Modals - can/could

In this lesson, you will learn how to use can and could to talk about:

• ability
• permission
• requests
• possibility

Could is often more polite than can.

1. What Are Modal Verbs?

Modal verbs are special verbs that help us talk about:

• ability
• permission
• requests
• possibility

Important rules:

• Modal verbs do not change (no -s for he / she / it)
• They are followed by the base verb
• They do not use do / does

2. Can – Main Uses

2.1 Ability

Use can to talk about things you are able to do now.

Positive form

Subject + can + base verb

Examples:

• “I can swim.”
• “She can drive.”
• “They can speak English.”

Negative form

Subject + cannot / can’t + base verb

Examples:

• “I can’t swim.”
• “She can’t drive.”
• “They can’t speak English.”

Ability question form

Can + subject + base verb?

• “Can you swim?”

Short answers for ability questions:

• Yes → “Yes, I can.”
• No → “No, I can’t.”

2.2 Asking for Permission (Informal)

Use can to ask for permission and also to give permission in everyday situations.

Question form

Can + subject + base verb?

Examples (asking):

• “Can I sit here?”
• “Can we use your phone?”

Examples (giving permission):

• “Yes, you can.”
• “Sure, you can.”
• “Sorry, you can’t.”
• “No, I’m afraid not.”

2.3 Requests (Informal)

Use can to ask someone to do something.

Question form

Can + subject (you) + base verb?

Examples:

• “Can you help me?”
• “Can you repeat that, please?”

Can I... ? = permission

Can you... ? = request

2.4 Offers

Use can to offer help in everyday situations:

• “Can I help you?”
• “I can give you a lift.”

Can I help you? is an everyday offer. Could I help you? sounds more tentative or polite.

2.5 General possibility

Use can for something that is possible in general or sometimes happens:

• “It can be very cold here in winter.”
• “Buses can be late in winter.”

In a negative sentence, can’t can mean that something is not possible: “That can’t be true.”

3. Could – Main Uses

3.1 Ability in the Past

Use could to talk about general ability in the past. For example: “When I was five, I could swim.”

Positive form

Subject + could + base verb

Examples:

• “I could ride a bike when I was five.”
• “She could read when she was four.”

Negative form

Subject + could not / couldn’t + base verb

Examples:

• “I couldn’t ride a bike when I was five.”
• “She couldn’t read.”

We usually do not use could for one single successful action in the past. For one success, use was/were able to + base verb or managed to + base verb:

• “Yesterday, I was able to open the door.”
• “We managed to catch the last train.”

For one failed action, couldn’t is common. Compare:

• One success → “I was able to open the door.”
• One failure → “I couldn’t open the door.”

Use be able to when can is not possible in the form you need:

• “I’ll be able to drive next year.”
• “I’ve never been able to swim.”

Do not say “I will can drive.”

3.2 Permission in the Past

Use could to talk about permission that existed in the past:

• “When we were young, we could stay up late at weekends.”

Here, could means that staying up late was allowed. For permission now, use can: “We can stay up late tonight.”

3.3 Polite Requests

Use could to be more polite than can.

Question form

Could + subject + base verb?

Examples:

• “Could you help me, please?”
• “Could you open the door?”

3.4 Asking for Permission Politely

Use could to politely ask for permission.

Question form

Could + subject + base verb?

Examples:

• “Could I leave early today?”
• “Could we sit here?”

We often use could to ask for permission, but we usually answer with can: “Could I leave early?” — “Yes, you can.”

3.5 Suggestions and Offers

Use could to make a suggestion or offer help. It often means “this is one possible idea”.

• “We could go to the cinema.”
• “I could help you if you like.”

3.6 Present or Future Possibility

Use could for a possible present or future situation:

• “It could rain later.”
• “She could be at home.”
• “The train could be delayed.”

For a negative possibility, we often use might not: “It might not rain later.” Compare: “It could rain later” means rain is possible, but “It can’t rain later” means rain is impossible. This is like “That can’t be true” in section 2.5.

4. Can vs Could: Quick Summary

Function	Can	Could
ability	now: “I can swim.” / “I can’t swim.”	general past ability: “I could swim when I was five.” / “I couldn’t swim when I was five.” For one success, use “I was able to swim.”
permission and requests	informal: “Can I sit here?” / “You can’t sit here.”	more polite request: “Could I sit here?”
possibility	general possibility: “It can be cold here.” / “That can’t be true.”	possible present/future situation: “It could rain later.” / “It might not rain later.”