Unit 8.1

Can and Could: Modals of Ability

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A modal verb is a type of auxiliary (helping) verb that has no meaning on its own but it modifies the main verb, changes its meaning and gives more details about the action.

Could is the past form of the modal verb can. These are types of modal auxiliary verbs used to express the idea of ability or permission.


Can/could always have the same form, even for the third person singular. It is used as a modal verb and can be used in the three forms: affirmative, negative and interrogative.


Its structure, in the affirmative form, is:
Subject + could + verb + …

Subject could Verb
I/You could work
He/She/It could work
We/You/They could work


Its structure, in the negative form, is:
Subject + could + not + verb + …

Subject could + not Verb
I/You could not work
He/She/It could not work
We/You/They could not work

Short version of the negative form is: can’t/couldn’t.


Its structure, in the interrogative form, is:
Could + subject + verb + …?

Could Subject Verb Question
Could I/you work ?
Could he/she/it work ?
Could we/you/they work ?



  • can cook very well.
  • She could rent this flat. She has a good job.
  • We can hear you heartbeat.


  • I can’t cook anything. 
  • She couldn’t find her wedding ring. 
  • We couldn’t smell the smoke from the other side of the city. 


  • Can you play the piano?
  • Could you help me with my homework?
  • Can you believe he’s single?


Could is the past, less direct and more polite form of can and it has almost the same usage, but it can refer to the past. Also, it is used to express disapproval, and with the verbs of senses and mental processes. We can use could in present to be more polite. Could is used to express:

  • abilities;
  • disapproval;
  • polite offers;
  • polite requests;
  • possibilities;
  • with verbs of senses (smelltasteseeheartouch…) and mental processes (thinkbelieverememberunderstand…).


The modal verbs can and could express ability, offers, polite requests and possibility. Could is also used to express disapproval, senses and mental processes, and it is the past form of can.

We can use it in its different forms:

  • affirmative: we start with the subject followed by could and the verb;
  • negative: we start with the subject followed by could not and the verb;
  • interrogative: we start with could followed by the subject and the verb (the sentence ends with a question mark).

For example:
— Affirmative: “Moving could be stressful.“ / “Moving can be stressful.“ = Could is used to express that moving is sometimes stressful and can that it is stressful most of the time.
— Negative: “We couldn’t share a flat!“ / “We can’t share a flat!“ = Could is used to express refusal and can to express impossibility.
— Interrogative: “Could I use the microwave?“ / “Can I use the microwave?“ = Could is used to ask for something in a more polite way.

NOTE: We don’t use could to give or refuse permission.
—  “Could I leave early today?” – “Yes, you can”; “No, you can’t.“ / “Yes, you could“; “No, you couldn’t.

Let’s revise this content within the {Form} section. Take a look at the {Example} section that shows its use within a context.

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