We can use modal verbs to talk about possibility or to express uncertainty, and ‘might’ is the most common modal verb for such cases.

 

Statements with ‘might’ can refer to past, present, or future possibilities.

 

To refer to past possibility, use:

 

Might + have + past participle

 

I can’t find my pen. I might have dropped it earlier.

 

We are lost. We might have taken a wrong turn at the river.

 

To refer to present possibility, use:

 

Might + the base form of the verb

 

Look at Jack! He might be in a hurry to meet with Catherine.

 

The clouds cover the top of the mountain. It might be windy there.

 

To refer to future possibility, use:

 

Might + the base form of the verb + future time marker

 

It’s cold outside. It might snow later on.

 

Joe might not come to our party next weekend.

 

We can use modal verbs to talk about probability or improbability of something, as well as to make deductions about some facts or events.

 

To talk about something with uncertainty, use modal verbs ‘might’ and ‘could’:

 

Sarah isn’t feeling well. She might have a cold.

 

I have a high temperature. It could be a flu.

 

To describe negative things you are not certain about, use ‘might not’:

 

Your leg is not swollen, so it might not be serious.

 

I can’t reach Tom by phone, he might not be in the city.

 

To speak with more certainty about things in present, use ‘must’:

 

John must be very tired, he’s been staying in bed all day long.

 

They must be absent, I cannot find them anywhere.

 

To speak about something you consider absolutely impossible, use ‘cannot (can’t)’:

 

Jack cannot be at school, I saw him playing basketball at the playground.

 

Pete’s leg can’t be broken, he walked to the doctor without any help.

 

To speak about something that you think definitely happened in the past, use  ‘must have’ with the past participle (for regular verbs, this is the “-ed” form of the verb):

 

I can’t find my socks. My wife must have taken them to the laundry room.

 

Nobody opens the door, my friend must have left the house already.

 

In case you are not sure whether something happened in the past, use ‘may have’, ‘might have’ or ‘could have’ instead of ‘must have’:

 

Cindy didn’t return my call yesterday. She might have forgotten to call me back.

 

I didn’t see who knocked on the door, but it may have been the postman.

 

And finally, if you are absolutely sure that something did not happen in the past, use ‘couldn’t have’:

 

I saw a flash in the sky, but it couldn’t have been aliens, they don’t exist.

 

Paula couldn’t have been at the party last night, she was at work.

 

In negative statements ‘must’ and ‘have to’ are used differently.

 

‘Must not’ is a negative obligation, meaning that something is not allowed.

We form negative statements with ‘must not’ like this:

 

Subject + must not/ mustn’t + the base form of the verb without ‘to’:

 

Singular	Plural
I must not (mustn’t) speak You must not speak He/she/it must not speak	We must not speak You must not speak They must not speak

 

She must not take this medicine.

 

You must not smoke in the office.

 

‘Do not have to’ means there is no need to do something.

We form negative statements with ‘do not have to’ like this:

 

Subject + do not / don’t / doesn’t have to + the base form of the verb:

 

Singular	Plural
I do not (don’t) have to wait You don’t have to wait He/she/it doesn’t have to wait	We don’t have to wait You don’t have to wait They don’t have to wait

 

You don’t have to buy me a birthday present.

 

It’s summertime, and Peter doesn’t have to go to school.

 

We also use ‘have to’ in questions, for example, to ask if something is necessary. Such questions are formed like this:

 

Do/Does + subject + have to +the base form of the verb:

 

Singular	Plural
Do I have to speak? Do you have to speak? Does he/she/it have to speak?	Do we have to speak? Do you have to speak? Do they have to speak?

 

Do I have to get ready now?

 

Does she have to leave before 12 a.m.?

 

Note: ‘must’ is possible in questions (Must we finish this today?), but ‘have to‘ is more common.

 

To offer suggestions and give advice in English we can use ‘could’, ‘should’, ‘ought to’, ‘had better’.

 

‘Should’ is used when the speaker wants to make a strong suggestion:

 

The sun is shining bright, so you should wear a cap.

 

You look pale. I don’t think you should go to school today.

 

The road is wet. You shouldn’t drive too fast.

 

In more formal situations you can use ‘ought to’ instead of ‘should’, but this modal verb is not used in negative statements and questions:

 

You ought to (should) wear a scarf. It’s very cold outside.

 

They ought to hurry, their train is leaving.

 

Jane ought to visit that castle, it’s great!

 

If you want to give an important piece of advice or recommendation (that can have a negative consequence if not followed), use ‘had better’:

 

You had better (You‘d better) leave for work, it’s 8 o’clock already.

 

We‘d better go that way, we’ll save about 10 minutes.

He’d better park his car correctly or he will get fined.

 

Note: Had better is a strong expression. We use it if we think there will be negative results if someone does not do what is suggested.

 

‘Could’ is not as strong as ‘should’ and is normally used to give a mild advice or to suggest a solution to some problem:

 

– I hate my old jeans!

– Well, you could buy a new pair.

 

If they need more space, they could look for a bigger house.

 

Jack moves to Canada next month. He could learn to play hockey there.