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Modal Auxiliaries

Modal auxiliaries are a small group of auxiliary verbs that indicate ability, possibility, permission, or obligation.

  • We might be able to fix the engine ourselves.
  • You should talk to a dentist about your sore tooth.
  • Can I park my car here?
  • If I had enough money, I would travel around the world.
  • He could easily afford his own apartment, but he prefers to live with his parents.

The following list contains some modal auxiliaries.


Modal auxiliaries do not change forms for number, person, or tense. They always precede any other verb forms in the sentence, including other auxiliaries like be, have, or do. When used in present tense, modals are followed by the base form of the verb.

  • Maybe they should have asked Yoko what she thinks.
  • We might order a pizza after practice.
  • You must consider every alternative.

To form the negative with a modal, place not immediately after the modal and before any other auxiliary verbs. To form a question, move the modal to the beginning of the sentence, before the subject.

  • Should they have asked Yoko what she thinks?
  • Maybe they should not have asked Yoko what she thinks.

The negative of can is one word, cannot.

  • cannot run as fast as Kendra.

We have already seen the modal auxiliary will, which is used to create future tense verb forms. It can also express a definite intent or decision on the speaker’s part.

  • Tomorrow, the president will deliver the State of the Union address.
  • will finish this project even if it kills me.

Can indicates an ability to do something. The past tense is could.

  • A penguin can survive freezing water because it is well insulated.
  • Navigating the rapids can be dangerous.
  • could not see the fireworks from where I stood.

May and might, often used interchangeably, indicate possibilities or uncertain events. May can also indicate permission to do something.

  • It may rain tomorrow.
  • We might have to reschedule our game.
  • You may keep that umbrella, if you want it.

Must indicates a necessity or obligation, or expresses certainty about an assumption.

  • You must get a license before you become a truck driver.
  • If she stayed home, she must be sick.

Should indicates something that is appropriate or advisable.

  • You should try to study more.
  • Americans should eat more fruits and vegetables.

Could and would sometimes function as the past tense forms of can and will. More often, they indicate hypothetical or wished-for situations. They are often used with if clauses or in combination with subjunctive verbs.

  • I wish I could afford a motorcycle.
  • would love to have one.
  • If I were rich, I would buy a dozen.

Some grammarians include ought to, need, dare, and used to as modals or semimodals. Used to expresses a habitual action in the past, one that is no longer being repeated. Used to can be used interchangeably with would in this sense, but because would also has other meanings, it requires an indication of past time to make sense.

  • We used to go to the beach every summer.
  • Or: When I was a child, we would go to the beach every summer.
  • He used to smoke three packs of cigarettes each day.
  • Or: Before he got sick, he would smoke three packs of cigarettes each day.

Have to, meaning to be required or forced to do something, can be used interchangeably with must, but have to is not considered a modal because it varies for tense and person.

  • She has to turn in the assignment by noon or she will fail the class.
  • Or: She must turn in the assignment by noon or she will fail the class.
  • They will have to demolish the old building before they start new construction.
  • Or: They must demolish the old building before they start new construction.

Must cannot indicate past tense. Use had to instead.

  • I locked myself out of my apartment, so I had to call the manager.
  • Not: I locked myself out of my apartment, so I must call the manager.

Gray Area: “Can” versus “May”

An often-repeated grammar rule says that can indicates an ability to do something, while may indicates what is allowed or permitted.

  • Can she run a mile in less than six minutes?
  • May I have another piece of cake?

In reality, this distinction in meaning is often difficult to make, so can and may are sometimes used interchangeably.

  • You may keep that umbrella, if you want it.
  • You can keep that umbrella, if you want it.
  • (Is the speaker granting you permission to keep the umbrella, or informing you that you have the ability to keep it?)

In general, may is preferable for polite requests or suggestions. Would, could, and might can also introduce polite requests: Could you carry this for me? Would you like another cup of coffee?

Gray Area: “Will” versus “Shall”

Formerly, shall was used as the first person form of will to express future tense. Using will in first person implied intent or definite decision. When shall was used in second or third person, it expressed obligation.

In modern American English, shall has generally been replaced by will. Shall is reserved mainly for contexts in which the speaker wants to sound formal or extremely polite.

However, when shall and will introduce questions, they have an important distinction in meaning. Shall asks for a preference or offers a polite suggestion, while will indicates future tense.

  • “Shall we get a cup of coffee?” means “Do you want to get a cup of coffee?”
  • “Will we get a cup of coffee?” involves speculation about future events, such as: “Do they serve coffee at this restaurant?” or “Is coffee included in the price of the meal?”

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