1) What are modal verbs?
- Common modal verbs are 'Can', 'Could', 'May', 'Might', 'Will', 'Would', 'Shall', 'Should' and 'Must'. They are used to express ability, request, permission, advice, etc.
Examples:
I can swim. (Ability)
Could I have some tea, please? (Request)
You should send an email. (Advice)
- Modal verbs have the same form for all subjects and they are followed by the infinitive without 'to'.
Examples:
I can swim.
My brother can swim.
They can swim.
2) 'Must' and 'Mustn’t'
- We use 'must' to express obligation and certainty.
Examples:
They must answer six questions. (Obligation)
You haven’t eaten all day. You must be hungry. (Certainty)
- We also use 'must' to give strong advice.
Example:
You must see a doctor. (Strong advice)
- We use 'mustn’t' to talk about prohibition.
Example:
You mustn’t park here. (Prohibition)
3) Negative form of 'must'
The negative form of 'must' is 'must not' (mustn’t).
Example:
(+) She must see a doctor.
(-) She must not see a doctor.
4) Question form of 'must'
We make questions by putting the subject after 'must'.
Example:
(+) She must see a doctor.
(?) Must she see a doctor?