A modal verb talks about possibility, ability, permission, obligation, or condition. The main modal verbs are:
- can
- could
- may
- might
- must
- ought to
- shall
- should
- will
- would
The form of a modal verb never changes, and they can only be used with a main verb. The main verb is always in the bare infinitive.
Positive
- I should run to the shop.
(subject/I + modal/should + main verb in bare infinitive/run)
Negative
- I should not run to the shop.
(subject + modal + not + main verb in bare infinitive)
Question
- Should I run to the shop?
(modal + subject + verb in bare infinitive)
Negative question
- Should I not run to the shop?
(modal + subject + not + verb in bare infinitive)
As in these examples:
- John can speak German.
- You mustn’t swim in that river.
- Could you pass me the salt please?
- Why couldn’t you open the box?
