Chapter 5-2-1: Modal Auxiliary Verbs (Modal Auxiliaries)


Common auxiliaries are "can," "could," "may," "might," "must," "ought," "should," "will," and "would." A verb like these is called a modal auxiliary and expresses ability, certainty, necessity, obligation, possibility, or willingness. Placing a modal before a verb adds a different meaning to the verb. For instance, in the sentence “Sky can sing”, the word “can” indicates ability.

Almost all verbs in English are followed by either the infinitive or the gerund form of the verb.

Consider the following examples:

She wants to sing. (infinitive)

She enjoys singing. (gerund)

Modals are the exception to this rule. Modals are special verbs which are not followed by the infinitive or the gerund form of the verb. Modals are followed by the base form of the verb: She can sing. He could think. They may leave. She might quit. We will win. She shall improve. People would talk. You should remain silent. It must eat.


Affirmative Form

The modal comes first in the verb phrase (after the subject and before another verb):

  • I can leave now.

  • You must listen to me.

Modals are not used with other modals:

  • I can hear the noise.

  • I can would hear the noise.

Negative Form

The modal comes first in the verb phrase (after the subject and before another verb):

  • I wouldn't want to eat that.

Use the full form in formal contexts, or for emphasis:

  • I cannot hear the noise. I can not hear the noise.

  • I would not want to eat that.

People do not use "do not," "does not," or "did not."

  • He didn't could move the couch.

Interrogative Form

In the question form, the subject and the modal change position to form questions. People do not use "do," "does," or "did:"

  • Could you pass me the salt?

  • Shall I pour you another drink?

  • Must we leave so soon?

  • Need they be worried?

List of Modal Verbs

Verbs can be categorized into three groups to express modal meanings:

Core modal verbs: can, could, may, might, will, shall, would, should, must

Semi-modals: dare, ought to, used to, need

Other verbs that are not modals but can sometimes be used with modal meanings: have (got) to, need to, be going to and be able to

The highlighted word in each of the following sentences is a modal auxiliary:

Zora was pleased to learn that she could take several days off.

The small freckled girl told her neighbours that she would walk their dog for an appropriate fee.

Henry told Eliza that she ought to have the hole in the bucket fixed.

The principal told the assembled students that the school board might introduce a dress code next autumn.

According to the instructions, we must leave this goo in our hair for twenty minutes.

As a reminder, several words may intervene between auxiliaries and the verb which goes with these auxiliaries, as in the following sentences:

They have not delivered the documents on time.

The treasure chest was never discovered.

The health department has recently decided that all high school students should be immunised against meningitis.

Will you walk the dog tonight?

The ballet corps was rapidly and gracefully pirouetting about the stage.

Table: Function of English Modals [Quick Reference]

The following table provides a list of common English modals and their function. You may wish to bookmark this page.


Function + Modal & Tense

  • Can indicates if someone is able to do something or not in the present.

  • Could is employed to talk about past ability.

  • Negative forms: cannot (can’t), could not (couldn’t)


  • Can you program?

    • Yes, I can. I can program in many languages.

    • No, I can’t. I cannot program at all.

  • Could you stay out late when you were young?

    • Yes, I could. I could stay at a friend’s until 10.

    • No, I couldn’t. I could not stay out past 7.

  • I slept rather poorly—I could hear you two arguing all night.

Offers, Permission, and Polite Requests

Function + Modal & Tense

  • May, can and could are used with “I” and “we” in a question to ask permission.

  • Can, could and would are used with “you” in a question.

  • Refusing permission: could is not used to refuse permission.

  • Might can be used to request permission in formal settings; however, "may" or "may not" is used in reply to the question. "Might can also be used as a suggestion.

  • Negative forms: may not (Ø), cannot (can’t), could not (couldn’t), would not (wouldn’t). This form can be used as a reproach to request that someone stop doing something undesirable, or to do something they are not doing that we want them to do.

  • Casual versus formal: can is considered casual speech and should not be used in formal situations.

  • Notes:

    • can is considered casual speech and should not be used in formal situations;

    • the two words will you can be used for a limited number of phrases as a less polite or less formal method of using "would."


  • Hey buddy, can I get you a slice of pizza?

  • Sir, could I offer you some tea?

  • Ma’am, may I offer you some tea?

  • No thank you. May I have some water instead? No you mayn't.

  • Might I get you a crumpet? Yes, you might may.

  • You might want to try that with some raspberry jam.

  • Could I also gets some biscuits with that, please?

  • Mom, can we go out to a restaurant tonight?

  • Can you turn down the music Fred?

  • Can’t you turn down the music, Fred? Why can’t you be nice?

