1. They are followed by an infinitive without TO.
If you want to make an interrogative or
negative sentence, you don’t need other
auxiliar verbs, but the same modal verb.

2. CAN
1) ability in the present ( saber, poder)
2) Probability
Lucy can swim.
She can’t swim
Can Lucy swim? Yes, she can/ No, she
can’t

3. COULD
1) Ability in the past ( sabía, podía)
I could read when I was 2 years old
I couldn’t read …
Could you read…?, Yes, I could. No, I
couldn’t

4. SHOULD
1) Advice (debería)
You should study more
You shouldn’t text your friends in class
Should I go to the doctor? Yes, you should/
No, you shouldn’t

5. MUST
1) Obligation ( deber)
You must study harder.
In negative…PROHIBITION
You mustn’t smoke in here
* There’s no interrogative.

6. HAVE TO
1) Obligation (tener que)
You have to talk in English
You don’t have to talk in English
Do you have to talk in English? Yes,
you do/ No, you don’t