English modal verbs can could

Modal verbs can could

In English grammar, the modal verbs (can, could, may, might, must, will, would, shall, should, ought to, need) are auxiliary verbs used to describe ability, possibility or necessity.

Use an English modal verb + infinitive form of the verb without to. Do not change their form:
      She could speak German and Spanish.(NOT She could to speak...)
      Could you speak German before you went to live in Germany? (NOT Did you could speak German...)

1. Ability

Use the following English modal verbs to express ability:

Present tense: can, can’t, be able to, manage to
      I can’t drive.
      I manage to concentrate, but it’s difficult sometimes.
      I’m able to speak three languages.

Past tense: could, couldn’t, be able to, manage to
      They weren’t able to find the address of the shop.

Perfect tenses: be able to, manage to
      Have you managed to complete the assignment yet?

Future tense: be able to, manage to
      He won’t be able to come to the meeting this afternoon.

Use can/could to describe general ability in the present and past. This is more common than using be able to:
      Can she remember anything about incident? = (Is she able to remember?)
      She could speak German and Spanish but she couldn’t remember what happened when she was attacked.

To express ability related to one specific occasion in the past use couldn’t, was able to, wasn’t able to, but NOT could
      The police were able to determine that she could speak German and Spanish. (not The police could determine that she...)
      She couldn’t remember what had happened.

Sometimes, we use manage to to demonstrate that something was hard/difficult to do/achieve:
      I’ve finally managed to work out what the problem is!

For perfect or future forms, use be able to or manage to:
      Apparently the police have been able to identify her.
      The police have managed to locate her family and inform them of the attack.
      Soon she’ll probably be able to remember more about the incident. (NOT Soon she can probably remember more...)

2. Other ways to use can

Use can as an alternative to mean sometimes:
      People can do strange things when they’ve experienced such a shock. (= people sometimes do strange things/ have strange behaviour.)

Use can for asking and giving permission:
      Can I borrow your laptop this morning?
      Yes, you can borrow it, but I need it back this afternoon.

3. Possibility
Use must, might, could, couldn’t and can’t when there exists evidence, information or you believe that something is probably or possibly true (or untrue). Choose the appropriate English modal verb depending on the strength of the evidence which supports the ideas.
      Highly unlikely: can’t, couldn’t
      Highly likely: must
      Possible: might, may, could, may not, might not

Could, may and might communicate the same degree of possibility:
      She may/might/could remember some details about the incident.

Couldn’t and can’t express the same degree of probability. Normally they are used to talk about the past:
      The authorities realised she couldn’t be American. (= it was very unlikely that she was American)

May not and might not do are not the same as couldn’t when expressing probability:
      The shopping mall may/might not be open tomorrow because of the public holiday. (NOT the shopping mall couldn’t be open...)

Use may/may not, might/might not, could/couldn’t, must, can’t+infinitive+without to to describe present possibility:
      She may remember some details about what happened already. (= it is possible she remembers some details about the incident now)
      It can’t be very easy talking with someone who doesn’t remember anything about the past. (= it is very unlikely that it is easy)

We use may/may not, might/might not, could/couldn’t, must, can’t+be+-ing to describe events (possibly) taking place or in progress when the person is speaking:
      Her family must be experiencing some difficulty adjusting to the situation.
      The phone is busy. She might be talking to her family.

We use may/may not, might/might not, could/could not, must, can’t+have+past participle to describe past possibility:
      During the attack she must have struck her head. (= there exists strong evidence that her head was struck)
      She could have been alone. (a possible situation)
      She can’t have been from around here. (= there exists strong evidence she was a visitor to the area)

Use may/may not, could/could not, must, can’t+have been+-ing to describe possible actions happening in the past:
      She might have been trying to find something.
      She may have been running away from someone.
      She could have been waiting to meet someone.

Use may/ may not, might/ might not, and could/ could not+infinitive without to to talk about future possibility or uncertainty:
      She could make a complete recovery soon.
      The doctor may release her from hospital this afternoon.
      Her family might take some time to come to terms with what happened.

We can use may/may not, might/might not, and could/could not, must, can’t+be+-ing to describe possible actions in the future:
      I might be going to the movies later tonight.
      She may move back in with her family after this ordeal.
      She might not want to live alone anymore.

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