Could can be used in a number of ways:
As the past form of can.
I have another video about this, click here for my lesson about can, could and be able to.
We use could to say that an action or situation is possible in the present or future.
I could go shopping today.
I’m saying that it is possible. I’m not saying I will go – maybe I will, maybe I won’t, but I could – it’s possible.
We usually give more information so I would say:
If I get paid, I could go shopping today.
My friend could visit me next week.
It’s possible, but maybe he won’t – maybe he will have other plans, or choose not to.
3. We can also use could to talk about situations that are not realistic.
I’m so hungry, I could eat a horse.
(This is a common English expression, but of course I couldn’t really eat a horse).
I’m so tired, I could sleep for a week.
4. We can use could have to talk about possibility in the past.
My test went badly, but it could have been worse.
(It was bad, but it wasn’t a disaster)
I was lucky when I fell over, I could have been hurt.
(I’m talking about something in the past that was possible – but it did not happen – I wasn’t hurt, but I could have been.)
5. We can use could to say something would not be possible.
I couldn’t live in a busy city, I’d hate it.
(I’m saying that this unreal situation would not be possible for me. Luckily I don’t live in a busy city, I live in the countryside.)
6. In the past we use couldn’t have.
My holiday was amazing, it couldn’t have been better.
(My holiday was so amazing, nothing could have made it better – it was perfect.)
1. We use would to talk about imagined situations, situations that are not real.
I would like to be a millionaire.
(I like the idea of being a millionaire , I want to be a millionaire – but it is not real. I would like to be a millionaire.)
My friend wouldn’t want to be a doctor.
(It’s not real because he is not a doctor. I can imagine that this would not be a good job for him. He wouldn’t like all the blood.)
I’d help you, but I don’t have time.
(I am saying that if I did have the time, if I wasn’t busy, I would help you.)
2. We often use would in conditional sentences, and in unlikely situations.
If I had a million dollars, I would buy a Ferrari.
(In this case I don’t have a million dollars so it is an unreal situation, it is possible that one day I will have a million dollars, but it is unlikely.)
3. When talking about imagined situations in the past we use would have.
I would have called you, but I didn’t have your number.
(I didn’t have your number, so I didn’t call you)
4. We can use would to say that someone refused to do something.
I asked Chris to clean the kitchen, but he wouldn’t do it.
(He said no)
My car wouldn’t start this morning.
(My car refused to start, it wasn’t working properly)
5. We can use would to talk about things that happened regularly in the past.
When my sister and I were children, we would often play in the garden.
(Here it is similar to used to. We used to play in the garden.)
1. We use should to say that it is a good idea to do something, that something is the right thing to do.
You look sick, you should go to the doctor.
(It’s a good idea to the doctor)
The government should improve education.
(Improving education is the right thing to do.)
Should we go to the party, or should we stay at home?
(Is going to the party a good idea?)
2. We use shouldn’t to say that something is not a good thing to do.
You shouldn’t smoke.
(It’s bad for your health)
3. We often use should with ‘I think’ to show our opinion, or to ask for someone else’s opinion or advice.
You look tired, I think you should go to bed.
I don’t think you should go to the party.
Do you think I should wear this shirt?
4. We can also use should to say that something is not right, that we expect it to be different.
The price of this ticket is wrong, it should be £20, not £30.
(The ticket price says £30 but it’s wrong it should be £20)
The driver should be wearing his seatbelt.
(He is not wearing his seatbelt, this is dangerous, he should wear the seatbelt)
5. We can use should to say that we expect something to happen.
I’ve been studying a lot, I should pass the exam.
(I expect to pass the exam, I think I will pass the exam)
It shouldn’t be difficult to rent a car at the airport.
(I don’t think it will be difficult to rent a car when we get to the airport)
6. We use should have to talk about regret about something that we didn’t do.
Sorry I’m late. There was so much traffic, I should have taken the train.
(I would have been on time if I had taken the train, but unfortunately I drove my car so now I’m late. I regret not taking the train.)
7. We use shouldn’t have to talk about something that we did do, but now we regret it, it was the wrong thing to do.
I feel terrible, I shouldn’t have drunk so much last night.
(I drunk too much beer and now I have a terrible hangover.)
Compare these two:
There is lot of traffic, you should take the train.
There was a lot of traffic, I should have taken the train.
You can see with the first, I am giving my opinion or advice about what is a good idea to do.
And with the second I am giving my opinion about the past, what you should have done differently.
8. We can use ‘ought to’ instead of should. This is more formal.
You ought to go to the doctor.
You ought not go to the party.
Do you think I ought to go to the doctor?