The document discusses modals of deduction in English, which are used to express degrees of certainty about situations. It explains that must is used when something is considered very likely due to strong evidence, while might, may, and could indicate something is possible but not certain. Can't expresses certainty that something is not true. Examples are provided for each modal. The document also discusses using these modals to make deductions about past events, and provides practice questions for readers to fill in modals of deduction.

1. Coordinacion de lenguas extranjeras
Instituto Tecnológico de Tláhuac II
Teacher Eleazar Medina Garcés
*Information from English Aware and online information sources, rights to whom corresponds.
Modals of deduction
We use the Modals of deduction to say how sure we are about something
Modal of Deduction Must: We use must when we feel sure that something is true
because there’s very strong evidence.
1. He must be around here because his car is parked there
2. You are pilot, that must be interesting
3. You have worked all day, you must be tired
4. She’s not here. She must be in the kitchen.
Modals of Deduction Might and May: We use might, may or could to say that we
think something is possible but we’re not sure.
1. I heard a noise, there might be a cat on the roof.
2. He might be in his bedroom.
3. He may be in the Gym, sometimes he goes there.
4. Jerry is very tall so he might be good at basketball.
5. Don’t eat it! It could be poisoned!
6. Peter could be at the library.
Modal of Deduction Can’t: We use can’t when we feel sure something is not true.
1. He can’t be dead, I just talked to him on the phone
2. It can’t be a mechanical problem, the car is new
3. That can’t be James, James wears glasses
4. My wallet can’t be in my backpack, I already checked there
We form the modals of deduction like this:
+ Noun
Subject + Modal + Be + Adjective
+ -ING Verb

2. Coordinacion de lenguas extranjeras
Instituto Tecnológico de Tláhuac II
Teacher Eleazar Medina Garcés
*Information from English Aware and online information sources, rights to whom corresponds.
Practice Grammar
Modals of deduction must, might, can't
Instructions. Write the correct answer to fill the blanks.
must can't might
1. She isn't answering the phone. She be out.
2. They be Spanish, they're speaking Portuguese.
3. He have a job interview today - he's waiting to hear from
the company.
4. He drives an expensive car. He have a good job.
5. It's too early to have finished the exam. He have
finished.
6. Sara's very busy. She not be able to come tonight.

3. Coordinacion de lenguas extranjeras
Instituto Tecnológico de Tláhuac II
Teacher Eleazar Medina Garcés
*Information from English Aware and online information sources, rights to whom corresponds.
We use modals of deduction to make guesses about something that happened in the past.
The modals we choose show how certain we are that something happened or did not
happen, based on what we see and know.
Very probable must
Probable should
Possible
may
might
could
Possible (negative)
may not
might not
Very improbable (negative)
couldn't
can't
must not
• It must have been a terrible storm.
The speaker is almost certain that the damage was caused by a terrible storm.
• They should have started the repairs by now.
The speaker believes they have started the repairs.
• The city may have lost power.
The speaker is not certain if the city really did lose power. This is just one
possibility.
• That tree might have hurt someone.
The speaker is not certain if the tree really did hurt someone. This is just one
possibility.
• Dana's house could have been damaged.
The speaker is not certain if Dana's house really was damaged. This is just one
possibility.
Affirmative statements
Affirmative modals of deduction include must, should, may, might, and could.
These modals are followed by have + the past participle of the verb.
Subject Modal ‘have’ Past participle
I / We / You / They
He / She / It
must
should may
might
could
have started
PROBABLE
.

4. Coordinacion de lenguas extranjeras
Instituto Tecnológico de Tláhuac II
Teacher Eleazar Medina Garcés
*Information from English Aware and online information sources, rights to whom corresponds.
Negative statements
Negative modals of deduction include may not, might not, could not (couldn't),
cannot (can't), and must not.
American speakers use must not have to talk about past events that are very
improbable, but British speakers do not.
Subject Modal ‘have’ Past participle
I
We / You / They
He / She / It
may not
might not
couldn't
can't
must not
have done