Modals (also known as modal verbs, modal auxiliary verbs, modal auxiliaries) are special verbs that behave irregularly in English. They usually give additional information about the function of the main verbs that follow.

Some characteristics of modal verbs:

  • They never change their form. You can't add "s", "ed", "ing"... 
  • They are always followed by an infinitive without "to" (i.e. the bare infinitive.) 
  • They are used to indicate modality and allow speakers to express certainty, possibility, willingness, obligation, necessity, ability


I can speak German.

She can speak German. (the verb speak must not be added with ‘-s’ because of the modal verb, can)

He might come to the meeting. (the verb come must not be added with ‘-s’ because of the modal verb, might)


List of modal verbs

Can, could, may, might, will, would, shall, should, must, dare, ought to, had better, need not

The Use of Modal Verbs

To express functions like:

  1. Permission
  2. Ability
  3. Obligation
  4. Prohibition
  5. Lack of necessity
  6. Advice
  7. Possibility
  8. Probability
Modal Verb Expressing Examples
must Strong obligation You must stop when the traffic lights turn red. 
Logical conclusion / Certainty  He must be very tired. He's been working all day long. 
must not Prohibition You must not smoke in the hospital.
can Ability can swim.
Permission Can I use your phone, please?
Possibility Smoking can cause cancer.
could Ability in the past  When I was younger I could run fast. 
Polite permission  Excuse me, could I just say something?
Possibility It could rain tomorrow!
may Permission May I use your phone, please?
Possibility, probability It may rain tomorrow! 
might Polite permission Might I suggest an idea?
Possibility, probability I might go on holiday to Australia next year.
need not  Lack of necessity/absence of obligation  I need not buy tomatoes. There are plenty of tomatoes in the fridge. 
should/ought to 50 % obligation  I should / ought to see a doctor. I have a terrible headache. 
Advice You should / ought to revise your lessons.
Logical conclusion He should / ought to be very tired. He's been working all day long. 
had better Advice You'd better revise your lessons 
Modals in the present and past
  Modals in the Present Modals in the Past
Obligation You must / have to stop when the traffic lights are red.  You had to stop.
Advice  You should see a doctor.  You should have seen a doctor 
Prohibition You mustn't smoke here.  You mustn't have smoked there. 
Ability can run fast. could run fast. now I am old. 
Certainty He has a Rolls Royce. He must be very rich.
He can't be American. His English is terrible. 
He must have been rich. He had a big house and an expensive car.
He can't have written that poem. He was illiterate. 
Permission Can I go out?  She could drive her father's car when she was only 15. 
Possibility It may / can / could / might rain. It's cloudy.  I guess it may / can / could / might have been Lacy on the phone.
Lack of Necessity You don't have to / needn't buy any tomatoes. There are plenty in the fridge.  You didn't have to / didn't need to buy tomatoes. 

 Must and Have To


Difference between must and have to


1. We use must to make a logical deduction based on evidence. It indicates that the speaker is certain about something:


  • It has rained all day, it must be very cold outside.
  • The weather is fantastic in Sao Paolo . It must be a lot fun to live there. 

2. Must is also used to express a strong obligation.


  • Students must arrive in the examination hall on time.
  • You must stop when the traffic lights are red.
  • must go to bed before 12 a.m.

Have to

Like musthave to is used to express strong obligation, but when we use have to there is usually a sense of external obligation. Some external circumstance makes the obligation necessary. 


  • have to send an urgent email.
  • have to take this book back to the library.

 Shall and Will


'Shall' and ' will' have the same meaning and are used to refer to the simple future. Note that 'shall' is not used often in modern English especially in American English.

The use of ‘shall’ and ‘will’

  • Will is used with all persons

Example: I/you/she/he/it/we/they will go there.

  • Shall is used with the first person singular and plural

Example: I/we shall go

  • The short form of will and shall is ‘ll.


I/you/she/he/it/we will/’ll call you.

I/we shall/’ll call you.

  • In the negative, the short forms of will not and shall not are won’t and shan’t respectively.


I/you/she/he/it/we/they won’t give up.

I/we shan’t give up.


The use of shall

It should be noted that shall is often used to make suggestions, offers or ask for advice. It is used in questions as follow:

  • Shall we stay or go out? 
  • Shall we dance? 
  • Shall I get his phone number if I meet him?
  • What shall I do to get rid of the pests on my plants?

As said above shall is used with first person singular and plural (I and we.) But there is a very special use of shall with other persons to make a promise, command or threat as noted below:

  • You shall not get in! (Command)
  • You shall pay for it. (Threat)
  • You shall get your money back soon. (Promise)

In American English shall is mainly used in formal or legal documents:

  • You shall abide by the law.
  • There shall be no trespassing on this property.
  • Students shall not enter this room.