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Degrees of Certainty: Past Time
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Degrees of Certainty: Past Time
Perfect Modals
50% Positive
Student A: Why wasn't Maggie in class yesterday?
Student B: I don' know. She might have been sick, or she may have slept late.
Student A: Hmm, well I hope she is okay.
If you are not sure or you are just guessing, use the following strucutre:
may + have + past participle
might + have + past participle
could + have + past participle
95% Positive
100% Positive
Student A: Why wasn't Maggie in class yesterday?
Student B: She must have been sick. I heard a student say something about her being at the hospital with a high fever.
Student A: Oh, I hope she is okay.
100% Negative
Student A: Why wasn't Maggie in class yesterday?
Student B: Oh, She was sick.
Student A: How do you know? Did you talk to her?
Student B: Yeah, I saw her at the hospital last night.
Student A: Why wasn't Maggie in class yesterday?
Student B: Well, I know she wasn't sick because I saw her at the coffee shop yesterday morning.
Student A: That is unusual. She hardly ever misses class.
99% Negative
Student A: Why wasn't Maggie in class yesterday?
Student B: Well, she couldn't have been at school because she did not attend any of her classes.
Student A: True.
When you are almost positive that at least this is true, use the following structure:
could not + have + past participle
can not + have + past participle
When you are positive that it did NOT happen, use the negative form of V-be.
95% Negative
Student A: Why wasn't Maggie in class yesterday?
Student B: She must not have felt well. She was coughing in class the day before yesterday.
Student A: Oh yeah, that makes sense.
50% Negative
Student A: Why wasn't Maggie in class yesterday?
Student B: She may not have felt well, or she might not have woken up in time.
Student A: Hmm, well I hope she is okay.
If you are pretty sure you know the negative answer, use the following structure:
must not + have + past participle
If you are not sure in the negative form, use the following structure:
may not + have + past participle
might not + have + past participle
Regret / Advice for the Past
Student A: Oh, no! I failed this quiz. I guess that is what I get for not studying.
Student B: Yes, you should have studied more. These quizzes are challenging.
Student A: You are right.
For expressing past regret or offering advice for something that has already happened, use the following structure:
should + have + past particple
If you are almost 100% sure, use the following structure:
must + have + past participle
When you are positive, just use V-be.