may can would should的用法和意思
1）表示能力，could主要指過去時間。
Two eyes can see more than one. 兩只眼比壹只眼看得清。
Could the girl read before she went to school? 這女孩上學前能識字嗎？ 2）表示可能（理論上或是邏輯判斷上）。
The temperature can fall to –60℃, that is 60℃ below freezing. 氣溫可降至—60℃，也就是零下60℃。 He can?t (couldn?t) have enough money for a new car. 他不可能有足夠的錢買新車。 You mustn?t smoke while you?re walking around in the wood. You could start a fire.
在林子裏走時勿吸煙，那樣可能會引起火災。 3）表示允許。
Can I have a look at your new pen? 我可以看壹看妳的新鋼筆嗎？ He asked whether he could take the book out of the reading—room. 他問他可不可以把書帶出閱覽室。
4）表驚異、懷疑、不相信等態度。主要用於否定句、疑問句或感嘆句中。 Where can (could) they have gone to? 他們會去哪兒了呢？ He can?t (couldn?t) be over sixty. 他不可能超過六十歲。 How can you be so careless? 妳怎麽這麽粗心？ 5）比較委婉客氣地提出問題或陳述看法。
Can (Could) you lend me a hand? 幫我壹把好嗎？ I?m afraid we couldn?t give you an answer today. 恐怕我們今天不能給妳答復。
2. may (might)
1）表允許，might可以指過去時間，也可指現在時間，語氣更委婉。 You may take whatever you like. 妳喜歡什麽就拿什麽。
He told me that I might smoke in the room. 他告訴我可以在房間裏抽煙。 May (Might) I ask for a photo of your baby? 我可以要壹張妳寶寶的照片嗎？ 在回答以may引起的問句時，多避免用這個詞，而用其它方式，如Yes, please. / Certainly. / Please don?t ./ You?d better not. / No, you mustn?t.等，以免顯得太嚴峻或不客氣。
2）表可能（事實上）。可以指過去時間，也可以指現在時間，但語氣更加不肯定。
He may be at home. 他可能在家。
She may not know about it. 她可能不知道這件事。
He was afraid they might not agree with him. 他擔心他們可能不同意他的意見。 They might be having a meeting, but I?m not sure. 他們有可能在開會，不過我不肯定。
3. must
1）表示義務。意為―必須‖（主觀意誌）。
We must do everything step by step. 我們壹切都必須循序漸進地做。 You mustn?t talk to her like that. 妳不可能那樣對她說話。
--Must we hand in our exercise—books now? 我們現在就要交練習本嗎？ --No, you needn?t. / No, you don?t have to. 不必。（這種情況下，壹般不用mustn?t）
2）表示揣測。意為―想必、準是、壹定‖等，只用於肯定句。 He must be ill. He looks so pale. 他準是病了。他的臉色蒼白。 She?s wearing a diamond necklace. She must have a lot of money. 她戴著鉆石項鏈，壹定很有錢。 4. shall
1）表征詢意見，用於第壹、第三人稱疑問句。 Shall I get you some tea? 我給妳點茶好嗎？
Shall the boy wait outside? 讓那男孩在外面等嗎？ What shall we do this evening? 我們今晚做什麽？
2）表說話人的意願，有―命令、允諾、警告、決心‖等意思，用於第二、第三人稱陳述句。
You shall do as I say. 按我說的做。（命令）
You shall have my answer tomorrow. 妳明天可以得到我的答復。（允諾） He shall be sorry for it one day, I tell you. 有壹天他會後悔的，我告訴妳。（警告）
Nothing shall stop us from carrying out the plan. 什麽也不能阻止我們執行這項計劃。（決心）
5. will
1）表意願，用於各種人稱陳述句。
I will do anything for you. 我願為妳做任何事。 None is so blind as those who won?t see. 不願看的人眼最瞎。 If you will read the book, I?ll lend it to you. 如果妳願意讀這本書，我會把它借給妳。
2）表請求，用於疑問句。 Will you close the window? It?s a bit cold. 請妳把窗戶關上好嗎？有點冷。 Won?t you drink some more coffee? 再來壹點咖啡好嗎？ 3）表示某種傾向或習慣性動作。
Fish will die out of water. 魚離開水就不能活。 The door won?t open. 這門打不開。
The boy will sit there hour after hour looking at the traffic go by. 那男孩常常坐在那裏好幾個鐘點，看著車輛行人通過。 6. should
1）表義務。意為―應該‖（某件事宜於做），用於各種人稱。 You should be polite to your teachers. 妳對老師應該有禮貌。 You shouldn?t waste any time. 妳不應該浪費時間。 2）表推測，意為―想必壹定、照說應該、估計‖等。
The film should be very good as it is starring first—class actors.
