Certainty: How sure we are about something

Possibility: We are only making a guess, we can think of other possibilities.

DEFINITIONSDEFINITIONS

I think something is

possible at the present time

Do you know where John is?

Well, he must be in

the cafe…as usual

I’m not sure, he may be in

the toilet

No, no. He is in the

principal office…

I saw him!

Who really knows where he is?

Peter AndrésPeter Andrés Martha Martha* Martha! She saw him. She is

sure! She is saying a statement.* The other students are just

guessing

Where is John? Where is John?

He isis in the principal office.He must must be in the cafe He may/might/coulmay/might/couldd be in the toilet

100 % 100 % suresure

95% sure95% sure

Less than Less than 50% sure50% sure

Have you seen? Sara is so slim

Yeah! I see.

I would like to know what her

secret is ...

Perhaps she is sick... What do you think?

…Well ,she looks well. She can’t be

sick.

She mustn’t eat much fatty food

now.That’s why she has lost

weight

I have no idea but she may not have the same lifestyle she had before.

Oh! Shut up! You know

nothing! She is not sick at all. She got liposuction last month!

Who really knows about Sara’s beauty secret?

Betty Melissa Katie Sandy

*Sandy! She knows the truth* The other girls are just

thinking

Is Sara sick?She is not sick She She can’tcan’t be sick (I think it’s impossible)

She She must not must not eat much fatty food She She may not / might may not / might not not have the same have the same lifestylelifestyle

100 % 100 % suresure99% 99%

80% 80%

50%50%

To talk about certainty and possibility in the present, we use:

Must- May - Might- Could

Can’t/ couldn’t – Mustn't – May not – Might not

I think something is

possible in the future

Will Julio pass the test?

The test will be very difficult for everybody…He may pass the test but

who knows?

He’s been studying very

hard. He should pass the test

He’s very good student. He will

pass the test

His classmate his mother his teacher

Who thinks that Julio will pass the test?

*the teacher! She’s making a sure prediction

* The rest of them are speculating

Will Julio do well on the test?

He willwill do well on the test.He shouldshould /ought toought to do well on the test. (expectation)

He may/might/could may/might/could do well on the test.

100 100 % % 90%90%

50% 50%

To talk about certainty and possibility in the future, we use:

Will- Should- May. Might- Could

Won’t – Shouldn’t – May not – Might not- Could not

100 100 % %

suresure90% 90% suresure

-50% -50% suresure

He won’t won’t do well on the test.He shouldn ’tshouldn ’t/ought ought not to not to do well on the test. (expectation)He may not /might may not /might not /could not not /could not do well on the test.

Will Julio do well on the test?

To be a detective _____ be a very interesting job.

I don’t know much about the things a detective does, but I

think he ___ work solving mysteries and crimes.

What I am sure about is that a detective ____ know how to use a gun to protect himself

from the criminals. This job is really dangerous

Certainty or Possibility?must

may

must

Also a detective ______ coward.He ____________ fear the

unknown! And be very brave!Maybe this job is hard…He

_______ spend nights looking for clues.

I don’t know if I’m right or not but this job ______ be quite tiring

too.

can’tmust not

might

may

Mary has fallen asleep.

Yesterday, at the party…

She had been working all day at

home

She maymay have been have been tiredShe mightmight have been have been tiredShe couldcould have been have been tired

100 %100 %95% 95%

Less Less than than 50%50%

Therefore, by the end of the day…

She was was tired

SheShe must have been must have been tired

Read the exam carefully and choose

between option A or B

It seems that Bob is having problems to do the

exam…

He didn’t didn’t study. For

sure!

Yeah! He can’t have can’t have studied studied otherwise he could do the exam

Poor Bob. He mustn’t He mustn’t have hadhave had time to study

…or, he may not have may not have known known we had exam today

He didn’t didn’t studyHe couldn’t /can’t have couldn’t /can’t have studiedHe mustn’t have mustn’t have had time

He may not /might not have may not /might not have known about the exam

John is having problems to do the test because...

100 %100 %

95% 95%

90%90%

-50%-50%

1)A= Who was the man we saw with Anna yesterday?

B= I’m not sure. It ______________ been her brother but it’s just a guess.

2) A=I can’t find my umbrella. Have you seen it?

B= I don’t know. You _____________ left in the restaurant last night.

might have

may have

3) A=Why didn’t Dave answer the doorbell? I’m sure he was home that time. / B= He _______________ heard the ring. It’s the most probable.

4)Watch out for that dog. It_____________ bite you.

6) I bought this box of cereal yesterday. It ____________be empty already! It’s just impossible.

may / might

can’t

must not have

7)Sara knows a lot about movies. She ____________ go to the cinema very often.

8) The children ate all their food without complaining!

It ____________ been delicious!

must

must have