Modal Verbs

- They form the negative adding not to the modal verb.
- They form the interrogative without the auxiliary verb (They are their own auxiliary).
- They don't add -s/-es of third person.
- They are followed by infinitive without TO.

TYPES:

• ADVICE: Should, ought to, had better, be supposed to.

- For logic and advice or instructions: Should, ought to (they have the same meaning).
- To say the best option in a situation (stronger than the previous): Had better.
- To say the correct way of doing something: be supposed to.

• PERMISSION: Can, could, may, be allowed to.

- Asking for permission: can, could, may (very formal).
- Giving permission: can, may (not usually).          Note: couldn't is not used.
- About rules: Be allowed to.

• OBLIGATION: Must, have to, don't have to, needn't.

- Obligation by the person who speaks: must.
- When you oblige yourself: have to.               Note: both "must" and "have to" use HAD TO in past.
- Lack of obligation: don't have to, needn't.

• PROHIBITION: Mustn't.

• NECESSITY: Need to, didn't need to, didn't have to.

- Possitive form: Need to.
- Negative form: Didn't need to, didn't have to.

• ABILITY: Can, could, be able to.

- Present: Can.
- Past: Could.
- Other tenses: Be able to.

• POSSIBILITY/PROBABILITY: Must, may, might, could, can't, couldn't.

- 100% sure: must.        Note: past tense form is "must+have+Vparticiple" & "mustn't is not used.

- 50% sure, possible: may, might, could.     Note: past tense form is "modal+have+Vparticiple".

COULDN'T = IMPOSSIBLE                    MAY NOT/MIGHT NOT = POSSIBLE

- 100% impossible: can't, couldn't.     Note: past tense form is "can't/couldn't+have+Vparticiple".


Links to exercises:
Modal Verbs Advice
Modal Verbs Permission
Modal Verbs Ability
Modal Verbs Obligation
Modal Verbs Probability 1
Modal Verbs Probability 2
Modal Verbs Necessity
Modal Verbs Mix 1
Modal Verbs Mix 2
Modal Verbs Text Quiz
Modal Verbs Final Test