whether和if引导的从句

whether与if一、相同之处。 1. whether和if常置于see, ask, say, learn, tell, wonder, doubt, find out, be uncertain/doubtful/be not known等动词之后引导宾语从句，通常可以互相替换，口语中多用if代替whether。在非正式的写作中，可以使用if 或 whether 两个词来表达不定性，两者都算标准。例如 ： We shall soon learn whether/if it is true. He asked me whether/if I could help him. I want to know whether/if he lives there. Ask if/whether he plans to come to the meeting.我的桌面上“我的电脑”和“我的文档”都成.2. whether和if都可用it作形式主语从句中。如： its uncertain whether/if hell come this evening. 3. 在be uncertain/doubtful/be not known之后，常用whether引导宾语从句，有时也可以用if，如： We are uncertain whether/if Mary will come. 二、不同之处。 1. whether可置于句首引导主语从句，if则不能。如： Whether the 2000 Olympic Games will be in Beijing is not known.Whether the football game will be played depends on the weather.Whether he will come is still a question.若在句首使用形式主语 it，而将主语从句放在句末，则有时也可用 if 来引导。如： It was not known whether/if he would come. 2. whether可引导表语从句，if则不能。如： The question is whether it is not worth doing. The question is whether he can do it.The question is whether we should go on with the work.3. whether可引导同位语从句时，if则不能。如： The question whether the students answered correctly should be decided by the teacher. The question whether we should go with them must be decided at once.4. 宾语从句置于句首表示强调时，用whether，不用if。如：Whether this is true, I cant say.Whether he is single, I dont know.5. 在介词之后只能用whether引导宾语从句，而If则不能。如： Success depends on whether we make enough effort. I havent settled the question of whether Ill go back home.It depends on whether the letter arrives in time. I worry about whether I hurt her feelings. 6. 在动词不定式之前只能用whether，而if不能。如： Please tell us whether to go or stay here. Whether to go or stay is still a question.Im not sure whether to stay or leave. I didnt know whether to laugh or to cry. 7. 在某些动词（如discuss，decide）之后，只能用whether，而不用if引导宾语从句。如：We discussed whether we should close the shop. （虚拟语气）We discussed whether we should go there by plane.（虚拟语气）We discussed whether we should hold a meeting. （虚拟语气）8. 在引导否定概念宾语从句时，只能用if，而不用whether。如：He asked me if I hadnt finished my work. 注：doubt否定句用that引导。因为dont doubt 意为相信，不怀疑，if是否表示疑虑。 9. 与 or 连用分别引导两个从句时，或强调两方面的选择, 特别是句中有or not时用whether，不用if。如： I dont know whether he is wrong or she is wrong.Let me know whether you can come or not.I dont know whether he will win or not.I will write to you whether or not I can come/ whether I can come or not.or 若不是引导两个从句，而是连接两个词或短语，则也可用 if (但不如用 whether 常见)。如： He didnt know if/whether we should write or phone.10. 用if会引起歧义或者句中已经有一个引导条件状语从句的if时，用whether。11. if还可以引导条件状语从句，是“假如、如果”之意，而whether还可以引导让步状语从句（在句中不充当成分），是“不管、无论”之意。如：If you ask him, he will help y