Could

1. Overview & Concept

• What is it? Could is the past form of can, but in modern English it functions independently as a modal verb with several distinct meanings: past ability, polite requests, possibility, and conditional ability.
• Purpose: To describe what someone was able to do in the past, to make polite requests, and to speculate about possible situations.

2. Structure & Formula

3. Usage Rules

• Rule 1 — Past ability (general): Use could to describe a general ability someone had over a period in the past.
• When I was young, I could run very fast.
• She could speak three languages by the age of ten.

• ⚠️ For a single completed action in the past, use was able to, not could: She was able to finish the exam on time. (not could finish)

• Rule 2 — Polite requests: Could is more polite than can in requests.

• Could you help me with this, please?

• Could I borrow your pen?

• Rule 3 — Possibility (present/future): Could expresses a weaker possibility than might/may.

• There could be delays on the motorway.

• That could work — let's try it.

• Rule 4 — Conditional ability: In hypothetical or conditional sentences, could means "would be able to".

• If I had more time, I could learn the piano.

• Rule 5 — Could have + past participle: To talk about an unrealised past ability or missed possibility.

• You could have told me! I would have helped.
• We could have arrived earlier if we'd left at six.

4. Signal Words & Context

5. Common Pitfalls

6. Real-World Examples

1. When I was a child, I could ride a horse.
2. Could you turn down the music, please?
3. There could be a simpler solution to this problem.
4. She couldn't find her passport anywhere.
5. You could have emailed me — I didn't know.
6. Could I speak to the manager?
7. It could rain later, so take an umbrella.
8. He could play the violin at the age of four.
9. If we left now, we could still catch the last train.
10. They couldn't agree on a price, so the deal fell through.

7. Summary Table