Modals

Modal Verbs

Present & Future

Must = ‘internal’ obligation
Have to/don’t have to = ‘external’ obligation
No obligation e.g. you don’t have to insure your car for theft.
Need to/needn’t or don’t need to = weaker obligation

Must not = negative obligation e.g. you mustn’t speak to your father like that!

Should/ought to = advice, duty


Past Modals


Should / shouldn’t have + PP

= (1)criticize past actions
e.g. you should have bought the milk!

= (2)to talk about events that you expect/were supposed to happen.
e.g. I should have done a test today, but I was ill.


Must/ mustn’t have + PP = very strong deduction/possibility e.g. She mustn’t have passed the exam, she is upset.

Had to = past obligation
e.g. I had to pay lots of tax last year.(external obligation)
We had to wash the car, it was very dirty.(internal obligation)

Will have to = future obligation

Couldn’t or wasn’t/weren’t allowed = past prohibition
e.g. I couldn’t use my ID card for travelling.


Needn’t have + PP = action completed, but wasn’t necessary e.g. I needn’t have hurried because the lesson started late.

Didn’t need to + inf = action (performed or not) wasn’t necessary
e.g. I didn’t need to hurry because I was early.

Can, could, be able to = ability

Past (positive): could = general ability e.g. I could never understand my teacher when she spoke.
Was/were able = specific instances of ability e.g. I was able to finish the race.
Past (negative): wasn’t/weren’t able to/couldn’t, have same meaning.