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, could, may, might, will, would, shall, should, must, ought to, and used to. Words such as had better, need, 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.
- 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 (be, do, have): She can play the flute. / He is whistling.
Modal verb in question tag
Modal verb and contraction