  • Could you have that delivered to me? Yes, I can. No, I can’t. Yes, I could No, I couldn't.

  • Could I not do everyone’s laundry for them?

  • Would you mind passing the butter please?

  • Would you please not shout so loud?

  • You can't park there.

  • Jack, will you get the door for me, please?

  • Sir, will would you like me to unpack your bags for you?

Necessity, Obligation, Obligation to Abstain, and No Obligation

Function + Modal & Tense

  • Must is used when something is compulsory or absolutely required.

  • Need can be used in a modal form when asking questions.

  • Need also has a rare use where it is paired with a negative word or phrase (e.g. no one, nobody, nothing).

  • Have to and had to when acting in a modal form.*

  • Need to, when acting in a modal form.*

  • Had to shows obligation in the past. It is the past form of "must."

  • Must not is used when there is an obligation NOT to do something (forbidden). That is to say, there is a requirement to abstain from something.

  • Do not have to and does not have to (don’t have to, doesn’t have to) is used when there is no obligation to do something. It means that it is your choice (voluntary).

  • Need not (needn't) is the same as "do not have to." It gives permission to someone not to do something.

  • Did not have to (didn’t have to) is used when referring to something in the past.

  • Future form: will have to and will need to are used more than "must" to express future obligations. "Must" is sometimes used to make general or personal references to the future.

* Note: “have to” and "need to" are not modal auxiliaries; however, they are included here because they act like modals (they act similar to “must”). They are the only words on the list requiring an “s” in the third-person singular form. People use “have to” when they want to talk about obligationsthings they have no choice about doing. However, they use “need to” when they want to talk about things that are necessary to do in order to achieve a certain goal or for something else to happen.


  • Mr. Spence, you must always arrive on-time for work.

  • Johnnie, you have to look both ways before you cross the street.*

  • Must she concentrate more on her studies?

  • She had to appear in court yesterday. She has to appear in court today.*

  • Need he continue? No one need know his identity.

  • He needs to continue if he wants to pass the course.*

  • The judge told Ellis that she had to complete her community service before last Saturday.

  • You must not drive on the right-hand side of the road in England.

  • Your doctor told you that you must not return to work.

  • You do not have to submit your taxes until March.

  • He does not have to join the army because he has a severe case of asthma.

  • You needn't concern yourself with the details. Just sign.

  • You needn't have given her the money. It was unnecessary. She doesn't need it.

  • I don’t have to eat spinach if I don’t want to.

  • You did not have to buy her such an expensive present!

  • She will have to file her taxes before April.*

  • They will need to work harder if they want to enter college.*

  • I must not forget to follow instructions next time.

Advice and Ideals

Function + Modal & Tense

  • Should and ought to are used for:

    • giving advice (it is a good idea to …);

    • expressing a moral obligation; or

    • expressing an idea situation.

  • Would can be used to offer advice less directly with verbs such as advise, imagine, recommend, say, suggest, and think.

  • Negative forms: should not (shouldn’t), ought not to (oughtn’t to)

  • Past forms: should have + the past participle or ought to have + the past participle

  • Note: "ought to" is less common and more formal than "should."


  • You should always begin preparations for an English essay several days before the due date.

  • They ought to pay attention when operating such heavy equipment.

  • We ought to have told him instead of keeping it a secret.

  • We ought to have told him instead of keeping it a secret.

  • I would recommend that we stay here until the rain passes.

  • You should not drive your vehicle when there’s a blizzard.

  • They ought not to have climbed the fence.

  • Should she be worried?

  • Ought she to be concerned?

  • We should have frozen the meat.

Conditional, Desire, and Past Habit

Function + Modal & Tense

  • Would can be used to express:

    • an action that is conditional upon something;

    • a desire to have or to do something;

    • something that was done habitually in the past; and

    • the future from a past perspective.

  • Negative form: would not (wouldn’t)

  • Notes:

    • use the words “would like to” express desire; and

    • people use used to to talk about states of being in the past instead of "would."


  • If I had a pen, I would take notes.

  • I would like to become a lawyer.

  • When I was young, I would swim all summer long.

  • When I was young, I thought that I would become a pilot.

  • If I had money, I would not be here right now.

  • I wouldn’t want to be in her shoes.

  • When I was young, I wouldn’t get up until 8 am.

  • When I was young, I used to live in New Brunswick.

Certainty, Probability, Possibility, Guessing, Habits, and Predicting

Function + Modal & Tense

  • Will (I'll, he'll, you'll, she'll, they'll, it'll) is used to express certainty, general truths, and habits.

    • Note: Will is also used to express the future.

  • Must can also be used to express probability. It is usually a deduction made by someone.

