首先for fear that主语+(should) should +动词原形
意为“以免，唯恐，生怕，唯恐”。常用于引导目的状语从句表示否定（注意是常用于，因为还可以引导原因状语出），一般只用于书面语。首先，这个引导目的状语从句的that是可以说 省略的。
1、连接词“for fear that”可以用来引导虚拟语气。
其形式通常为：“for fear that +主语+ should +动词原形”。
She examined the door again for fear that a thief should come in.
她又把门检查了一遍，以防盗贼的进入。
He started out earlier lest he should be late.
他很早就出发了以防迟到。
2、句中的should可以省去：
They burned all the important documents for fear that they fall into the enemy's hands.
他们将所有的重要文件都烧毁了，以免它们落于敌人之手。
I will not make a noise for fear that I (should) disturb you.
我不会做声的，以免打扰你。
He walked fast for fear that he（ should） be late.
他快走,以免迟到；
3. 引导原因状语从句，相当于because,“是因为怕”“因为担心”“ (引出产生某种情感的原因)唯恐，担心”
这个时候从句中的形态动词可以是should 、may、would、might等
Shut the window for fear (that) it may rain.关上窗户，恐怕要下雨。
They wouldn’t let their cats run around outside for fear that it would get run over by a car.= They wouldn’t let their cats run around outside because they were worried that it would get run over by a car.
他们不肯让猫在外面乱跑，是因为怕猫被车压了。（生怕猫被汽车压了。）
He went out in disguise,for fear that someone might recognize him.
他化妆外出，因为他怕有人认出他。（以免有人认出他。）
The government, however, did not accept the suggested plan for fear that shutting off power supply for even one minute would lead the whole nation into great confusion.(摘自全国成人高考试题)
然而，政府不接受建议的计划，因为担心切断电源一分钟甚至会导致整个国家陷入巨大混乱。
另外：
for fear that……should/would/might/may……
for fear that引导的从句里，可用should/would/might/may等词，如：
He’s working hard for fear that he should would/might/may fall behind.
他在努力工作，担心自己会/可能/落后。
I daren’t tell you what he did,for fear that he should be angry with me.
我不敢告诉你他干了什么，以免他生我的气。
He handled the instrument with care for fear (that )it should be damaged.
他小心翼翼地使用那台仪器，生怕把它弄坏了。
She worried for fear that the child would be hurt.
她因怕孩子受伤而担忧。
Shut the window for fear (that) it may rain.关上窗户，恐怕要下雨。
He worked hard for fear that he might be fired by the boss.
他拼命地干活惟恐被老板解雇。
They didn’t say much for fear that the others might hear them.
She was afraid lest she had revealed too much.
她担心她泄露得太多了。（原因状语从句）
知识扩展
1.for fear that的近义词：lest
lest
读音：英 [lest] 美 [lest]
释义：免得，以免，(引出产生某种情感的原因)唯恐。
语法：lest所引导的从句中谓语动词要用虚拟式，即“(should+)动词原形”。
例句：
I was afraid to open the door lest he should follow me.
我不敢开门，唯恐他还跟着我。
He gripped his brother's arm lest he be trampled by the mob.
他紧抓着他兄弟的胳膊，怕他让暴民踩着。
I was afraid to open the door lest he should follow me
我不敢开门，唯恐他还跟着我。（原因状语从句）
《柯林斯高阶英汉双解学习词典》
They spoke in whispers lest they should be heard.
他们低声耳语惟恐被人听见。（原因状语从句）
《汉英大词典》
The president has gone along with the hardliners lest they be tempted to oust him
总统同意了强硬派的意见，以免他们产生赶他下台的念头。（目的状语从句）
《柯林斯高阶英汉双解学习词典》
Close the window quickly lest the raindrops ( should) slant in.
快关窗户，别让雨点潲进来。（目的状语从句）
《汉英大词典》
Read in a good light lest it should hurt your eyes.
到明处来看书，免得搞坏了视力。（目的状语从句）
《汉英大词典》
2. 凡是由lest（以免；免得），in case（以防）和 for fear that（生怕，唯恐）引导的目的状语从句中，用“should+动词原形 其谓语部分should可以省略。例如：
Keep quiet in case you（should）interrupt him
when he is busy．要保持安静， 以防打扰他。
She is now studying for fear that she（should）fail in
English．她现在很勤 奋，生怕英语不及格。
You must wake him early lest he（should）be late for
school．你务必早点叫 醒他，以免他上学迟到。
但是，in case引导的从句也可以是陈述语气，即根据事实等情况该用什么时态就用什么时态：
Dad brought a notebook along to the beach, in case he was seized by sudden inspiration.
爸爸带了一个笔记本去海滩，如果突然有了灵感可以记录下来。
《柯林斯高阶英汉双解学习词典》
In case I forget, please remind me of my promise.
假如我忘记了，请提醒一下我的诺言。
《汉英大词典》
We wanted to be here early in case the whatsit, maintenance supervisor had forgotten todeal with it
我们想早点儿到这儿，以防那个什么维修主管忘了处理这件事。
《柯林斯高阶英汉双解学习词典》
In case anyone was following me, I made an elaborate detour
为了防止有人跟踪我，我特地绕了弯路。
《柯林斯高阶英汉双解学习词典》
Don't forget to take your umbrella in case it rains.
