Modals: Can and Could

CAN

-Used to say that something is possible or allowed

Example:
I can meet you later if you want.
I can go out this weekend as long as I finish my housework.

-Used to say that someone has the ability to do something

Example:
He can speak seven languages.
She can solve math problems in 30 seconds.

The negative form of CAN is CAN NOT (contraction: can’t).

Example:
I’m afraid I can’t go to the theater with you on Friday.

-You use CAN’T to say that you believe something is not possible

Example:
You’ve just had dinner. You can’t be hungry already.

COULD 

-Sometimes could is the past tense of CAN

We use could especially with:
Hear, smell, taste, feel, see, understand,remember

Example:
As soon as I got in my room, I could smell the burning air conditioner.

-Is also used to say that somebody had the general ability to do something

Example:
She could dance well when she was in her teens.

-Is also used to say someone had permission to do something

Example:
We could go out at night. My grandparents weren’t too strict with us.

The negative form of could is COULD NOT (contraction: COULDN’T).

-Used to talk about possible actions NOW or in the future (especially to give suggestions)

Example:
You could stay in my house when you go to Paris.

-Used for actions that are not realistic

Example:
I am so hungry, I could eat a cow.

-We also use could to say that something is possible now or in the future. (similar to might in meaning)

Example:
She could be waiting for you at the hotel.