省略) 3) We heard the news that our team had won. (that引导同位语从句) 4) Another problem is that good soil is gradually lost. (that引导表语从句) 注意：that在以下情况下不能省略 ①that引导的宾语从句作介词宾语时，that不可省略。例如：I know nothing about him except that he is from the south. ②that引导的从句位于句首时，that不可省略。例如：That he finished writing the composition in such a short time surprised us all. ③及物动词后由that引导的两个或两个以上的并列宾语从句中，只有第一个that可省略。例如：Mother said (that）you needn’t worry and that she would help you. ④主句谓语动词与that从句之间有插入语时，that不可省略。例如：Mother judged that, because Jim was still a child, he didn’t understand her words. 二、 if和whether引导的名词性从句 if和whether引导的宾语从句表示“是否”之意时，可以互换。例如：I wonder whether/if daughters are valued as much as sons in the countryside. 但在以下几种情况下，只能用whether(不用if)引导名词性从句： 1) 在句首引导主语从句时，或引导表语从句、同位语从句时，只能用whether。例如：①Whether she will go abroad or not is unknown. (whether引导主语从句) ②The question is whether we can collect enough money for the project. (whether引导表语从句) ③I have no idea whether Liu Xiang will win the championship in the 2008 Olympic Games. ( whether引导同位语从句) 2) 引导介词宾语从句时只能用whether。例如： It all depends on whether he is coming back on time or not. ( whether引导的从句作介词on的宾语) 3) 与or not连用或后接动词不定式时，只能用whether。例如： ①I wonder whether you will help me or not. (whether与or not连用) ②Can you tell me whether to go or stay? (whether后接动词不定式) 本文来源：https://www.wddqw.com/doc/6de224ac0b1c59eef9c7b49a.html