2.1.- Modal verbs referring to the past (II).

There are several possibilities according to the different meanings of modal verbs.

1. Ability in the past.
   1. Could + have + past participle is used to express that someone had the ability to do something in the past but he did not do it.
      1. They could have continued with their studies but they preferred to start working.
      2. He could have learnt easily. Now he is nearly deaf.

• Advice in the past.
  • We use should + have + past perfect to say that someone did something wrong in the past. Sometimes we express the opposite.
    • He is upset because we didn't accept his invitation. We should have gone to his party. (We did wrong not accepting his invitation).
    • You should have stopped eating so many cakes two years ago.(You did wrong when you continued eating so many cakes).  
• Possibility in the past.
  • May/could/might + have + past participle are used to express that someone had the possibility in the past to do something.
    • Where was Peter last weekend? I don't know, he may have been at her parents' house.
    • Don't do that again. You could have fallen down. 
• Deduction in the past.
  • These two structures are used to express deductions about the past:
    • Must have + past participle. Where is Kate? I am not sure, but she must have gone to see her grandparents.
    • Can't have + past participle. "Long fingers" can't have robbed the bank because he was in prison at that time. 
• Absence of obligation in the past.
  • Needn't + have + past participle is used to express that someone did something in the past, but it was not necessary.
    • She needn't have bought so many bottles of wine. Nobody liked wine in the party. (It was not necessary to buy so much wine, but she did).