英语中助动词什么时侯该用?什么时侯不该用?任何分辨?如何用请赐教.

英语中助动词什么时侯该用?什么时侯不该用?任何分辨?如何用请赐教.

助动词在英语学习当中作了解,不需要重点把握,但是助动词也是很好理解的,希望回答能够帮到你.
1.助动词：Be
助动词不能作述语动词,要与本动词一起构成动词片语,表示时态、语态等.
1. BE作为本动词表示状态或客观存在等意思.
Your house is bigger and nicer than mine.
你的房子比我的又大又好.
2. BE+不定词连用,表示约定、义务、命令等未来的动作或状态.
I am to go abroad on business tomorrow.
明天我要去外国出公差.
表示未来的安排.
The meeting is to be held as scheduled.
会议将按原计划召开.
表示计划好的安排.
You are not to bark at my friend.
你不许对我的朋友叫.
表示命令或要求.
3. BE+现在分词构成各种进行时态.
Who are you talking to?
你在和谁说话?
I am talking to my dog.
我在和我的狗说话.
4. BE+过去分词构成被动语态.
That means I will be promoted as scheduled.
这就意味着我将要按原计划得到提升.
2. dare和used to
作为情态助动词的dare一般只能用于疑问句或否定句中,dare+原形动词表示敢.
I dare not say it is ugly.
我不敢说它丑.
How dare you say so?
你怎么敢这么说?
dare也可以作本动词,用于肯定句,后面要接带to的不定词;主词若是第三人称单数,简单现在式时,dare要变为dares.
You, you dare to talk to me like this!
你、你竟敢这样和我讲话!
used to+原形动词表示过去的习惯或状态,而现在已经不存在了.
You're not what you used to be.
你不是以前的你了.
used to构成疑问句时有两种形式.即used + 主词 + to + 其他成份?；Did + 主词 + use to+ 其他成份.
How used I to be?
我以前什么样?
How did you use to be?
你以前什么样?
used to构成否定句时有两种形式,即 used not to和didn't use to.
You didn't use to say things like this.
You used not to say things like this.
你以前不会说这样的话的.
be used to表示习惯于,其中used是形容词,to是介系词,后接名词、代名词或动名词等,可用于不同的时态.
You're used to hearing words of praise.
你是听好话听惯了.
3. 助动词：Do
1. DO作为助动词时的时态、人称和数的变化与它作为本动词相同,有do, does, did三种形式.
Yes, it seems he doesn't really want to have a haircut.
是啊,他好像不是真的想理发.
Then, why does he come here?
那他为什么来这里呢?
Where did he go when he left here?
他离开这儿去了哪了?
2. DO+主词+原形动词构成疑问句.
How long do I have to wait?
我得等多久?
3. DO+not+原形动词构成否定句.
No, I don't want to wait that long.
不行,我不能等那么久.
4. DO(+not)+主词用于附带问句.
You want to have a haircut, don't you?
你想理发,是吗?
5. DO+原形动词用于加强语气句.
Yes, I do want to have a haircut.
是,我真的想理发.
6. Never (Only)+DO+主词+原形动词用于倒装句.
Never did I see such a strange man.
我从未见过这么奇怪的人.
4. 助动词：Have
1. 助动词have+过去分词构成完成时态.
I have never seen such a strange man.
我从未见过这么奇怪的人.
Yes, he has been here twice but hasn't had his hair cut yet.
是啊,他来了两次还没把头发理了.
He's gone to your house.
他去你家了.
2. HAVE+受词+过去分词表示请或让别人做某事.
Can I have my hair cut now?
你现在可以给我理发吗?
Oh, you haven't had your hair cut yet.
噢,你还没理发呀.
3. HAVE+受词+原形不定词表示请或让某人做某事.
Or I can have my assistant help me do it.
或者我可以让我的助手帮我来做.
4. have作为本动词表示"有、拥有"的意思.
No, I don't have much time.
不行,我没那么多时间.
Oh, you still have many customers today.
噢,你今天还有很多顾客呀.
5. ought to和 had better
ought to+原形动词表示义务、劝告或推测等意义,意思是"应该…".
I am tired. I ought to sit here for a while.
我累了,我应该休息一会儿.
表示否定时,not放在ought之后.在美语中,在否定句中,ought之后的不定词符号to常可省略.
Hey, boy, you oughtn't (to) sleep here. Get up!
嘿,孩子,你不应该躺在这儿.起来!
在美语中,在疑问句中,ought之后的不定词符号to常可省略.
Ought you (to) do it?
你应该这么做吗?
had better只有一种形式,不是表示过去,而是指现在或未来,表示向对方提出劝告或警告.had better+原形不定词表示"最好...".
You had better give up smoking.
你最好把烟戒掉.
had better的否定形式是had better not.
You had better not throw it on the ground.
你最好别把它扔在地上.
had better很少用于疑问句,但有时为了表示忠告或建议而用否定疑问句,这时否定副词not位于主词之后.
Had you better not talk to yourself?
你不要自言自语好不好?
6. 助动词：shall和should
Shall用于第一人称,shall+原形不定词表示未来的动作或状态.
Really? Ok, I shall do what you said.
真的吗?好吧,我就按你说的办.
shall表示发言者或主词的意志,包括诺言、决心、强制等.
I shall never do such a thing.
我绝对不做这种事.
You shall give me a cigarette, or I shall tell the boss.
你必须给我一支烟,要不我就告诉老板.
shall用于询问对方的意向.
Where shall I meet you?
我在哪儿等你?
Should+原形动词表示过去未来.
