Expressing Possibility and Deduction

1.1 Use «must» to express a strong assumption when you’re sure something is true. Use «can’t» to express a strong assumption when you’re sure something is not true.

Examples

She must be very tired after working all night.(You're sure she is tired.)

He can't be over 30; he looks too young. (You're sure he is not over 30. NOT He mustn’t be over 30.)

You haven’t eaten all day. You must be hungry. 

You’ve just had lunch. You can’t be hungry. (NOT You mustn’t be hungry.)

1.2 Use «may (not)», «might (not)» and «could» to talk about what is possible or likely in the present or future.

Examples

This could be Maria’s house. 

It might rain tomorrow. 

Jack could (may) be at the party, I’m not sure.

She might not like that skirt. It’s not her style.

He doesn’t answer. He might be at the airport. He might be onboarding now.

1.3 Use «should» to talk about something that is likely to happen or something that is expected.

Examples

She should be here any minute. (It is likely she will arrive soon.)

The plan should work if we follow it correctly. (It is expected that the plan will succeed.)

1.4 Use «must», «can’t», «could/couldn’t», «may (not)», «might (not)» + have + past participle to speculate (make guesses) about the past events based on evidence. Use «must» when you are certain that something is true, and use «can’t/couldn’t» (not «mustn’t» when you are certain that something is not true.

Examples

He must have made a mistake. (You are sure he made a mistake based on the situation.)

You must have spoken to my brother. (You are sure of it because of something said.)

You can’t have talked to my brother, because he is not here. (You are sure it is impossible.)

They couldn’t have known about the change in schedule. (It was impossible for them to know.)

1.5 Use «could» + have + past participle to express something that was possible in the past but didn’t happen.

Examples

They could have died in that accident. (It was possible, but it didn’t happen.)

You could have won the game. (It was possible, but it didn’t happen.)

1.6 Use «may (not)», «might (not)» or «could»+ have + past participle when you aren’t sure that something is true or not.

Examples

She might have forgotten about the meeting or she could have got caught in the traffic. 

She might have caught a different flight. 

She may not have left work yet.

1.3 Use «should (not)» + have + past participle to express regret, a missed opportunity, or disapproval about something that didn’t happen or happened

Examples

I should have gone to bed earlier last night. (Regret about not doing it.)

You shouldn’t have bought that expensive phone.(Disapproval about what happened.)

1.1 Use «It’s (un)certain/(im)probable/(im)possible/(un)likely» + that-clause to express degrees of likelihood or possibility. It’s + adjective + that + complement clause.

Examples

It’s unlikely that she’ll be home on time.

It’s possible that we’ll finish early.

It’s improbable that he’ll accept the offer.

It’s certain that the project will succeed.

1.2 Use «subject + be + certain + to + base verb» to express a high degree of certainty about a future event or action. Use «(un)likely + to + base verb» to express (im)probability of an event or action.

Examples

He’s certain to pass the exam. 

They are certain to succeed in their new venture.

The train is likely to be late.

It’s likely to rain this evening.

She’s unlikely to win the competition.

1.3 Use «due to + base verb» to refer to events or actions that are expected at a specific time or are scheduled to happen.

Examples

The guests are due to arrive at 7 p.m.

The plane is due to take off in 30 minutes.