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").

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

Notice that:

Could is invariable. There is only one form of could.
The main verb is always the bare infinitive.

The main verb is always the bare infinitive. We cannot say:

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 to (positive) and couldn't (negative). Look at these examples:

	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.

could: 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?

Be able to »