Modal verb

情态动词（Modal verb），本身有一定的词义，表示语气的单词。但是情态动词不能独立作谓语，只能和动词原形一起构成谓语。情态动词用在行为动词前，表示说话人对这一动作或状态的看法或主观设想。 情态动词的含义虽然数量不多，但用途广泛，英文中常见的有： can (could), may (might), must, need, ought to, dare (dared), shall (should), will (would)。

Modal verb

• 表推测
  • 现在的推测
    • 一般状态
      • 情+do
        • 肯定句:must(一定) > can/could(有时候可能) > may/might(微乎其微)
          • He must be heart-broken.
          • The teacher can make mistakes sometimes.
          • I buy a lottery ticket. And I might win 500 million dollars.
        • 否定句:can’t/couldn’t (不可能)>may not/ might not(可能不)
          • It can’t be true!
        • 疑问句:一般只用can/could
          • Could this be love that I feel?
    • 正在进行
      • 情+be doing
        • He must be sleeping.他一定睡着了
    • 过去
      • must have done 过去一定做……
        • The ground is wet. It must have rained last night .
      • may/ might have done 过去可能做……
        • Xiaoming may/ might have played computer games last night.
      • can’t have done 过去不可能做……
    • 将来
      • 情+do
• 表许可
  • can, could, may, might
    • 疑问句
      • can最常用
        • Can I have some popcorn? Yes,you can.
      • could用正式场合或和陌生人谈话,语气更委婉
        • Excuse me ,could I sit here,please?
      • May/might 用正式场合
        • May I make an appointment?
    • 肯定句
      • Yes, you may borrow my pen.
      • Sure, you can borrow my pen.
    • 表拒绝请求
      • Can/could I borrow your pen?No, you can’t borrow my pen.
      • May/Might I borrow your pen?You may not borrow my pen.
        • may not 表示不许，一般不用于拒绝他人请求
• 表可能
  • can, could, may, might
    • may、might表示现在或将来的可能
      • 事实上
      • It may/might be ture.
      • He may/might leave tomorrow.
    • can
      • 逻辑上
      • 用于疑问句
        • Where can he be?He may be in the office.
      • 用于否定句
        • It can't be ture.
    • 过去的可能
      • may/might+have done/have been doing
        • He may/might have missed the train.
        • We may/might have been indulging in an illusion.
      • can/could+have done
        • He can/could have missed the train.
    • might/could+have done
      • 表示本来可能发生但没有发生的动作
        • 完成性较低
        • You might have killed yourself .你差点儿送了命。
      • 表示本来可能完成却没有完成的动作
        • I could have reported you.我本可以告发你。
  • 表示很大的可能性
    • probable、probably、likely、probability、likelihood等
      • It is probable/likely that he will come.
      • He is likely to come.
• 表能力
  • 过去的能力
    • could、was/were able to
      • 肯定句中could泛指过去的一般能力，表示过去做某件具体事情的能力不用could，否定句没有限制
      • when I was a student, I could study all night before an exam.
  • 现在的能力
    • can, be able to
      • Bob can swim well.
  • 将来的能力
    • can, will be able to
      • I will be able to speak German in another two months.
• 表建议
  • should, ought to，had better
    • Should, ought to表示建议或劝告某人“应该”做某事
      • You should/ought to give up smoking.你应该戒烟了。
      • Should have done本应当做某事
      • I’m surprised that such a gentle man should be so rude to the old.
        • 居然，竟然
    • had better用于给出强烈或紧急的建议，表示如果不听从建议的话会带来严重后果
      • You had better not miss the last bus.你最好不要误了最后一班公共汽车
  • Shall
    • 用于第一，第三人称的疑问句中
      • Shall we take a rest?
  • had better
    • 用于给出强烈建议
• 表义务
  • 表示现在的必须
    • must, have to 表示有必要或义务做某事
      • You must/have to be back before 10 o’clock.你必须十点前回来。
  • 表示过去的必须
    • had to
      • I had to leave at six yesterday.
  • don't have to表示不需要做某事
    • You don't have to use a calculator,but it might be useful.
  • must 的否定形式
    • must not/mustn't表示禁止做某事
      • You must not use a calculator during this exam.
    • need not/needn't表示不必做某事
      • You needn't do it at once.
• 表意愿、决心
  • Will/would 表示意愿（willingness) 即愿意做某事
    • -Will/ would you please help me?Yes, I will
      • 表示客气请求时用would you, 但回答时用will, 不用would
  • 表示过去的“意愿”或过去不愿意做某事，用would ，would not
    • I asked him if he would help me with my writing.
  • Will/would 表示决心（determination) 即坚持做某事
    • I will take the job and no one is going to stop me.
      • am determined to
    • She would marry him in spite of my warning that it was unwise.
      • Insisted on marrying him
• 表示警告，威胁，命令，允诺
  • Shall
    • 用于第一，第二人称的陈述句中
      • You shall be punished if you break the rule.警告
      • You shall obey my rules.命令
      • You shall have the book when I finish it.允诺
    • Shall 的否定形式shall not, shan’t 表示“禁止”，“威胁”
      • Visitors shall not pick out flowers.
• Would/should/could/might+have done-虚拟
  • could have done本能够做却没做
    • I could have told you the answer, but you didn't ask me.
  • Should have done本应该做却没做
    • You should have come earlier.
  • might have done推测/虚拟
  • need have done本需要做却没做