育才分流英语语法词法精品辅导3情态动词、虚拟语气、非谓语动词名词性从句和定语从句情态动词【要点点拨】1.表示请求和允许：can,could,may,might.过去式使语气更委婉，答语应用原形。
---Could Iuse your computer tomorrow morning?---Yes,you can.(否定回答可用：No,I'm afraid not.)2.表示推测：理论可能性can可能性肯定句must,may,might,could疑问句can否定句can't(不可能)，may not(可能不)1)can表示理论上的可能性，指某事或情况可能发生，但并不说明实际上真的发生.Children can be very tiring.2)反意问句。
He may know the plan,doesn'the?You must have studied Englishbefore,haven'tyou?You can't have beencaught in the rain last night,wereyou?3.could&be able to在肯定句中could表示过去有"能力"做，was/were able to表示过去有能力而且确实做成了某一件事，相当于managed to do…或succeeded in doing sth.The fire spread through the hotel very quickly but everyone was able to get out.4.may/might as well do sth"还是…好"、"不妨"You might as well tell me the truth.你还是把真相告诉我的好。
5.must和have to 1)must表示的是说话人的主观看法,而have to强调客观需要。
2)否定形式含义不同。
mustn't禁止，不许可，don't have to不必3)must偏要(做令人不快的事)eg.Must you shout so loudly?6.shall和should 1)表示说话人征求对方意见和向对方请示，用于第一、三人称。
When shall my father be able to leave hospital?shall 2)表示说话人给对方的命令、警告、允诺或威胁以及说话人的决心。
You shall go with me(命令)/You shall have the book when Ifinish it.(允诺)He shall be punished(威胁)/Nothing shall stop me from doingit.(决心)1)表示劝告和建议"应该"2)"按道理应当""估计"(=ought to)They should be there by now,I think.3)用于第一人称表示说话人的一种谦逊、客气、委婉的语气。
I should advise you not do that.我倒是劝你别这样做。
Should 4)在条件句中表示"万一"，主句不一定用虚拟语气。
Ask Tom to ring me up if you should see him./Should Ibe free tomorrow,I'll come.5)Why/How+should结构表示说话人对某事不能理解，感到意外、惊异等意思，意为"竟然"，也用在某些从句中。
It seems so unfair that this should happen to me.这种事竟然发生在我身上真不公平。
7.will和would 1)表示意志和意愿。
will指现在，would指过去。
If you will listen to me,I'll give you some advice.2)表示请求、建议，would比will委婉、客气。
Will(Would)you please pass me the book?3)表示习惯性动作，"总是""惯于"，will指现在，would指过去。
Fish will die without water.Every evening,she would sit by the window,deep in thought.4).表示功能，意为"能"或"行"The machine won't work.5)表示预料或猜想。
It would be about ten when he left home.猜想他离开家时大约十点。
8.would&used to 1)表示过去持续的状态和情况用used to；would不与表示状态的动词连用。
There used to be ahospital here./There would be ahospital here.(×)2)would常与often,sometimes,for hours等表示时间的副词(短语)连用。
We would sit in the yard every evening and listened to his story.3)used to强调过去的行为同现在的对比，含有"过去怎样，而现在却不这样了"的含义.eg.He will not spend the money on books as he used to.9.dare和need两者作为情态动词都不用于肯定句，常用于否定句、疑问句和条件从句中。
习惯用语I dare say(可能，或许，我揣测)除外。
实义动词用法同于一般动词。
但在否定句中，dare后的to可省略，即：don't/doesn'tdare(to)do….need作为实义动词时，用在否定句中时，其后的to不能省略。
He dare go there alone.(×)He dares to go there.He dares not go there alone.(×)He dare not go there alone./He doesn't dare(to)go there alone.He stood there without daring lift his head.(×)He stood there without daring to lift his head.10.情态动词+have done,表示过去比较：情态动词+do,表示现在或将来。
cf.needn't have done&didn't need to do…She need not have come yesterday.她昨天本不必要来的。
(但却来了) She didn't need to come yesterday.她昨天不必来。
(实际上也没来) 虚拟语气【要点点拨】一：形式为(should)+v.1.宾语从句中。
一个坚持(insist),两个命令(order,command),三条建议(advise,suggest,propose),四项要求(demand,require,request,ask).还有prefer，advise等词。
注意：1)suggest和insist有例外The smile on his face suggested that he was satisfied with our work.("暗示""表明")The man insisted that he had never stolen the money.2)这类动词的名词形式后的表语从句和同位语从句中也要用(should)+v.形式。
另外，还有plan,idea等词。
2.主语从句中1)It is necessary/important/strange/natural/a pity/a shame/no wonder…that….eg.It is strange that he should have acted towards his parents like that.二：形式为在原本的时态上退一步，即"+过去"1.在条件句中的运用条件从句主句与现在事实相反过去式(be一般用were)would/could/might+v.与过去事实相反had+过去分词would/could/might+have+过去分词与将来事实相反1)过去式2)should+v.3)were to+v.would/could/might+v.(第一人称可用should,以上同)1)"混合虚拟条件句"或"错综时间条件句"主句和从句时间上不一致，从句可以和过去时间相反，主句可以与现在事实相反。
If you had taken my advice just now,you would be better now.2)if省略句。
在条件句中，可省略if,把were,had,should提到句首，变为倒装句式。
Were Iyou,I would seize the chance to go abroad.3)含蓄条件句A)with,without,but for等介词短语代替条件句But for the rain,the crops would have died.(=If it hadn't been for the rain)B)其他手段I was ill that day.Otherwise,I would have taken part in the sports meeting.(副词)He telephoned to inform me of your birthday,orI would have known nothing about it.(连词)I might have given you more help,butI was too busy.(连词)Given more time,we could have done it better.(分词短语)It would be amistakenot to help him.(动词不定式)2.宾语从句中wish,would rather后,但would rather后所跟句子跟现在、将来相反用过去时，跟过去时间相反使用过去完成时。