Rule 1. ‘Can' as a Modal is used to express power or ability to do something in the present. It is used in the sense of: be able to; be capable of; know how to.
Rule 2. ‘Can' as a Modal is used to express the possibility of some action in the present or future.
Rule 3. ‘Can' as a Modal is used to grant permission to do something in the present or future.
Rule 4. ‘Can' may be used when we seek permission.
Rule 5. ‘Can' as a Modal also indicates request in some contexts.
Rule 6. ‘Can' is also used to express bewilderment or, incredulity.
Rule 7. ‘Can' is also used to describe typical behavior or state.
Rule 8. ‘Could' as a Modal is used to express the past tense of ‘can'. ‘Can' in the Direct speech is turned into ‘Could' in the Indirect speech, provided the reporting verb is in the past tense.
Rule 9. ‘Could' as a Modal is used to express power or ability to do something in the past.
Rule 10. ‘Could' as a Modal is used to express the possibility of some action.
Rule 11. ‘Could' as a Modal is used to express permission to do something in the past.
Rule 12. ‘Could' as a Modal is used to make a polite request or seek permission in the form of a question.
Rule 13. ‘Could' also indicates result.
Rule 14. ‘Could' is also used to indicate suggestions.
Examples of Rule 1.
1.Birds can fly in the air.
2.Fish can swim in water.
3.He can drive a tractor.
Examples of Rule 2.
1.Even a mouse can help a lion.
2.You can pass this examination, if you work hard.
3.That can't be Mary-She's in hospital.
Examples of Rule 3.
1.You can come to me whenever you like.
2.She can go home, if she has finished her work.
3.She can go to bed now.
Examples of Rule 4.
1.Can I read your newspaper?
2.Can I take her home?
3.Can I eat some ice-cream, ma?
Examples of Rule 5.
1.Can you help me with this box?
2.Can you feed the cat?
Examples of Rule 6.
1.What can they be doing?
2.Can she be serious?
3.Where can she have put it?
Examples of 7.
1.He can be very tactless sometimes.
2.She can be very forgetful.
3.Shimla can be very cold.
Examples of Rule 8.
1.Direct Speech : Ram said to Sita, “Can you live in the forest?"
Indirect Speech : Ram asked Sita if she could live in the forest.
2.Direct Speech : The mother said, “ My son can never tell lie."
Indirect Speech : The mother said that her son could never tell a lie.
Examples of 9.
1.He could not walk because his foot was injured.
2.Surdas was blind, but he could write fine poetry.
3.Tagore could compose sweet tones of music.
Examples of 10.
1.You could easily pass this examination, If you decided to do it.
2.I could throw him out, but I did not.
3.He could be arrested on a charge of theft.
Examples of 11.
1.You could eat anything at the party.
2.You could take my scooter, if you needed it.
3.She could go to school in her own car.
Examples of 12.
1.I have finished my work. Could I go home now?
2.Could I use your phone?
3.Could I borrow your bicycle?
Examples of 13.
1.I am so unhappy I could weep.
2.What is for dinner? I could eat bread.
Examples of 14.
1.We could write a letter to the headmaster.
2.You could always try his home number.