A modal verb talks about possibility, ability, permission, obligation, or condition. The main modal verbs are:
- ought to
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 base form.
- I should run to the shop.
(subject/I + modal/should + main verb in base form/run)
- I should not run to the shop.
(subject + modal + not + main verb in base form)
- Should I run to the shop?
(modal + subject + verb in base form)
- Should I not run to the shop?
(modal + subject + not + verb in base form)
- 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?