Can and Could are basically helping verbs. There are many similerties between can and could. So it is very difficult to differntiate can and could. We use first form of verb with can and could. Both are called modal verbs they show ‘a possibility’, ‘ability’ or ‘capacity’ in a sentence. ‘Can’ tells us something that is true or something which has strong sense of possibility. On the other hand ‘Could’ describes a weak possibility of something, or it refrers to something that might happen, but we are not sure weather it is true or not.
Correct use of CAN and COULD
Common Structures of CAN and COULD in a Sentence is given below.
POSITIVE SENTENCES (+): Subject + CAN or COULD + Verb (with first form of the verb)
NEGATIVE SENTENCES (-): Subject + CAN or COULD + NOT + Verb (with first form of the verb)
INTERROGATIVE SENTENCES (?): CAN or COULD+ Subject + Verb (with first form of the verb )
Note: we use first form of verb with can and could
Use of CAN and COULD
- To show Ability
CAN is used to describe that someone has the ability to do any task given to him. ( Ability which is present )
- . Alisa can speak five languages
- Simon can drive a bus.
COULD is used to describe that someone has the ability to do something in the past. ( use in past Ability )
- Clark could play hockey well when he was a kid.
- James could not ( couldn’t) get a job at that time.
- To show possibility
When we have to show that something is possible then we use CAN. It is used to show present possibility.
- Alcohol can cause fetal diseases. (cancer)
- Siam can stay with us when he come.
On the other hand when we have to describe something that is possible in past then we use COULD.
- A lot of crime could be prevented in the town.
- This new method could be an important step in invention.
- To get PERMISSION
When we want to get permission for something we use CAN. This is informal permission.
- Can my son use your pen? ( asking for permission )
- If Shusti want, she can go to the Hyde Park. ( giving permission )
COULD is used to get permission in formal way. This is the most polite way to ask for permission for something. “COULD” is more formal and polite as compared to “CAN”. (Asking for Polite Permission)
- Use for REQUEST
We use CAN when a question is asked but that question is not real. What is meant by not a real question? When we ask somebody to do something, its mean we want somebody to do our request. (In an informal way). For example request to friend or family member to fulfil your request. (It is Informal Request)
- Can you make me hot coffee?
- Can you hand me that white pen?
COULD is also used in a question as we use CAN. Question is not a real one because we ask somebody to fulfil our request in a polite way. When we use “COULD” its mean it is formal and polite request. (A Polite Request)
- Could you lend me this Arabic book?
- Could you tell me where the post office of Paris is, please?
- To make OFFER
When we offers some help to someone or want to do something for someone, we use CAN. (It is called Informal Offer)
- Can I help you to carry the luggage?
- If Seema likes, I can carry some bags for her.
On the other hand, COULD is used when we want to make a suggestion. (For Suggestion)
- If Nisha want we could go out for shopping after office?
- You could always call the police every day, if you are in danger.
- Use of CANNOT
Cannot is used in negative sentences. (When we are sure about something that is not true or something is surprising for us in a sentence)
- It can’t be raining today because the sun is shining and sky is clear.
(This sentence shows that someone is sure that it isn’t raining because the sun is shining and sky is clear.)
When something is not allowed, it is called negative saying.
- You can’t park the car in front of this bank.
- Use of COULD NOT
Could not is used in negative sentences. It is used when something is impossible or not true.
- Warner couldn’t have this house because of poverty.
(This sentences means that it’s not or it might not be possible for Warner to buy house even in future due to poverty.)
- Use of “COULD” as a conditional form of “CAN”;
When someone is talking about past times in form of conditional sentences, we use “could” in palace of “can”.
- If you called Tom, he could find you some suggestion.
- Naima could visit Wall of China if she had more money.
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