13. Modal Verbs

Modal Verbs are type of verbs that are used with the main verb to express possibility, necessity, ability, permission, expectation & obligation.

Examples:

1. May I sit here? (permission)
2. You must finish your homework today. (obligation)
3. He can swim. (ability)
4. They should arrive by noon. (expectation)

Features:

1. They are a type of auxiliary verb or helping verb.
2. Thus, all modal verbs are auxiliary verbs by all auxiliary verbs are not modal verbs.
3. They always come before the main verb. 
4. They cannot be there on their own in a sentence.
5. Modal verbs do not change by change in the (first / second / third) person. 
6. Modal verbs do not change by change in number of person (singular / plural).
7. Modal verbs have no 'ing' or 'ed' form.
8. Negative sentences are formed by adding 'not' to the modal verbs.
9. Main Verb after the modal verb is always used in its root form & past or present participle form of the verb is never used.

Examples:

1. I may visit my grandmother today. 

Here, 'may' is the modal verb and 'visit' is the main verb. The sentence will make no sense without the main verb 'visit'.

2. I can write very fast. (first person)

    You can write very fast. (second person).

    They can write very fast. (third person & plural)

Here, the modal verb 'can' doesn't change form with person or number.

3. Tom cannot (or can't) go to the party tonight. (negative form)