The modal verb “CAN” has two tense
forms:
CAN –
Present
COULD –
Past
The construction “To
Be Able To Do Smth” is an equivalent and it is used to denote
some circumstances. For example:
She is not able to sing today. She has
a sore throat
He will be able to get tickets if we
ask him.
He was not able to come because he had
some troubles
The modal verb “CAN” is used in
it’s three meanings.
| Concrete |
Imperative |
Suppositional |
- Physical or mental ability.
She can speak English fluently |
You can go now
|
- Strong doubt about the present
Can you know it?
Could you know it? |
- To express circumstantial
ability/ the ability is presented by some circumstances.
You can get books at any
library.
You can buy this dress at any
shop |
Can I go there?
Could I go there?
|
- Strong doubt about the past
Could you have done it? I
don't believe.
|
| |
- Prohibition/forbidden by laws
or rules/.
You can't speak with your
mouth full.
You can't cross the street
here! |
- Doubt about the present and
the past
He can't be so silly.
She couldn't have done so. |
If there
are two negations in the sentence we should use "FAIL".
For example:
Could he have
failed to return?
She could not
have failed to notice it