  • Must have expresses a deduction about something in the past. The past form is “must have + the past participle”.

  • Should and ought to express strong possibility.

  • Can, could and may express possibility.

  • Might also indicates possibility; however, it usually means less of a possibility than “could” or “may”. There is a weak possibility.

  • Cannot (can’t) means that something is not at all possible. It can be used as a negative form of "must."

  • Negative forms: will not (won’t), must not (mustn’t), could not (couldn’t), may not (Ø), might not (Ø)

  • Regret / disapproval / criticism: use could have + the past participle. People also admonish other people with the "How could you?" expression.

  • Notes:

    • "ought to" is less common and more formal than "should;"

    • A noun phrase + ’ll is normally unacceptable in writing; for example, it is incorrect to write that "Mother'll be late."


  • He will drown if he tries to swim across the Atlantic. He'll die.

  • The baby will get upset if you try to feed it lemon juice.

    • I will get up early tomorrow for work. (example of "will" in the future, not to be confused as a modal)

  • An hour has passed. She must be at home by now.

  • There must be a fire in here somewhere. I can smell smoke.

  • I saw that candy dish was empty yesterday. The children must have eaten all of the candy.

  • We should arrive tomorrow, unless the flight gets cancelled.

  • The opera ought to begin in five minutes.

  • We can go on vacation if we decide to because I've accumulated enough vacation days.

  • That electric motor may short-circuit if you don't dry it properly.

  • You should sterilize that and put a bandage on it. Otherwise, it could get infected in this dirty environment.

  • He could have slept over instead of driving home.

  • My aunt might visit today. I’m really not sure, though.

  • You can’t possibly be serious! I won’t eat that.

  • You mustn’t press the red button.

  • This cup must be yours. It can't be mine—my name is not on it.

  • I couldn't have reached that. I'm too short.

  • You could have warned me. I could have been hurt.

  • How could you have betrayed me this way?!

Using "should," "would," and "could" in the Past

To create the past tense of these three modals, add “have + the past participle” after the modal. For example:

    • “She should have eaten something before coming to class.” “You should have been there.”

    • They would have taken they money if they had the chance.

    • “You could have asked for a refund, you know. You would have received one.”

Using Modals as Questions

Since modals are auxiliaries, simply move the modal before the subject to create a question. For example:

    • He can read. → Can he read?

    • They would work long hours. → Would they work long hours?

Exception: remember that “have to” is actually not a modal (it is a regular verb) and therefore requires “do, does, or did” to make a question.

    • George has to wash his hands. → Does George have to wash his hands?

Modals and Reported Speech

Could is used in place of "can" when reporting what someone said in the past.

  • "Sir, since you are a VIP, you can consume alcohol anywhere." Your honour, he told me I could drink alcohol anywhere.

  • The attendant said, "You can go straight to the front of the line." She told me that I could come to the front of the line.

Would is used in place of "will" when reporting what someone said in the past.

  • "I'll be there tomorrow at 10 o'clock," said Debbie. Debbie said that she would be here today at 10 o'clock.

  • The analyst said "that Microsoft shares will drop." → The analyst said that Microsoft's shares would plummet.

Strange Modals

  • Had better can be used to make a strong recommendation, to suggest expedient behaviour, or to give instructions under threat.

    • “She had better bring an umbrella with her today or she will get wet.”

    • He had better pay the fine before the weekend.” / He'd better pay the fine before the weekend.”

    • You had better mow the lawn or you'll be grounded.” / “You'd better mow the lawn or you'll be grounded.”

    • Hadn't they better leave before your parents get home?

  • Shall is not frequently used in North America; however, it is used in Britain. It can be used to make offers, suggestions, or advice as well as to express predictions, intentions, and formal commands.

    • Shall can replace “could” when asking a question.

      • Shall I call you a cab?”

      • Shall I get the doorbell?”

    • Shall can also be used to replace “will” when discussing a future action.

      • “I shall do my best to do better in the future.”

      • “I shall try to visit her more often.”

    • Shall can be followed by have to, need to and be able to.

      • “I suppose that I shall have to admit that I did it.”

      • We shall have to find a carpet to hid the corpse in.”

    • Shall not or shan't are the negative form of "shall."

      • “I shan't be home for supper tonight.”

Degrees of Probability

The image below provides a rough idea of how probable an action is based on the modal used.

Degrees of Formality

Some modals are more formal than other ones when making offers or polite requests.


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Attribution information for this page: Written by Heather MacFadyen and Jamie Bridge with adaptations from / (some information in the table adapted from Pearson-Longman [ keywords: Modals, Modal Auxiliary Verbs, Modal AuxiliariesPageID: eslid03742