So, I heard that you should get a promotion.
我听说你要被提升了.
should表示义务.
You should work harder.
你工作应该更努力.
惯用语 should like to 表示愿意,想要.
I should like to have another cigarette.
我想再来只烟.
should用于假设语气句.
You must put on more clothes lest you should catch a cold.
你必须多穿些衣服以免感冒.
7. 助动词：can和could
can, could在口语中相当于may, might,表示许可.
Can I help you, sir?
先生,我可以帮你吗?
could可表示客气的请求.
I am checking out. Could you give me the bill?
我要结帐.给我帐单好吗?
can, could表示能力,相当于be able to.
Of course we can wait.
我们当然可以等.
can,could表示怀疑、推测,一般用于疑问句或否定句.
Could it be the charge for the fruit?
这会是水果的费用吗?
can,could用于惯用语.can't help或couldn't help+动名词表示不得不、忍不住.
I can't help thinking you are ripping us off.
我不得不认为你们敲我们的竹杠.
8. 助动词：must和need
must表示必须、义务等,相当于have to, 但must强调主观因素,而have to强调客观因素.
I must go to see a doctor.
我得看医生去.
need可以对MUST引导的一般疑问句作否定回答.
Really? Must I go with you?
是吗?要我和你一起去吗?
No, you needn't.
不,没必要.
must的否定式表示不准,不得等禁止的意思,或表示不可,不能,一定不要等劝告的意思.
Ok, then, you mustn't forget your medical card.
好吧,那你一定不要忘记带医疗证.
我有必要说吗? 作为情态助动词的need一般只用于否定句或疑问句中,need+原形动词表示必要性.
Of course I remember. Need you remind me?
我当然记得了.你有必要提醒我吗?
must+have+过去分词表示对过去情况的推断.
Oh, it is wet outside. It must have rained yesterday.
噢,外面湿了.昨天想必是下雨了.
must+原形动词表示对现在情况的推断.
So it must be slippery outside. Do be careful!
所以外面一定滑.一定要当心.
need可用于假设语气,一般用于否定句中,后接不定词的完成式, needn't+have+过去分词表示过去不必做却已经做了的事.
I am not a little boy! You needn't have told me that much.
我不是小孩子.你不必和我讲那么多.
9. 助动词：Will
助动词will+原形动词构成未来式,表示未来的动作.
will用于第二人称的疑问句中,表示询问对方的意志或表示请求.
Will you give me a cigarette? Or I will tell the boss.
你给我一枝烟好吗?要不我就告诉老板.
will+原形动词表示推测.
This will be what you need.
这大概就是你所需要的.
will+原形动词表示一种现在的习惯动作或倾向.
She will stand there sleeping for hours.
她常常站在那儿一连睡上几个小时.
will+原形动词用于所有人称,表意愿.
Ok, I will do it.
好,我愿意做这件事.
情态动词精讲
,在英文中主要用来表示说话人的看法、态度等.它很接近中文里的能愿动词.从用法上来说,它有这样几个特点：
1）各个情态动词自身都有一定的词义.
2）情态动词不能在句中独立担当谓语.
3）情态动词在句中不受任何人称,性,数变化的影响.
4) 情态动词后接的不定式（除ought外）都不带to ,即接动词原形.
英文中的情态动词主要有：can , could ; may , might ; must ; ought ; need ; dare , dared ,另外,shall , will , should , would在一定的场合也可用作情态动词.例如：
He can speak five languages .他会说五种语言.
She must have arrived home by now .现在她准到家了.
We should study hard for our motherland . 我们应该为祖国而努力学习.
They needn't be in such a hurry for there is enough time
for them . 他们还有足够的时间,用不着这么慌张.
1. 常用情态动词的基本用法
can , could 能,会
（could可以看作是can的过去式,这两个词除了时态不相同外,在表达意思的许多方面是相同的.当然could也有自己独特的用法.）
1）表示脑力或体力上的能力
Nobody can stop the development of science .
谁也无法阻止科学的发展.
She can sing that song in English.她能用英文唱那歌.
He can submerge to a depth of about twenty meters .
他能潜入约二十米深的水中.
He could hardly support his family before he found the new job .他在找到那份新工作前几乎无 法养家.
I could not understand the lecture on the computer given by Mr. Smith .
我听不懂史密斯先生作的那个关于计算机的讲座.
2)表示客观上的可能性
You can borrow this useful book from the library .
你可以从图书馆借到这种有用的书.
A more suitable person than him for the job can not be found . 不可能找到比他更适合这份工作的人了.
Now people can skate on the lake .现在人们可以在湖上滑冰了.
When the storm stopped , the plane could take off .
当风暴停下来时,飞机可以起飞了不得.
3)表示主观上的允许
Can I ask you some questions about it ?
我可以问你有关这件事的几个问题吗?
You can not leave here till I come back .直到我回来你才能离开.
Such kind of thing can't happen any more later .
这类事以后不准再发生了.
Can you tell me how to get to the airport ? 你能告诉我怎么去机场吗?
Could you tell me how to get to the airport ?
您能告诉我怎么去机场吗?
Could I be forgiven my negligence ? 请原谅我的疏忽,行吗?
4）（用于否定句、疑问句或感叹句中）表示猜测、怀疑或惊诧
How can / could you be here ? 你怎么会在这儿?
She couldn't / can't be so stupid to do that .
她不可能蠢得去做那种事吧.
He couldn't / can't be over seventy .他不可能有七十多岁了.
Where could / can the boy be now ? 那孩子现在能在哪儿呢?