Modal perfect

Modal + have + past participle is used to guess about or judge something that already happened. have never changes — it is never has or had, whatever the subject.

💡In speech, have almost disappears: must've /ˈmʌstəv/, should've, could've, might've — it sounds like “must of”. When you write, always write have, and after have use the past participle (gone, seen), not the past simple (went, saw).

Choose the modal by how sure you are:

• Nobody's answering. They must have gone out.

• I may have left my wallet in the taxi.

• Minh can't have written this — he doesn't speak French.

• She couldn't have known about the party. We kept it secret.

The negative of must have (when guessing) is usually can't have / couldn't have. American English also often uses must not have + V3 for “I'm sure it didn't happen” (He must not have seen me), but the short form mustn't have is rare. Note that couldn't have (impossible) is much stronger than might not have (maybe not).

The same modal: + base verb is about now, + have V3 is about the past. See the lesson “Deduction: must / can't”.

should have + V3 = it was the right thing to do (but it didn't happen); shouldn't have + V3 = it was wrong (but it happened). We use it for regret or criticism. ought to have means the same but is less common. should have can also mean “by now, as expected, …”.

• We should have booked a table — the place is full.

• You shouldn't have said that to her.

• You ought to have asked before borrowing my bike.

• The parcel should have arrived by now.

  as expected

• could have + V3: it was possible, but it didn't happen; also a mild complaint (You could have told me!).
• couldn't have + comparative: it couldn't have been better / worse.
• would have + V3: you were willing or ready to do it, but something stopped you.
• needn't have + V3 (mainly British): you did it, but it wasn't necessary. Compare didn't need to + verb: it wasn't necessary, so (usually) you didn't do it.

• I could have gone to university, but I chose to work.

• You could have told me the meeting was cancelled!

  a mild complaint

• We couldn't have asked for better weather.

• I would have called you, but my phone died.

• You needn't have cooked so much — there are only four of us.

  you already cooked it

• I didn't need to cook — we ate out.

  so I didn't cook

• ✗She must has forgotten our meeting.

  ✓She must have forgotten our meeting.

  After a modal it is always have.

• ✗You should have went to bed earlier.

  ✓You should have gone to bed earlier.

  have + past participle, not past simple.

• ✗I should of told you earlier.

  ✓I should have told you earlier.

  should've sounds like “should of”, but it is have.

• ✗He can't have saw the message.

  ✓He can't have seen the message.

  can't have + past participle.

• ✗She should have been arrived by now.

  ✓She should have arrived by now.

  arrive is active — no been.

• ✗I must have left my keys at home, but I'm not sure.

  ✓I might have left my keys at home, but I'm not sure.

  Not sure → might / may / could have.