Modals of certainty
Hi, today we are going to learn about modal verbs of certainty.
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Let's get started.
Let's just have a quick refresh on what is a modal verb.
There are 9 pure modal verbs: must, might, may, will and would,
can and could and shall and should. So what should you remember about all modals?
1. Modals do not change, ever. So, "He must be tired."
Not, "He musts be tired." This is the same for all pronouns , I must,
you must, and so on.
2. Modals are followed by the infinitive without to.
So, "It must be 7am, my alarm is ringing."
Not "It must to be 7am..."
3. Negative modals use NOT or the abbreviation N'T.
So, "He can't win, he hasn't trained at all."
Not, "He don't can win."
4. Modals have no past form. So, this links
back to point 1, modals don't change. The verbs following the modal show the tense.
So, "I must have had a bad dream," and not
"I musted have had a bad dream."
So, let's look in more detail at modals of certainty.
They are: Must
Can't Couldn't
These are used when you are nearly sure of something being either true or not true.
It is much more definite than modals of possibility.
So, it helps to visualise a line of certainty.
On the far left, we have something that's 100% sure. In this case, it's cold. the thermometer shows –10°.
Modals of certainty come pretty close to this fact. It must be cold, you are shivering.
Modals of possibility have far more doubt. It could be cold, it's October but it could
also be warm and sunny. It’s a possibility. Then moving onto the negative end of the scale.
Back to our autumn day. It might not be cold, it could be warm. Its a possibility.
You’re not sure. Then when you are very sure that something
is not true, you use it can't or couldn't.
So, in this case it can't be cold, or it couldn’t be cold because people are swimming
in the sea. This is almost certain. And then on the far right, we have something that is 100% certain.
of being NOT true. It's not cold outside. The thermometer shows the temperature +30°C.
So how do we use modals of certainty? In the present tense
We use must + inf without to when we are sure that something is true.
For example: It must be from Diana because she's in Japan.
When we are sure something is NOT true we use can't/ couldn't (not mustn't)
It can't be from Diane because that's not her handwriting.
Or it couldn’t be from Diane because thats not her handwriting.
Be careful when you are sure something is not true, it is not what you would logically think.
If you are sure it's true, you use must, so if you are sure it's not true you
say mustn't , right? No, this is only used for modals of prohibition.
You mustn't walk on the grass. ( It is against the rules)
Instead, when you are sure some thing is not true you use can't or couldn't.
So how about talking about the past. We use must + have + past participle when we
are sure something is true. For example: Rob went out without his coat,
he must have been very cold. ( we are sure this was the case, it is not just possible,
you have evidence, he had no coat) When we are sure something is not true in
the past. We use can't /couldn't have + past participle.
For example: He can't have been cold, because he took a warm coat.
We are sure he didn't get cold because he had the warm coat. Again this is more than
just possible, we know he took the warm coat. Or he couldn't have broken the window, he
was at school. Again we are sure of this because he was at school.
It wasn’t possible. So now its your turn.
Fill in the gaps. 1. Everyone in the class.......... ( work) very
hard because you have all passed your First Certificate.
must have worked ( we are sure this is the case because we have evidence, they all passed)
2. I don't know how old the teacher is, but he looks quite young, so he …... (be) more than 25.
can't be ( we have evidence, he looks young, so we are pretty sure that he is not older than 25. )
3. I think she..... (be) a really happy person
because she is always smiling and laughing.
must be ( you have evidence so you are sure this is true)
Congratulations, you now know how to use modals of certainty in English.
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Modals of certainty