Grammar

Modal verbs can and could

1,590 fill-in-the-gap exercises across 3 forms

Ability, permission, possibility and requests. Modal verbs take no -s, no to and no do.

Pick a form to practice

How modal verbs behave

Can and could belong to a small group that plays by its own rules. Three things are true of all of them:

• no -s for he, she, it — she can, never she cans
• no to after them — can go, never can to go
• no do in negatives and questions — can’t go and Can you go?, never don’t can

Learning those three points once covers can, could, may, might, must, shall, should, will, would.

What can means

• ability: He can speak Portuguese.
• permission: You can park here after six.
• a request: Can you pass the salt?
• general possibility: It can get very cold in February.

What could means

Three quite different jobs, and the context separates them:

• past ability: At five she could already read.
• a polite request or offer: Could you hold this? — softer than can
• present or future possibility: We could take the early train. — one option among several

The second and third have nothing to do with the past. Could is the polite and the tentative form as much as it is the past form.

could for a single past action

Here is the trap. For a general past ability, could is right:

She could play the violin at six.

But for one particular thing that someone managed to do on one occasion, English switches to was able to or managed to:

After three attempts he was able to open the door. — not he could open the door.

The negative does not follow this rule: couldn’t works for both. He couldn’t open the door is fine.

can’t for certainty

In the negative, can’t often means “that is impossible”, not “unable”:

That can’t be right. She can’t have left already.

Its positive counterpart is must: That must be right.

All forms

Mistakes to avoid