whether和if的用法区别 1)whether和if常用来引导宾语从句,这时两者的含义区别很小,一般可通用.例如：①I don't know whether/if they will come to help us.我不知道他们是否来帮助我们.②I am not sure whether/if I'll have time to go with you.我很难说我们是否有时间跟你们一起去.上面两句无区别.但是,当whether与or not连成一个词组时,whether不可换用if.例如：③I don't know whether or not they will come for our help.我不知道他们是否要来求我们支援.【注意】若whether和or not不连在一起,在日语中可以用if取代whether,当然也可以用whether.例如：④I am not certain if/whether the train will arrive on time.我没有把握火车是否准时到达.⑤I don't care if/whether your car breaks down or not.我不在乎您的车是否是会出故障.此外,还有三种情况值得注意：(1)在介词后面只能用whether,不能用if.例如：①This depends upon whether we are determined to do it.这件事要看我们是否有决心去做.②It depends on whether he is ready.这件事要看他是否有准备.③I am not interested in whether you'll come or not.你来不来我不感兴趣.④We haven't settled the question of whether we'll renew our supplies of coal for factory.是否要为我们工厂补充一些煤,这个问题我们还没有决定.(2)在动词不定式之前,只能用whether,不能用if.例如：①He doesn't know whether to stay or not.他不能知道是否要留下来.②She doesn't knows whether to get married now or wait.是否现在结婚或是等待她不知道.(3)在及物运动discuss后的宾语从句中,只能用whether,不能用if.例如：①We discussed whether we should make a change in our plan.我们讨论了是不是要对我们的计划作一些修改.②We were discussing whether we should discuss the business with them.我们正在讨论我们是否要和他们谈这个生意.2)引导主语从句时,只能用whether,不能用if.例如：①It is unknown whether he will come.他是否来还不知道.②Whether the news is true remains a question.这个消息是否真实仍然是个问题.3)引导表语从句时,只能用whether,不能用if.例如：①What we want to know is whether he will come to speak to us tomorrow.我们想知道的是他明天是否来给我们讲话.②The question is whether they can take our advice.问题是他们是否能接受我们的意见.4)引导同位语从句时,常用whether.例如：①The question whether we'll build another lecture building hasn't been settled.是否要另建一幢教学楼的问题还未决定.②The question whether he'll come is unknown.他是否来的问题还不知道.5)可以用来引导一个否定的宾语从句,whether则不能用来引导否定的宾语从句,因为它表示正反两方面的选择意义比较强.例如：①Tell me if it is not going to rain,please.请告诉我明天是否不会下雨.②He considered if he shouldn't tell her the secret.他考虑他是否不该告诉她这个秘密.6)if除引导宾语从句外,还可以引导条件状语从句,作“是否”解.在容易引起混淆产生歧义的情况下,就不可用if,而须用whether.例如：①Please let me know if you intend to come.这个句子有两种解释：A：“请让我们知道你是否想来.” B：“如果你打算来,请让我们知道.” 第一种解释是把if引导的从句看作宾语从句,把动词know视为及物动词(vt．)；第二种解释是把if引导的从句当作条件状语从句,把动词know看作不及物动词(vi．).在口语中,我们可以通过语调来表示两者的区别；但是,在书面语中,无上下文(如一张便条上写着这句话),那就含混不清了.如果我们想表达的第一种含义,就得用whether来改写第一句.①Please let me know whether you intend to come.又如：②Let me know whether he has left for Shanghai.告诉我他是否已经去上海了.③Let me know if he has left for Shanghai.如果他去上海,请告诉我一声.