The document compares and contrasts the uses of modal verbs such as must, should, may, can, could, would and their past tense forms. It explains that modal verbs are used to express degrees of certainty or possibility about present and past actions. For example, "must" expresses certainty about the present while "must have" expresses certainty about the past. It provides examples to illustrate the different uses of each modal verb.

1. COMPARE THE SENTENCES MUST MUST HAVE Do you know where Tom is? I need to talk to him. Well, it's 8 o'clock. He be at home. must Do you know where Tom is? I can't see him anywhere. Oh, he left. must have I've seen him wearing his coat.

2. Must + base form certainty that something is true - He MUST be at home. Must have + Past participle certainty or logical conclusion about a past action - He MUST HAVE left.

3. COMPARE sooner than you expect They could contact you should/ought to your e-mails. She invited everyone should/ought to have Why didn't she invite me to the party? last week You read your e-mails. You read

4. Should/Ought to + base form advice/ suggestion You SHOULD/OUGHT TO read your e-mails Should have/Ought to have + past participle You SHOULD/OUGHT TO HAVE read your e-mails a criticism or regret about a past event Something you should do Something you should have done but you didn't

5. COMPARE You tell him. He could get angry. shouldn't You told him. shouldn't have He is angry now. SHOULDN'T + BASE FORM SHOULDN'T HAVE + PAST PARTICIPLE ADVICE CRITICISM OR REGRET ABOUT A PAST EVENT Something you shouldn't do Something you shouldn't have done but you did

6. COMPARE How will she get here? I don't know, actually. She take the bus. may/might Why is she so late? She taken may/might have the wrong bus

7. May/Might + May have/Might have+ past participle base form a guess about the future, a possibility in the future a guess about a past action, a possibility in the past She MAY/MIGHT take the bus She MAY/MIGHT HAVE taken the wrong bus

8. COMPARE Be careful! You hurt yourself could It was a stupid You hurt yourself could have thing to do.

9. Could + base form Possibility that something could happen, could be done You COULD hurt yourself Could have + past participle Possibility that something could have happened, but it didn't happen Possibility that something could have been done, but it wasn't done You COULD HAVE hurt yourself

10. Eric broken the vase He wasn't at home Eric broken the vase. He was at home Certainty that something has happened must have can't have Certainty that it is impossible that something happened

11. I called him, but I would have didn't have my mobile Would have + past participle Something I would have liked to do but I didn't because of something not depending on my willingness

12. SEE ALSO... Would + base form present conditional Would have + past participle past conditional