General characteristics

A

Modal verbs (can / could, may / might, must, shall / should / ought to, will / would) have the following characteristics:

• They are followed by the base form of another verb to indicate obligations, possibility, ability, permission, etc.
• -s is not added to the third person singular.
• They do not have infinitives or participles.
• They do not have proper past tenses (although could, would, should and might can sometimes be used as past forms of can, will, shall and may).
• Questions and negatives are formed without the auxiliary do.

B

Can is the modal verb used to express possibility and ability.

Can is the present form and could is the past and the conditional.

I can teach you, if you like.

She could read when she was only four.

This could be the beginning of a new story.

The full negative form is cannot, but this is used a lot less than the short form can’t.

We cannot / can’t go out tonight.

The full form is the past is could not.

They could not / couldn’t tell me anything.

C

Can we start writing now?

Could you wait a couple of minutes, please?

Can’t you pay a bit more attention?

Couldn’t you come with me?

D

‘Can you ride a horse?’ ‘Yes, I can. / No, I can’t.’

E

What can I do for you?

Where could we find a map?

How could you be so careless?