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Modal auxiliary verbs in English

Modal auxiliary verbs 

To begin with, auxiliary verbs are basically “helping verbs” and there are two categories in English: main auxiliaries and modal auxiliaries. So, modal auxiliaries are helping verbs that connect with normal verbs (non-auxiliary verbs) to express a meaning, ask a question or negate.

Also, modal auxiliaries are not used with the main auxiliaries; to be, to have and to do, and do not make sense on their own, therefore, they must be connected with a normal verb in order to provide functional meaning.

The main auxiliaries are to be, to have and to do – see main auxiliaries, while the modal auxiliaries are: can, could, may, might, will, shall, should, must, need to, dare to and ought to.

Why are modal auxiliaries used? 

In English, we use modal auxiliaries to express modality, that is, all things ranging from capacity, obligation, ability, permission, suggestions, and recommendations – all possible situations.

On the other hand, main auxiliaries, are used to express more fundamental functions such as the passive, perfect tenses, negation, emphasis etc., hence “main auxiliaries”.

Modal auxiliaries are followed by the bare infinitive

All modal auxiliaries, apart from need to, dare to and ought to take the bare infinitive and not the gerund or “to + infinitive”:

  • Can: She can ride a bike. 
  • Could: Could you let me know? 
  • May: They may take issue with this. 
  • Might: I might see him on Friday. 
  • Will: I will not do it. 
  • Shall: Shall I get dressed? 
  • Should: You should not be so loud. 
  • Must: They mustn’t act like this. 
  • Need to*: We need to buy a car. 
  • Dare to*: We dared to confront the bully. 
  • Ought to*: She ought not to teach them.

No inflections with modal auxiliary verbs

Important to note, modal auxiliaries, unlike main auxiliaries, have no inflexions, that is, they take the same form for all persons. A quick example, 

I willWe will
You willYou will
He/she/it will They will
  • Take note of the modal auxiliary verb “will”, which does not change its form and has zero inflexions, as can be seen from this chart.

Modal auxiliaries are followed by normal verbs

So, just like the main auxiliaries, modal auxiliaries must be followed by an ordinary verb (as a bare infinitive). 

  • I should take his advice. 
  • You won’t know it. 
  • They can leave now. 
  • You couldn’t see me.

In these cases, the normal verbs are take, know, leave and see, all of which are also bare infinitives, that is, they’re not the form of a gerund or “to + infinitive”.