Can you be quiet!

can: Permission

We sometimes use can to ask or give permission for something:

1. Can I smoke in this room?

2. You can't smoke here, but you can smoke in the garden.

(Note that we also use could, may, might for permission. The use of can for permission is informal.)

Could

Could is an auxiliary verb, a modal auxiliary verb. We use "could" to:

• talk about past possibility or ability

• make requests

Structure of Could

subject + could + main verb

The main verb is always the bare infinitive (infinitive without "to").

Notice that:

• Could is invariable. There is only one form of could.

• The main verb is always the bare infinitive.

Use of Could

could: Past Possibility or Ability

We use could to talk about what was possible in the past, what we were able or free to do:

• I could swim when I was 5 years old.

• My grandmother could speak seven languages.

• When we arrived home, we could not open the door. (...couldn't open the door.)

• Could you understand what he was saying?

We use could (positive) and couldn't (negative) for general ability in the past. But when we talk about one special occasion in the past, we use be able (positive) and couldn't (negative). Look at these examples: