Do you know how to use modal verbs and other expressions to show how certain or uncertain you are about something? Enhance your knowledge with a lesson given below and the grammar explanation to guide you better.

Check out these examples to see how modal verbs and expressions are used to show the speaker’s level of certainty:

• He could easily be at the office right now.

• That has to be her sister.

• That can’t be true.

• You're likely to forget things from time to time.

Grammar explanation - Modals: probability

Here is the explanation to help you understand:

1. Certainty

a) must

We use must when we are confident that something is true or believe it's the only logical possibility.

• You must be exhausted after working a double shift.

• That must be Maria's office. Her name is on the door.

Note that must shows that we have reasoned this conclusion from evidence or logic.

• This must be the restaurant. (I've concluded this based on evidence or reasoning.)

• This is the restaurant. (A simple factual statement.)

b) be bound to

We use be bound to to express certainty about a future event or prediction.

• With all this rain, the event is bound to be canceled.

• They’ve been training hard – they’re bound to win the championship.

• Be bound to is not a modal verb, but it's used in a similar way.

c) can't

We use can't when we are certain that something is not possible.

• That can't be the answer; it doesn't make sense.

• He can't have finished already; it's only been ten minutes.

2. Degrees of uncertainty

a) should/shouldn't

We use should and shouldn't to indicate expectations about the future. They suggest that something is likely because it's normal or reasonable to expect it.

• Rest up and take medicine. You should feel better by tomorrow.

• It shouldn't take long to fix the issue.

Should and shouldn't here imply "if everything goes well." We don't use them for predicting negative or unpleasant situations.

• The meeting should be very uncomfortable. (Incorrect)

b) might, may, could

We use might, may, or could to express that something in the present or future is possible, but we're not certain.

• I might visit the park tomorrow if the weather's nice.

• There may be more details we're missing.

• This issue could be resolved quickly.

All three have the same meaning, but may is more formal than might or could.

Adding well after the modal verb makes the situation sound more likely.

• I’ll try calling again, but it might well be too late.

• She may well decide to take a different job.

• That could well be the case.

The negative forms are may not and might not (or mightn't).

• We may not need umbrellas, but I'll bring one just in case.

• Jake might not attend the meeting as he's traveling today.

Couldn't is different from may not and might not; it means that something is impossible.

3. General possibility

a) can

Can is not used to describe the possibility of a specific event or situation.

• Alia may/might/could be in the garden. (Not: Alia can be in the garden.)

• Instead, can is used to show that something sometimes happens or has the ability to happen.

• Traffic can be terrible during rush hour.

• It can get really hot here in the summer.

Note that all modal verbs are followed by an infinitive without to.

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