Modals of speculation

Modal verbs of speculation

may

must

can’t

could

might

must

We use must + infinitive for obligation and strong recommendation, but also to say that we are quite sure that something is true.

EXAMPLES:

• They are almost identical. They must be sisters.
• But I answered all the questions correctly. There must be a mistake.

must

We use must be + –ing with dynamic verbs to say that we are quite sure that something is happening now.

EXAMPLES:

• What you are saying is not possible. You must be kidding.
• Can you hear the shouting? Our neighbours must be arguing again.

must

We use must have + past participle or must have been + -ing to say that we are quite sure that something was true or happened in the past.

EXAMPLES:

• I can’t find my mobile! I must have dropped it in the taxi.
• You must have had a real scare when you saw the crocodile.
• He was the only victim. He must have been sleeping when the fire started.

can’t

We can use can’t + infinitive to say that we are quite sure that something is NOT true.

EXAMPLES:

• He can’t be that famous. I’ve never heard his name before.
• She can’t be married. I have never seen a ring on her finger.

can’t

We use can’t be + –ing to say that we are quite sure that something is NOT happening now.

EXAMPLES:

• They can’t be travelling by bus. There is no bus service on Sundays.

can’t

We use can’t/couldn’t have + past participle or can’t have been + -ing to say that we are quite sure that something did NOT happen or was NOT true in the past.

EXAMPLES:

• You can’t/couldn’t have seen John last night. He was in hospital.
• She can’t/couldn’t have passed the test. She didn’t even open the books.

Note that for negative deduction we use can’t and NOT mustn’t He can’t be that famous. (NOT He mustn’t be that famous.)

could/might/may

We can use could/might/may + infinitive to say that it’s possible that something is true (but we are not sure).

EXAMPLES:

• I can’t get hold of him on the phone. He could/might/may be away.
• We didn’t do anything when we could and now it could/might/may be too late.

could/might/may

We use could/might/may be + –ing to say that we are quite it’s possible that something is happening now (but we are not sure).

EXAMPLES:

• Tom isn’t at the office. He might/may be working from home today.
• ‘Why isn’t she picking up her phone.’ ‘She might/may be driving.’

could

We can use could have + past participle to say that something was possible in the past but did not happen.

EXAMPLES:

• He could have played in the first division, but he had a terrible injury.
• He could have had better jobs if he had spoken English.

Note that we use might not or may not (NOT could not) to talk about a negative possibility.

• He seems too calm. He might/may not be aware of the risks.
• She might/may not have heard us. Knock again. too late.