Modal Verbs Of Certainty, Probability and Possibility

Certainty

To express certainty in the present, we use must, can’tandcouldn’t.

To express certainty in the past, we use must have, can’t have and couldn’t have.

1. a)I can’t find my keys. They must be here somewhere because I used them to open the front door.
2. b)Theycan’t be outside, because I came inside immediately.
3. c)I must have put them back in my handbag. Oh yes here they are!

Probability

To talk about probability in the present or future, we use should and ought to.

1. d)Youshould bebetter soon if you take this medicine.
2. e)You ought to recover quickly if you follow the doctor’s orders.

To talk about it in the past, we use should have and ought to have.

1. f)My rash should have gone by now. I have been using this cream exactly as the doctor told me to.
2. g)I ought to have had a lower fever by now. I have been taking medication.

Possibility

We use could, may and might to talk about the possibility of something either in the present or in the future.

1. h)I think you should go back to the doctor. That rash could/may/might get worse, and you might have scars later.

We use could have and might have + past participle to talk about possibility in the past.

1. i)I could/might have died if I hadn’t gone to hospital when I did.

Exercise 1.- Grammar

Complete each sentence with one word.

1. a)They aren’t answering their phones. They ____________ be somewhere without a signal.

1. b)Elvis Presley_______________ be alive. Someone would have seen him by now.

1. c)The passengers on the flight _______________ if the pilot hadn’t reacted so quickly.

1. d)I don’t know why I’m still feeling ill. I took the medicine, so I _______________ feeling better by now.

1. e)She_______________ her keys in the car.

1. f)You _______________  He is on holiday in Australia.
2. g)The students _______________very nervous, which is why they didn’t do well in the exam.

1. h)She doesn’t know when she got home. She _______________so tired that she can’t remember.