Language: grammar and vocabulary
Modals in the past
Use should have, must have, could have and might have to talk about what happened, or what did not.
Modals like must and should cannot take -ed, so they need help to talk about the past. English gets round this by putting have plus a past participle after them. Must becomes must have taken; should becomes should have taken. The modal keeps its meaning; the have plus participle moves that meaning backwards in time.
The pattern, once and for all
modal + have + past participle. Must have gone, should have written, could have seen, might have forgotten. The have never changes, whoever the subject is: he must have gone, they must have gone.
Must have — concluding
The plates are washed, so somebody must have been here. You are not reporting what you saw; you are reasoning from evidence to a conclusion you are almost sure of.
Should have — the road not taken
You should have told me. This usually carries a second meaning: it did not happen. That is why it sounds like a criticism even when no criticism is intended.
Could have and might have — possibility
Could have says the chance existed: we could have won. Might have is a guess with more doubt in it: she might have missed the bus. Neither one claims to know.
Watch out
In quick speech, have shrinks until it sounds like of, and "should of" gets written down. It is never right. The word is have, however it sounds.
Worked example
Choose the past modal: "The window is broken and the ball is in the garden — somebody ____ it."
Ask what the speaker is doing. There is evidence, and a conclusion is being drawn from it.
That rules out should, which is about what ought to have happened, not about what did.
Try it together
Three situations, three past modals.
Each step names the modal you need. Write only the two words that fill the gap.
1.Use the past form of "must". Write two words: The pitch is soaked, so it ____ rained in the night.
Have a go
Which sentence says that something did not happen, and that it ought to have?
Ready to practise?
Eight questions on what you have just read. Nothing is timed, and you can play as many times as you like.