Can and Could
What is modal?
A modal is a type of auxiliary (helping) verb that is used to express: ability, possibility, permission or obligation.
Can, can’t, could and couldn’t are using an ability or lack of ability. We call them modals of ability.
How to use can and can’t?
We use can and can’t for ability to do something and at a given time in the present or the future.
We use it for general abilities and skills. Can’t is the negative form of can and cannot in written English.
She can write well.
He can speak Spanish.
Jon can’t dance.
Joe can’t cook.
My nephew is only four years old, so he can’t play cards.
She understands the actions but can’t understand the language.
How to use could and couldn’t?
We use could to talk about a skill or ability in the past.
We use couldn’t for both speaking in general and when speaking about one particular occasion.
Couldn’t is the negative form of could and could not in written English.
I could dance tirelessly when I was ten.
What could you do when you were a kid?
I couldn’t reach the top drawer.
Note that we also use can and could with our senses: see, hear, smell, feel and taste.
I can hear someone is screaming.
The fabric looks so nice, you could touch it if you want.
More usage of can, can’t, could and couldn’t.
Possibility or impossibility
It can grow until it reaches the roof!
She can’t be serious.
It could rain today. (It is possible but not certain).
She couldn’t ride a bike when she was a baby.
Permission or prohibition
Can you lend me some money?
Could you lend me some money? (Polite or formal).
At that age? She can’t sleep late yet . (Refuse permission).
Could I get some? Yes, you can. (Do not use, Yes, you could or No, you couldn’t. When refusing permission use can’t)
I can drive you till the last block.
I could make you a great coffee!
These are the uses of can, can’t, could and couldn’t. Try what you learned with a friend. Enjoy!