Modal Verbs of Deduction – must, may, might, could, can’t

Exercises

Explanation

1. Present Modals of Deduction

These forms help us evaluate situations happening right now or situations we can observe at the moment of speaking.

Must – a high degree of certainty

We use must when we are almost completely sure that something is true based on logic or clear signs.

Form: must + verb

Examples:

She must be practicing for the concert; I can hear the piano from her room.
They must know about the change in schedule; everyone else was informed.

Can’t – strong belief that something is impossible

We use can’t to say that something is extremely unlikely or logically impossible.

Form: can’t + verb

Examples:

He can’t be at the office; his car is still in the driveway.
This can’t be the final version; it has too many mistakes.

May / Might / Could – possibility without certainty

These verbs show that something is possible, but we are not sure. They all express similar levels of uncertainty, though might is often seen as slightly less certain.

Form: may / might / could + verb

Examples:

She might be preparing dinner, so try calling later.
They could be in the meeting room.
It may be the wrong folder; check the name again.

2. Past Modals of Deduction

When we interpret events that have already happened, we use modal verbs with the structure:

must have / can’t have / might have / may have / could have + V3

These structures allow us to talk about the past with different degrees of confidence.

Must have – strong belief about a past event

We use must have when we are almost sure something happened.

Examples:

She must have finished her project; her desk is completely clean.
They must have decided early; everyone seems prepared.

Can’t have / couldn’t have – strong belief that something did NOT happen

We use these forms to show that a past event was impossible or highly unlikely.

Examples:

He can’t have left already; his jacket is still here.
She couldn’t have spoken to you yesterday; her phone was broken.

Might have / May have / Could have – possible past events

These forms show that something was possible but we are not certain.

Examples:

They might have misunderstood the instructions.
He may have forgotten to lock the door.
She could have taken the earlier train.

3. Continuous Forms of Deduction

We use continuous forms to talk about actions that were in progress at a particular moment in the present or past.

Present continuous deduction

Used for actions happening right now.

Examples:

She must be working on the report; she hasn’t answered her messages.
He can’t be cooking yet; the kitchen lights are off.
They might be practicing in the sports hall.

Past continuous deduction

Used for actions that were happening over a period of time in the past.

Examples:

She must have been reading when you called; she didn’t hear the phone.
They can’t have been studying; their books were still closed.
He might have been fixing the car when the storm started.

4. Why We Use Modals of Deduction

Modals of deduction are essential for clear and natural communication. They help us:

express different levels of certainty, rather than simply saying “I think…”
make logical conclusions based on the information available
speak politely and carefully, especially when we are not completely sure
describe situations more accurately in stories, conversations, and problem-solving
explain evidence or observations in a more precise way

They are extremely useful in everyday communication, academic writing, professional discussions, and any situation where we need to interpret information thoughtfully.