whether和if的用法區(qū)別
whether與if作“是否”講,在用法上有相同之處,也有不同之處.
一、相同之處.
1.whether和if都能引導(dǎo)賓語(yǔ)從句,常置于see,ask,learn,tell,wonder,doubt,find out等動(dòng)詞之后.
如：He asked me whether/is I could help him.I want to know whether/if he lives there.
2.whether和if都可用it作形式主語(yǔ)從句中.如：it's uncertain whether/if he'll come this evening.
3.在be uncertain/doubtful之后,常用whether引導(dǎo)賓語(yǔ)從句,有時(shí)也可以用if,如：We are uncertain whether/if Mary will come.
二、不同之處.
1.whether可置于句首引導(dǎo)主語(yǔ)從句,而if不能.如：___the 2000 Olympic Games will be in Beijing is not known yet.A.whether B.If C.Whether D.That 答案是C.
2.whether可用在介詞之后,引導(dǎo)賓語(yǔ)從句,而If則不能.如：Success depends on whether we make evough effort.
3.whether可引導(dǎo)表語(yǔ)從句,if則不能.如：The puestion is whether it is not worthdoing.
4.在名詞之后引導(dǎo)同位語(yǔ)從句時(shí),用whether而不用if.如：The puestion whether the students answered correctly should be decided by the teacher.
5.whether后可接不定式,而if不能.如：Please tell us whether to go or stay here.
6.在有些動(dòng)詞（如discuss）之后,只能用whether,而不用if引導(dǎo)賓語(yǔ)從句.如：We discussed whether we should close the shop.
7.在引導(dǎo)否定概念in賓語(yǔ)從句時(shí),只能用if,而不用whether.如：he asked me if I hadn't finished my work.