Could & Couldn't

Could and couldn’t are modal auxiliary verbs. Could and couldn’t are the past tense forms of can and can’t.

We use could and couldn’t to:

• talk about past possibility or ability
• make requests

Structure

subject + could/couldn’t + main verb

The main verb is always the infinitive without "to".

	subject	auxiliary verb	main verb
+	My grandmother	could	swim.
-	She	could not	walk.
		couldn't
?	Could	your grandmother	swim?

Uses

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 speak English when I was 5 years old.
• My grandmother could swim.
• When we arrived home, we 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 to (positive) and couldn't (negative).

	Past
	General	Specific Occasion
+	My grandmother could speak Spanish.	A man fell into the river yesterday. The police were able to save him.
-	My grandmother couldn't speak Spanish.	A man fell into the river yesterday. The police couldn't save him.

Requests

We often use could in a question to ask somebody to do something. The use of could in this way is fairly polite (formal):

• Could you tell me where the bank is, please?
• Could you send me a catalogue, please?