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Auxiliary Verbs “Can/Could” and “May/Might/Must”


Used to express ability (to be able to do something):

  • I can make jewelry.
  • He can’t speak French.
  • Can you open this jar?

Used to ask for permission:

  • Can I use your bathroom?
  • Can I leave now?
  • Can I raise the volume?

Used to make requests or suggestions:

  • Can I have more napkins?
  • Can I have the bill?
  • You can take this spot if you like.
  • You can do whatever you want.

Could (past form of can)

Describes an ability that someone had in the past:

  • I could swim when I was young.
  • You could see the boat sinking.
  • They could tell he was nervous.

Often used in auxiliary functions to express permission politely:

  • Could I take this jacket with me?
  • You could borrow my umbrella.
  • Could you please let me pass you?
  • Could I get you more water?

Used to express possibility:

  • All of them could ride in the van.
  • You could always stay at our house.
  • Could it be true?
  • This plan could really work out.


Used to ask for formal permission:

  • May I come in?
  • May I say something now?
  • May I ask one question?

Used to suggest something that is possible:

  • She may agree with this plan.
  • They may not be happy about what happened.
  • It may shower tonight.

Might (past form of may)

Used to suggest a smaller possibility than may does (actually, might is more common than may in American English):

  • He might have finished it.
  • I might go see a doctor.
  • I might not come this time.
  • It might be right.
  • You might have lost it.
  • The store might have been closed today.


Used to express something formally required or necessary:

  • I must complete the project by this week.
  • The government must provide health care for everybody.
  • Everyone must save the natural resources of the earth.
  • The building must have a fire alarm.
  • You must answer my question right now.

Used to show that something is very likely:

  • He must be a genius.
  • You must be joking!
  • There must be an accident.
  • She must be very tired.

[Quiz 21.1]

Choose the right word for each blank.

1)She (can, could, may, might, must) have practiced a lot. Her performance was amazing.
2)I can’t find my watch anywhere. I (can, could, may, might, must) have lost it.
3)Professor, (can, could, may, might, must) I ask a question?
4) (can, could, may, might, must) you please lower your voice?
5)You (can, could, may, might, must) be kidding! How is that possible?
6)I (can, could, may, might, must) speak both English and Chinese fluently.

[21.1] 1) must
2) might
3) may
4) could
5) must
6) can