别忘了带伞，下雨好用。
《汉英大词典》
In case you give me leave, I will start at once.
如果你许可，我立即就动身。
《汉英大词典》
In case you think I was incautious, take a look at the map.
如果你认为我不够仔细，就自己看看地图。
《柯林斯高阶英汉双解学习词典》
In case there is any divergence of interpretation of this agreement, the* text shall prevail.
如对本协定在解释上遇有分歧应以*文为准。
《汉英大词典》
Never walk behind a horse in case it kicks out ( at you).
千万不要走在马后，它会踢你的。
《汉英大词典》
I like to keep a few envelopes about in case I need them.
我喜欢在手头留存一些信封，以备不时之需。
《汉英大词典》
You must remind him to take his medicine, in case he forgets.
你要钉着他吃药，别让他忘了。
《汉英大词典》
Please keep an eye on the stove in case the milk boils.
劳神照料炉上的牛奶，别沸溅了。
《汉英大词典》
I was going to get out of the building in case it went up
我怕大楼起火，正打算要跑出去。
《柯林斯高阶英汉双解学习词典》
She is afraid to contact the social services in case they are labelled a problem family.
她不敢联系社会服务部门，以免被当作问题家庭。
《柯林斯高阶英汉双解学习词典》
Leave your key with a neighbour in case you lock yourself out one day.
给邻居留把钥匙，以防有朝一日把自己反锁在外面。
《柯林斯高阶英汉双解学习词典》
The authorities have urged people to stock up on fuel in case hostilities break out.
当局已敦促人们储存燃料，以防战事爆发。
《柯林斯高阶英汉双解学习词典》
I had to keep the video camera readily accessible in case I saw something that needed to befilmed.
我必须将摄像机放在触手可及的地方，以便需要拍摄时用得上。
《柯林斯高阶英汉双解学习词典》
The blackbird had a quick, wary look in case the cat was anywhere around
这只乌鸫迅速警惕地张望了一眼，以防那只猫就在附近。
《柯林斯高阶英汉双解学习词典》
He left the door ajar in case I needed him.
他虚掩房门，以防我会需要他。
《柯林斯高阶英汉双解学习词典》
You'd better take the keys in case I'm out.
你最好带上钥匙以防我不在家。《牛津词典》
In case (= if it is true that) you're wondering why Jo's here─let me explain.
我来解释一下吧，免得你奇怪乔为什么在这儿。《牛津词典》
She's nervous about something, in case you didn't notice
她正为了什么事神经紧张，你连这个都没看出来？
《柯林斯高阶英汉双解学习词典》
Extra boiling water should be kept at hand just in case it is needed.
身边应多准备一些开水，以备不时之需。
《柯林斯高阶英汉双解学习词典》
'I'm waiting for Mary Ann,' she said, 'in case you're wondering.'
“我在等玛丽·安，”她说，“要是你想知道的话。”
《柯林斯高阶英汉双解学习词典》
3. for fear of +doing/名词性词组或词。表示“怕，以免，害怕，担心”
No one dared shoot for fear of hitting Pete.
没人敢开枪，怕伤着皮特。
《柯林斯高阶英汉双解学习词典》
I have omitted calling on you for fear of disturbing you.
我怕打扰你而没有来拜访你。
《汉英大词典》
She was afraid to say anything to them for fear of hurting their feelings
她什么都不敢对他们说，以免伤害他们的感情。
《柯林斯高阶英汉双解学习词典》
People don't like to ask questions for fear of appearing ignorant
人们不喜欢问问题，害怕自己会显得很无知。
《柯林斯高阶英汉双解学习词典》
People are afraid to venture out for fear of sniper attacks
由于害怕狙击手，人们不敢冒险外出。
《柯林斯高阶英汉双解学习词典》
He didn't want any further involvement for fear of retribution.
他担心受到惩罚，不想再牵涉其中。
《柯林斯高阶英汉双解学习词典》
The report was held back for fear of prejudicing his trial
因为担心会使他的审判有失公正，这篇报道被暂时压了下来。
《柯林斯高阶英汉双解学习词典》
We spoke quietly for fear of waking the guards.
我们悄悄说话，以免惊醒警卫。《牛津词典》
4.虚拟语气主要用来表示假设，而非客观存在的事实，所陈述的是一个条件，不一定是事实，甚至完全与事实相反。虚拟语气通过谓语动词的特殊形式来表示。
英语中的语气分为陈述语气、祈使语气、虚拟语气、疑问语气和感叹语气五类。虚拟语气表示说话者做出的假设而非事实，或难以实现的情况，甚至表达彻底相反的概念。此外如需表达主观愿望或某种强烈的感情时，也可用虚拟语气。
最后，有这样两个经典例子，感觉非常有意思，现在分享给大家，希望大家在评论区展开讨论：
He worked hard for fear that he might be fired by the boss.
他拼命地干活惟恐被老板解雇。
《汉英大词典》
I had to run away for fear (that) he might one day kill me.
我只好逃走，生怕他有一天把我杀了。
《牛津词典》
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