The following are modal verbs:

Whether modals, modal verbs, modal auxiliaries or modal auxiliary verbs, they are all the same. The modal verbs and the primary verbs (be, do and have) are called auxiliary verbs. The difference between these two groups of verbs is that we can use modal verbs as auxiliary verbs only. In other words, we cannot use modal verbs on their own in a sentence, as they are not complete by themselves. We have to use them with other verbs, which must be in the simple present tense.

There are 11 moral verbs: can, couldmaymightwillwouldshallshouldmustought to, and used to. Words such as had betterneed, and dare are sometimes included as moral verbs. Each of them is used with another word to express ideas such as ability, intention, necessity, obligation, permission, possibility, wish, etc. that are not expressed by the main verb. Each one of them can express more than one of these ideas.

Modal verbs have one only form
Modal verbs remain unchanged when used in a sentence such as the following:
  • When used with singular or plural subject or noun, the modal verbs do not change their forms: She will arrive later. / They will arrive later.
  • Modal verbs have no –s form such as the third person singular. Not: She wills talk to us later. / Not: He shoulds get some rest.
  • Modal verbs do not have –ing participle form (Not: might + ing) or past participle form (Not: must + ed). 
  • Modal verbs cannot be used with another modal verb. Not: We can must get it done today.
  • Modal verbs cannot be used on their own in a sentence. They must be followed by other verbs. No: The repair would one hour. / Yes: The repair would take one hour.
  • Modal verbs can however be used on their own when the main verb is understood: He could be telling lies. Yes, he could. / She may be angry. Yes, she may.
  • When a modal verb is part of a verb phrase in a sentence, it comes first after the subject and is followed by a main verb in the base form (Subject + modal + basic verb + ... ):  or an auxiliary verb (bedohave): She can play the flute. / He is whistling.
 
Modal verbs have no infinitive form
Modal verbs are followed by the infinitive of another verb without to. There are exceptions: ought to and used to. These two are sometimes treated as modal verbs, and they are followed by simple verb.

 

Examples:

  • No: He can to drive a tractor.
  • Yes: He can drive a tractor.
  • You ought to be able to read the road sign from here.
  • We used to cross that river by ferry.

 

Modal verb in question
Modal verbs always come before the other verbs, but to form a question, the moral verbs are placed before the subject. 

 

Examples:

  • Will everyone join with me in singing the national anthem?
  • Must you always drink coffee to keep you awake?

 

Modal verb in question tag
Modal verbs are used in question tags.

 

Examples:

  • You would like some ice cream, wouldn’t you?
  • It shouldn’t be kept as a pet, should it?

 

Modal verb and contraction
In a negative statement/sentence, the negative word (not) or its contraction (n’t) comes after the moral verb. For example, the negative form of should is should not or shouldn’t. The only moral verb that does not have contraction is may.
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Examples:

  • You cannot (can’t) simply do what you like around here. There are rules to follow.
  • You may not see her. Her father doesn’t allow it. / Not: You mayn’t see her.

 

Modal verb and emphasis
When emphasis is intended, the moral verb is used in full. 

 

Examples:

  • We shall not let them do this to us.
  • Not: We shan’t let them do this to us.

 

Modal verb and wh-question
Wh-questions begin with what, when, where, who, whom, which, whose, why and how. All these wh-question words can be placed before the modal verbs to form wh-questions.

 

Examples:

  • This morning, my grandmother appeared more cheerful than my grandfather.
  • What can you do to help us?
  • When may I have my money back?
  • Where should we start looking for the missing puppy?
  • Who could pass me the salt?
  • Whom might I ask you want to speak to?
  • Which will growl if we get too close to it?
  • Whose would you say this is?
  • Why must you be so stubborn?
  • How shall we address the Queen?