情态动词shall ,will ,should和would 在不同的句子中含有不同的意思，其基本用法如下：一、shall1. 表示说话者的意图、允许、警告、命令、决心等，用于陈述句的第二、第三人称中，有必须，应，可之意。

例如：１）You shall have that book tomorrow.2) He shall be punished if he insists on doing that.2,. 在问句中表示征求对方意见，主要用于第一、第三人称，有“…..好吗”，“要不要”等意思。

例如“1) Shall I fetch the hammer?2) Shall those goods be sent over to you at once?3) Shall we help you?2. 用在表示意图、要求等的从句中，有“应该”，“要”之意，例如：My demand is that is shall be done in time.二、should1.表示义务、责任、建议或劝告，有“应当、应该”的意思。

例如：1) You should learn from each other.2) You shouldn’t be so careless.3) He should have told me the news earlier.(should + have + 过去分词)表示对过去本该做的事而没有做，其否定形式是对过去本不做的事而做了的固定句型。

２．与why ,who ,how等词连用，表示意外、惊异等，有“竟会”等意思。

例如：1) How should I know?2) Why should you be so late today?３．用于表示建议、命令、决定等的从句中，有“应该、必须”的意思。

例如：1) The young doctor proposed that he should try the experiment on himself.2) It was decided that we should start a cleanup at once.４。

表示可能性、推测或推论，有“可能、该”等意思。

例如：They should have arrived in Beijing by this time.５．用于虚拟语气句子中，有“万一、竟然、就、该”等意思。

例如：1) Should it rain tomorrow (或If it should rain tomorrow ) ,the meeting would be postponed.2) If the book were in the library ,you should have it. (should 在句子里表说话人的意愿)三、will１．表示意志、意愿，有“愿、要”之意。

例如：1) We will fight on until final victory is won.2) I will do my best to help you.3) She will not shove the heavy load on to others.２．在疑问句中用于第二人称，表示说话人向对方提出请求或询问对方的意思，有“你…..好吗、你愿…..”。

例如：1) Will you help me with my work?2) Will you join our discussion?３．表示习惯、经常性、倾向性，有“惯于、总是”等意义。

例如：Every morning he will have a walk along this river.４．在if ,when ,until等连词引导的表示时间或条件的从句中要用一般时表将来，但在if 从句中有时为了表示意愿也可用will ，有“愿意”的意思。

例如：1) If you will read this article ,you will realize you are wrong.2) If they won’t help us ,we can not finish the task within one month.四、would１．Will 的过去式，表示对过去时间的意志、意愿、决心，有“愿、要、偏要”的意思。

例如：1) I promised that I would do my best.2) I told him not to go ,but he would not listen to me.２．表示请求或个人的想法、看法，使语气婉转，有“愿、倒”等意思，例如：1) Would you please take a seat?2) Would you mind opening the window?3) I would like to express my thanks to you.３．表示过去习惯性的动作，着重动作的重复，有“总是、总会”等意思。

例如：On Sundays he would come to our village and work with us.４．表示虚拟、假设、条件等，有“要、将要、会、就会”等意思。

例如：1) If you had come earlier ,you would have seen him.2) It would be better to adopt the new method.[示例]考题１It is nearly seven ,Jack ____ be here at any moment. (NMET1995)A. mustB. NeedC. ShouldD. can解析这是带与语境的句子，从第一句的句意，我们便可以了解到＊第二句属推测句型，这样可排除选项Ｂ，在推测句型中否定句和疑问句中，故选Ｃ为正确，should 表示可能性的推测。

［训练］单项选择填空：1. ______read the letter for you?A. would you like meB. Do you want meC. will you mind meD. shall I2. He promised he ____not make such silly mistakes.A. wouldB. ShouldC. WillD. shall3. You are thirsty ,aren’t you? _____he get you some coffee?A. willB. ShallC. WillD. should4. You say you ____not do it ,but I say you _____ do it.A. will ;shallB. Shall ;shallC. Shall ;willD. will ;will5. ______your answer ,please? I didn’t quite catch you.A. should you repeatB. Are you doing to repeatC. will you repeatD. are you repeatingshould 用法should 一词在中学英语课本中出现频率很高。

它的用法灵活、含义丰富，因而一直是历年高考关注的热点。

现将其具体用法分述如下：1. should 作为助动词shall 的过去式，可以在间接引语中与第一人称主语搭配，表示过去将来时间。

例如：1) The group leader announced that we should（= would）begin to work soon.小组长宣布：我们不久就开始工作。

2) A week ago, I told him that I should（= would）go to Beijing the next day.一个星期以前，我告诉他我第二天就去北京。

2. should 作为情态动词，通常用来表示现在或将来的责任或义务，译作“应该”、“应当”，这时它可以和ought to, be supposed to 互换使用。

例如：1) You should（= are supposed to ）complete your test in time.你们应该按时做完你们的实验。

2) You should（= ought to ）tell your mother about it at once.你应该立即把此事告诉你妈妈。

3. should 作为情态动词，可以用在条件状语从句中，表示语气较强的假设，译作“万一”、“竟然”，这时也可将should 置于从句之首，即将should 放在主语前面，而省略从属连词if .例如：1) If anyone should come, say I am not at home.= Should anyone come, say I am not at home. 万一有人来访，就说我不在家。

2) If it should rain tomorrow, I wouldn't go.= Should it rain tomorrow, I wouldn't go. 万一明天天下雨，我就不去了。

4. should 作为情态动词，可以表示谦逊、客气、委婉之意，译为“可…”、“倒…”。

例如：1) I should say that it would be better to try it again. 我倒是认为最好再试一试。

2) You are mistaken, I should say. 据我看，你搞错了。

3) He should expect their basketball team to win the match.他倒是希望他们的篮球队赢得这场比赛的胜利。

4) Should you like some tea ？你可喜欢喝茶？5. should 作为情态动词，可以用来表示意外、惊喜或者在说话人看来是不可思议的。

尤其在以why, who, how 等开头的修辞疑问句或某些感叹句中常常译为“竟会”、“居然”。

例如：1) How should I know it？我怎么会知道这件事？2) Why should you be so late today？你今天怎么来得这么晚？3) When I went out, whom should I meet but my old friend Xiao Li！当我出去时，想不到竟会碰见我的老朋友小李！4) I don't see any reason why he shouldn't be happy. 我不明白为什么他居然不愉快。