How to Use Can or Could in a Sentence
Use of Can and Could
Can and could are modal verbs. They are used with other verbs to express ability, possibility, permission etc.
Where We Use ‘Can’
◇ Expressing Ability:
Can is used to express ability resulting from physical power or capacity or from knowledge.
Example: I can ride a horse.

He can speak three languages.
◇ Expressing Request:
Can is used to express polite form of request.
Example: Can you lend me your book for a day. Can you help me in solving the situation.
◇ Expressing Permission:
Can is used to ask for or give permission.
Example: Can I come in now?
Can I join with you?
◇ Can is used for present. We also use can for the future when we decide we are able to do something.
Example: We can go swimming tomorrow. You can come to see me tomorrow.
◇ We do not use Can with infinitive verb.
Example: We can play football today. Incorrect: We can to play football today.
◇ The negative form of Can is used as cannot (can’t).
Example: I am afraid that I cannot complete the task in time.
◇ Sometimes it is necessary to use (be) able to in place of Can.
Example: He is over sixty but he is still able to read without glasses. Now she is able to speak English fluently.
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Where We Use ‘Could’
Could is one of the modals. It is the past form of Can and is used to express possibility or ability
. ◇As past form of Can, Could is used to express ability.
Example: John said that he could get the tickets for us. At his top form, he could bowl at 100 miles per hour.
◇ Could is used to show what was possible in the past.
Example: He could cycle when he was four years old. He could buy any luxury car because he had plenty of money.
◇Could is used in polite form to ask something or ask someone to do something.
Example: Could you find a better place for me? Could I ask a question?
◇ We use could for present or in the future.
Example: It’s a nice day. We could go for a walk. When I shall go to London next week, I could stay with my uncle.
◇ We use could have to express past possibility.
Example: He could have done better if he had tried hard.
◇ We use (be) able to in place of could in the past form.
Example: He was able to finish the work before he left the office.
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