Past Modals come in two forms. 

The first type is the easiest and usually requires only a simple word change:


                                    Present Ability                                            Past Ability

                                I can drive.                                            I could drive when I was 16.

                                   Present Obligation                                      Past Obligation

                                I have to go to the City.                         I had to go to the City.

                                   Future Intention                                         Future Reported from Past

                                Lenny will pay tomorrow.                      Lenny said he would pay tomorrow.


Past Modals with have

Some PAST MODALS can be formed by using "have"+ the past participle of the main verb immediately after the modal. ("should have", "could have","would have", etc.)


However, since modals express possibility, intention, obligation, etc., they do not always indicate a definite tense. Therefore, when using past modals with have, special meanings need to be considered.



I should go to the funeral.  (I feel an obligation to go--later.)

I should have gone to the funeral.  (I didn't go. Now I regret it.)

Joe might take Karen to the airport.   (It's a future possibility.)

Joe might have taken Karen to the airport.  (He may be on his way there now.)

Joe could have taken Karen to the airport.  (Most likely he didn't.)

Joe would have taken Karen to the airport, but...  (He didn't. He had an excuse.)

Otis didn't come to work yesterday.  (Past fact)

He had to take care of his children.  (Past obligation)

His children must have been sick.  (Conjecture about the past)


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