【导语】be+不定式”是一个很有用的结构，它不仅在中学教材中经常出现，而且在高考题中也经常出现。结合中学生学习和考试的实际情况，将该结构的用法归纳如下。快来看看吧！希望能帮助到你~更多相关讯息请关注！
一、表示将来或预计
I don’t know what is to happen to us. 我不知道我们会发生什么事。
I went to have a look at the room where I was to talk that afternoon. 我去看了一下地方，当天下午我要在那里讲话。
It was 1491. Columbus was to reach America a year later. 那是1491年，一年后哥伦布到达了美洲。
说明：当该结构中用了still 或 yet 时，其将来意义更加突出。如：
The worst is still to come. 还有最糟糕的事情要发生。
The most severe weather is yet [still] to come. 最恶劣的天气还没有到。
The best item on the programme is still to come. 看的节目还在后头。
注意，该结构表示将来的用法是有限的，原则上，只有当表示的动作为人所控制时才可使用它来表示将来，否则就是错的。如可说 I’m going to play tennis，也可说 I’m to play tennis，因为其中的 play tennis是可以人为控制的。而在以下各例中，其中的动作均不能为人所限制，所以going不可省略：
He’s going to be fat. 他要发胖了。
There is going to be a storm. 要下暴风雨了。
You’re going to break that chair. 你会把那把椅子弄坏的。
二、表示计划或意图
They are to be married. 他们打算结婚。
We are to be married in June. 我们计划在6月结婚。
说明：该结构也可用于条件状语从句。如：
If I’m to be there on time, I must leave at once. 如果我要想准时赶到那儿，我就必须马上动身。
If we are to succeed in this enterprise, we shall need to plan everything very carefully. 如果我们想要在这项事业上取得成功，我们就需要把一切都仔细计划好。
另外，若表示过去未曾实现的想法或意图，其中的不定式则用完成式。如：
We were to have gone away last week, but I was ill. 我们本打算上周走的，但是我病了。
I was to have started work last week, but I changed my mind. 我本该上周开始工作的，但我改变了主意。
比较：
He was to go. 当时他是要去的。(至于最后去没去，不得而知)
He was to have gone. 他本来是要去的。(但实际上却没有去)
三、表示责任或义务
You are to report to the police. 你应该报警。
I am to inform you that... 我有义务(我受人之托)通知你……
She is to be in class at 9 am. 她应该上午9点到课堂。
四、表示命令或规定
You are not to smoke here. 此处禁止吸烟。
All staff is to wear uniforms. 全体工作人员必须穿制服。
Visitors are to leave when the bell rings. 来访者必须在铃响时离开。
You are to do your homework before you watch TV. 你得做完了作业才能看电视。
She can go to the party, but she’s not to be back late. 她可以去参加聚会，但不能晚回来。
No one is to leave this building without the permission of the police. 未经警务人员允许，任何人不得擅自离开这座房子。
五、表示目的或用途
A knife is to cut with. 刀子是用来切东西的。
The telegram was to say that she"d be late. 电报是说她可能晚到。
六、表示推测或推断
He is not to be blamed. 不该责备他。
The book was not to be found. 那本书找不到了。
The account of the event is to be found in today’s papers. 关于这件事的报道可在今天的报上找到。
七、表示命中注定
He was never to see his wife again. 他从那以后就再也见不到他的妻子了。
They were never to meet again. 他们注定以后永远不会再见面。
They said goodbye, little knowing that they were never to meet again. 他们相互道别，一点也没有想到他们再也不能相见了。
八、表示虚拟语气
即用于与事实相反的虚拟条件句，表示虚拟语气。此时be通常要用were这一形式，但在非正式文体中也可用was。如：
I’d be sorry if you were to think that I disliked you. 若是你认为我不喜欢你，那我就太伤心了。
If it were to rain, we would have to cancel the match tomorrow. 假如下雨, 我们只好取消明天的比赛。
注意其省略倒装形式：
If I were to tell you / Were I to tell you that I killed him, would you believe me? 假如我对你说是我杀死了他, 你相信吗?
If I were to do that / Were I to do that, what would you say? 如果我做了那件事，你会说什么呢?
说明：根据语意的需要，“be+不定式”结构中不定式可以用被动式。如：
The cover is not to be removed. 这块盖布请勿揭开。
This medicine is to be taken hourly. 这药每小时服一次。
The cost of carriage is to be paid by the receiver. 运费由收货人支付。
She will determine how it is to be done. 她会决定这件事的做法。
A little tiredness after taking these drugs is to be expected. 服下这些药后会有些疲倦。
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