Modal verbs: past

1.       Had to:

•         Had to is the past form of must and refers to a past obligation

Sorry I’m late, I had to post some letters

•         The negative form is didn’t have to and refers to an absence of obligation

2.       Should have and ought to have:

•         Expectation; Should have refers to something which was supposed to happen

The parcel I sent you should have arrived by now

•         Criticism of an action

You shouldn’t have eaten so much last night

•         With be and adjectives describing chance

It was strange that you should have been staying in the same hotel last year

•         As a polite expression of thanks on receiving a gift or a favour

I’ve done the washing up for you. – Oh, you really shouldn’t have!

3.       Could have:

•         Could have refers to past possibility or uncertainty

It could have been Sue, I suppose (uncertainty)

•         Couldn’t have can be used with comparative adjectives

We couldn’t have been happier in those days

•         Could have can also express unwillingness

She could have gone to the party with her friends (but she didn’t)

4.       Could:

•         Could refers to past permission or past ability

Mary could swim when she was three

5.       May have and might have:

•         Might have refers to past possibility which did not happen

You might have drowned!

•         Might have and may have refer to uncertainty

I suppose I may have been rather critical

•         Both can be used in the negative to express uncertainty

They might not have received our letter yet

•         Might have is used to express annoyance at someone’s failure to  do something

You might have told me my trousers were split!

6.       Must have and can’t have:

•         These refer to the speaker’s certainty about a past action

You can’t have lost it (I am sure you didn’t)

•         Both can also be used with surely in exclamations

Surely you must have noticed it!

7.       Would not:

•         This expresses an unwillingness in the past

Everyone was angry because Sam wouldn’t turn off the television

8.       Would have:

•         Would have can refer to events in the past which did not actually happen

I would have accepted this job, but I didn’t want to move house

•         Assumptions about the past are also possible with would have

A: Someone called after you left but didn’t leave a message

B: That would have been Cathy, probably

9.       Needn’t have and didn’t need to:

•         Needn’t have refers to an unnecessary action which was actually done

You needn’t have paid all at once (you did pay)

•         Didn’t need to refers to an unnecessary action which was not done

I didn’t need to go to the dentist again, luckily