Have you ever wondered how to express certainty, possibility, or advisability about past events? In English Dialogue: Expressing Past Probability With Modals + Perfective, you have noticed the use of modals + perfective in English conversation to express certainty, possibility, and advisability in the past. Look at the following phrases:
- ... must have forgotten ....
- ... might have lost ....
- ... may have left ....
- ... should have been ....
Structure of "Modals + Perfective"
Subject | Modals | have | past participle |
---|---|---|---|
I We You They He She It Etc. | may might ought to must could should would | have | been slept arrived finished forgotten left gone Etc. |
Question words | Modals | Subject | have | past participle |
---|---|---|---|---|
Who What How Where When Etc. | may might must could should would | I we you they he she it Etc. | have | been? slept? arrived? finished? forgotten? left? gone? Etc. |
Subject | Modals + not | have | past participle |
---|---|---|---|
I We You They He She It Etc. | may not might not ought not to must not (mustn't) could not (couldn't) should not (shouldn't) needn't would not (wouldn't) | have | been slept arrived finished forgotten left gone Etc. |
Usage of "Modals + Perfective"
- May have + past participle ➡️ expresses less than 50% certainty.
Example: I may have left my umbrella in the coffee lounge. - Might have + past participle ➡️ expresses less than 50% certainty.
Example: I might have lost it anywhere. - Ought to have + past participle ➡️ expresses:
- advisability
Example: You ought to have talked to your manager, but you didn't. - 90% certainty/expectation
Example: She ought to have done well in the test because she was well prepared.
- advisability
- Must have + past participle ➡️ expresses 95% certainty/logical conclusion
Example: You must have lost your umbrella, not your briefcase. - Could have + past participle ➡️ expresses:
- less than 50% certainty
Example: I suppose someone could have picked it up before I rang. - unfulfilled suggestion (positive sentence only)
Example: You could have talked to me before making the decision. - impossibility (negative only)
Example: He couldn't have done such a silly thing.
- less than 50% certainty
- Should have + past participle ➡️ expresses:
- advisability/unfulfilled expectation
Example: He should have worked harder for the test, but he didn't. - 90% certainty/expectation
Example: She should have done well in the test because she was well prepared.
- advisability/unfulfilled expectation
- Needn't have + past participle ➡️ expresses lack of necessity.
Example: You needn't have worried all day. - Would have + past participle ➡️ talks about hypothetical or unrealized actions in the past. It often appears in third conditional sentences and regrets about past actions.
Example:- If she had left earlier, she wouldn’t have missed the train.
- She would have called you, but her phone ran out of battery.
Examples Sentences in Context
Practice these dialogues and pay attention to what the modal + perfective structures imply.Dialogue 1
Woman: "Yesterday I walked home from work because I didn’t have any money for the bus."
Man: "Oh, you didn’t have to walk home! I would have been happy to lend you some money."
Woman: "I didn’t want to trouble you."
Man: "Oh, but you could have just asked me — I’d have gladly helped."
Man: "Oh, you didn’t have to walk home! I would have been happy to lend you some money."
Woman: "I didn’t want to trouble you."
Man: "Oh, but you could have just asked me — I’d have gladly helped."
Dialogue 2
Man: "Why didn’t Sarah attend the meeting?"
Woman: "I don’t know. She must have forgotten about it."
Woman: "I don’t know. She must have forgotten about it."
Dialogue 3
Woman: "Why are they so late?"
Man: "They might have been stuck in traffic."
Man: "They might have been stuck in traffic."
Dialogue 4
Man: "I called you last night, but no one answered."
Woman: "Sorry, I must have been asleep."
Woman: "Sorry, I must have been asleep."

Practice Exercises
A. Multiple Choice Questions
Select the correct modal + perfective form to complete the dialogues below.- Tom: Where was Mary yesterday? She wasn't at work.
Bob: She ... sick yesterday. - Lucy: Betty wasn't home when I called.
Ann: She ... downtown. She had told me she had to do some shopping. - Andy: Bob was late for the meeting this morning.
Bill: He ... in a traffic jam. There was a serious accident on the highway. - Lisa: I didn't know that the meeting would be postponed to next week.
Mary: Yes. You ... the room today. - Hadi: I think I've lost my key. I put it in my pocket after locking the room.
Mary: You ... it somewhere. - Betty: He hasn't arrived yet. I assume he's gone the wrong way.
Rosa: I think so. He ... lost. - Jim: Nancy hasn't received the email.
Bill: Really? It ... to the wrong address. - Dave: Bella didn't call her office when she was away from work yesterday.
Gary: That was bad. She ... her boss. - Sam: I worked until late last night.
Greg: You ... so hard. The report is due next week. - Rea: Did she phone the police?
Lori: No. She ... them, but she didn't.
B. Modals in the Past Transformation
Rewrite the following sentences in the past using the modal + perfective form (modal + have + past participle). The first one has been done for you.- That must be a very interesting play.
That must have been a very interesting play. Now, rewrite the following sentences: - Joan may not remember the number.
Joan the number - John might forget to do the shopping.
John to do the shopping. - He needn't do that work.
He that work. - You could borrow my laptop.
You my laptop. - She should get to work on time.
She to work on time.
C. Sentence Completion
Complete the sentences with the correct modal + perfective form of the verb in parentheses.- She looks so tired. She all night.
- I can’t find my wallet. I it at the café.
- They didn’t answer my call. They to bed early.
- You me about your problem. Maybe I could help you.
- He was very late. He the bus.
- The meeting was canceled, so you all the way here.
- She got a high score. She well for the exam.
- There was no response. They the doorbell.
- You so much time yesterday.
- He more careful while driving.
D. Sentence Transformation
Rewrite the following sentences using modals + perfective.- It’s possible that she forgot to lock the door.
- I’m sure they misunderstood the instructions.
- It wasn’t necessary for you to bring your umbrella. The rain stopped.
- He didn’t study, but he was supposed to.
- Perhaps John took the wrong train.
- It was a mistake to spend so much money on a new phone.
- I’m sure she didn’t hear the alarm clock.
- It’s likely that they arrived late.
- She didn’t attend the meeting, but she should have.
-
There’s no way he finished the project in one day.