這部新電影是壹流演員主演的，估計拍得很好。
They should be home by now. 照說他們現在應當已經到家了。 7.would
1）表意願。
They would not let him in because he was poorly dressed. 他們不讓他進去因為他衣著破舊。
I said I would do anything for you. 我說過我願意為妳做任何事。 2）表委婉地提出請求、建議或看法。
Would you like another glass of beer? 再來杯啤酒好嗎？
Would you mind cleaning the window? 請把窗戶擦壹下好嗎？ They wouldn?t have anything against it. 他們不會有什麽反對意見。 3）表過去反復發生的動作或過去的壹種傾向。
Every time she was in trouble, she would go to him for help. 她每遇到麻煩都會向她求助。他告訴我盒子打不開了。
（二）情態動詞後跟完成式和進行式的用法
1.情態動詞後跟完成式，表―應當已經……‖，―想必已經……‖，―本來可以……‖等意。
I should have finished the work earlier. 我應當早壹點完成這項工作的。 He isn?t here. He must have missed the train. 他還未到，壹定是沒趕上火車。 Where can (could) he have gone? 他能到那裏去了呢？
You may (might) have read about it. 妳可能在報上已經讀到這件事了。 You could (might) have been more careful. 妳本來可以更細心的。 He needn?t have worried about it. 他本不必為此事擔心。 There was a lot of fun at yesterday?s party. You ought to have come, but why didn?t you?
昨天的聚會非常有意思。妳本應該來，為何不來呢？
2. 情態動詞後跟進行式，表示―想必正在……‖，―可能正在……‖，―應當正在‖等意。 It?s twelve o?clock. They must be having lunch. 現在是十二點。他們壹定正在吃飯。
They may be discussing this problem. 他們可能正在論討這個問題。 He can?t be telling the truth. 他說的不可能是真話。 She shouldn?t be working like that. She?s still so weak. 她不應當那樣幹，她身體仍那麽虛。
（三）幾組詞的辨異 1. can 和be able to
1）情態動詞can只有兩種時態形式，現在式can和過去式could，而be able to有多種時態形式。
Mary can play the piano. She has been able to play it since she was 5. 瑪麗會彈鋼琴。她五歲起就會彈了。
2）用在過去時中，could經常表示能夠做某事，事實上不壹定去做，而was∕were able to則表示―過去做成了某事‖。在否定句中兩者可通用。 He could swim across the English Channel. But he didn?t feel like it that day. 他能遊過英吉利海峽，但那天他不想遊。
Yesterday I was able to get home before the heavy rain. 昨天我在下大雨前趕到了家裏。
2. must和 have to
must表示主觀意誌，而have to表示由於客觀因素不得不做某事。must沒有過去式，除在間接引語中可用於表示過去時間，在直接引語中表示過去時間應該用had to代替。
I told her that she must give up smoking. 我叫她必須戒煙。
We had to get everything ready that night. 我們那晚得把壹切準備就緒。 3. would和used to
1）used to表示過去與現在或過去某時與後來的情況有不同，而would只表過去的情況。
People used to think that the earth was flat.
過去人們認為地球是平的。（現在人們不這麽認為。）
She would go out for a walk in the morning when she was in the country. 在鄉下時，她總是在早晨去散會兒步。（可能現在仍有散步的習慣。）
2）used to可表示過去的習慣動作和經常的情況，而would只表示過去的習慣動作。
He used to ∕would smoke while writing. 過去他寫東西時常抽煙。 She used to be fat. 她過去很胖