How to use could and couldn’t in English sentences
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Could is the preterite of can. It expresses a capacity in the past. Couldn’t express a disability in the past, or something hypothetical.
Could can express a capacity or permission in the past (it is used as the past of can):
- I could smell something burning.
- My grandmother could speak six languages.
- I was totally free. I could go where I wanted.
Compare the following sentences:
- I can see something. (present)
- I could see something. (past)
Could could mean a hypothetical ability, i.e. something could be realized or be true now or in the future (it’s similar to might or may):
- You could succeed if you worked harder.
- I could go out with you but I’m tired.
- They could arrive anytime now.
- Could you do this exercise in one minute?
- If we had some eggs I could make you some pancakes.
We can use could to make a suggestion or talk about possible actions (we can then replace it with can):
- We could go to the movies tonight if you want.
- When you go to London next week, you could stay at Paul’s place.
- He could try to fix the car himself.
Could also express a logical deduction:
- It could be true.
- She could still be in bed.
- It could freeze tonight.
- Where’s Paul? He could be at Tony’s place.
Could have + past participle is used to express a possibility in the past, but that has not happened (to make a criticism, or to express a hypothesis, for example):
- You could have broken your arm.
- He could have tried once more.
- Your brother could have helped you.
- We were lucky: we could have run out of petrol.
Could also express unrealistic things:
- This place is amazing. I could stay here for ever.
Could allows you to ask for permission or something politely, in the present:
- Could I please use your bathroom?
- Could we move on to the next topic now please?
- Could you pass me the salt please?
- I’m busy right now. Could you call back later?
Couldn’t allows to express a disability in the past:
- I was so tired I couldn’t get up.
- I couldn’t start my car this morning.
This incapacity could be due to something that was not permitted or authorized:
- In high school, we couldn’t use our smartphones.
- Tina couldn’t go to the party because his parents wouldn’t let her.
With couldn’t, we doubt that anything is true, we are almost sure of what we are saying:
- It couldn’t be true.
- Paul couldn’t be at Tony’s place.
- You couldn’t be hungry. You’ve just had some pizza.
To express the impossibility of the past, we use couldn’t have + past participle:
- We had a really good evening. It couldn’t have been better.
- Tina couldn’t have gone to the party because she was sick.