A Modal verb, also known as an auxiliary verb, is a kind of special verb which behave very differently and irregularly from normal verbs. Modal verbs are used, to describe what the speaker thinks about a particular situation, whether it is possible or not possible and so on. The modal verbs ‘can, will, shall, ought to, must, need may’ are used with the present tense while could, would, should, might are modal verbs used in the past tense.
The auxiliary verbs-be, do and have can serve as an ordinary verb in a sentence and as such cannot be called modals unlike the other auxiliary verbs. Most modal verbs function as a helping word as they cannot stand alone in a sentence like a main verb. Some expressions such as have to, had better, have got to, etc are not modal verbs but they are closely associated with modals and are often used interchangeably.
The modal verbs ‘can, could, may, might’ can be used in various situations to indicate-
You may watch T.V. after doing your homework.
I can not go to the party tomorrow.
May I come with you to the stores?
The modal verbs will, and shall are used to predict or state that an event will occur maybe in the future. Examples,
The modal verb ‘would’ has a variety of uses to indicate invitation, conditional, permission, request, question, habit, suggestion. Would is used in the contracted form as ‘d’. The negation is formed by adding not as in would not or wouldn’t.
The third person of a modal verb does not take a “-s” as is the practice in normal verbs.
Modal verbs are made negative by adding the word “not” even in the simple present and past tenses.
It would be incorrect to use certain modal verbs in the past or future tenses, for example modal verbs such as can and must retain their form irrespective of the tense.