The form of modal auxiliaries

The verbs listed below are Called “modal auxiliaries.” They are helping verbs that express a wide range of meanings (ability, permission, possibility, necessity etc.). Most of the modals have more than one meaning.
Auxiliary + the simple form of a verb
Can (a) Olga can speak English
Could (b) He couldn’t come to class
May (c) It may rain tomorrow
Might (d) It might rain tomorrow
Should (e) Mary should study harder
Had better (f) I had better study tonight
Must (g) Joe must see a doctor today
Will (h) I will be in class tomorrow
Would (i) Would you please close the door?
Can, could, may, might, should, had better, must, will, and would are immediately followed by the simple form of a verb.
- They are not followed by to. Incorrect: Olga can to speak English
- The main verb does not have a final –s. Incorrect: Olga can speaks English
- The main verb is not in past form. Incorrect: Olga can spoke English
- The main verb is not its –ing form. Incorrect: Olga can speaking English
Auxiliary + to + the simple form of a verb
Have to (j) I have to study tonight
Have got to (k) I have got to study tonight
Ought to (l) Kate ought to study harder
To + the simple form is used with these auxiliaries have to, have got to, and ought to.

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