There are 13 Modals including the Semi Modals. Out of them shall, should, will, would, can, could, may, might, must, ought to and used to are always anomalous. Dare and need are anomalous when used as auxiliaries and not anomalous when they are used as principal verbs.
Auxiliary, or helping verbs, are used before infinitives to add a different meaning. The following auxiliaries are called Modal Auxiliaries or Modals.
|Modal Auxiliaries||Meanings / Functions|
|can||ability, permission, request, possibility|
|could||ability, formal request, possibility|
|shall||futurity, willingness, intention, suggestion, insistence|
|should||obligation, necessity, expectation, advisability|
|will||willingness, intention, prediction, insistence|
|would||willingness, habitual action in the past, probability, wish, desire|
|may||permission, possibility, wish, purpose, concession|
|might||permission, possibility, concession, reproach|
|must||necessity, prohibition, compulsion, obligation, deduction, certainty, probability|
|Quasis / Semi Modals||Meanings / Functions|
|ought to||moral obligation, probability, certainty, advice, necessity, duty, fitness|
|use to||discontinued habit|
|need||necessity, obligation (used in negative and questions)|
|dare||defiance, challenge, boldness (used in negatives and interrogatives)|
Use can and could to say that someone is able to do something or Can and could are also used for asking for information or help for offering something, and for suggesting something.
|Positive and Negative|
|I / we / you / they / he / she / it||can
|can||I / we / you / they / he / she / it||do?
Use may to ask if you are allowed to do something, or to give someone permission to do something.
|I / we / you / they / he / she / it||may (not)
Use must when you think it is necessary or very important to do something :
|I / we / you / they / he / she / it||must||do
For the past (yesterday / last week etc.), we use had to + infinitive (had to go / had to do / had to write etc.) :
I had to go to the bank yesterday. [= It was necessary for me to go the bank].
We had to walk home last night. There was no bus.
I mustn’t do it = it is important not do it. it is a bad thing to do:
I need not do it = it is not necessary to do it. I do not need to do it :
We can also say do not need to ... => need not.
(Someone) should do something = it is a good thing to do or the right thing to do :
|I / we / you / they / he / she / it||should
Use will when you are order or asking someone to do something.