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Unit 09
Can & Could
Ability, possibility & requests
Modal Verbs — Key Rules
Can and could are modal verbs. They are always followed by the base form of the verb. They never change form for any subject — no -s, no -ed, no -ing.
Form
| Type | Can | Could |
|---|---|---|
| Affirmative | I/you/he/she/it/we/they can swim. | I/you/he/she/it/we/they could swim. |
| Negative | I can't drive. / I cannot drive. | She couldn't come. |
| Question | Can you help me? | Could you wait a moment? |
| Short answer | Yes, I can. / No, I can't. | Yes, I could. / No, I couldn't. |
Can — Four Main Uses
| Use | Explanation | Example |
|---|---|---|
| Present ability | What you know how to do now | She can speak three languages. |
| General possibility | Something that is possible | It can get very cold here in winter. |
| Permission (informal) | Asking / giving permission | Can I open the window? / You can sit here. |
| Request (informal) | Asking someone to do something | Can you help me, please? |
Could — Three Main Uses
| Use | Explanation | Example |
|---|---|---|
| Past ability | What you could do in the past | I could swim when I was five. |
| Polite request | More polite than "can" | Could you pass the salt, please? |
| Possibility | Something that might be true | She could be at home now. |
Can vs Could for Requests
| Can (informal / direct) | Could (polite / softer) |
|---|---|
| Can you help me? | Could you help me, please? |
| Can I use your phone? | Could I use your phone? |
| Used with friends / family | Used in formal or polite situations |
Be Able To — When Can Is Not Possible
Can has no future or perfect form. Use be able to instead:
| Tense | ✅ Correct | ❌ Wrong |
|---|---|---|
| Future | I will be able to drive next year. | I will can drive. |
| Present Perfect | I haven't been able to sleep. | I haven't could sleep. |
| After another verb | I'd like to be able to cook. | I'd like to can cook. |
Could or Was Able To?
- Could = general ability in the past: I could swim when I was five.
- For one specific success in the past, use was/were able to or managed to: The road was closed, but we were able to find another way. (not
we could find) - In the negative, couldn't is fine for both: I couldn't find my keys this morning.
Annotated Examples
Subject
Verb
Auxiliary
Object
Adjective
Adverb
Preposition
Hover over any word to see its role.
subjectSheauxiliarycanverbplayobjectthe pianoadverbbeautifully.
↳ Can = present ability.
subjectIauxiliarycouldverbswimadverbwhen I was five.
↳ Could = past ability.
auxiliaryCouldsubjectyouverbhelpobjectmeobjectwith this?
↳ Could = polite request.
Common Mistakes
I can to swim.
→
I can swim.
No "to" after modal verbs — ever.
He cans play guitar.
→
He can play guitar.
"Can" never takes -s for any subject.
Could you to pass the salt?
→
Could you pass the salt?
No "to" after "could" either.
I couldn't to find a taxi.
→
I couldn't find a taxi.
No "to" after negative modals.
She can speaks English.
→
She can speak English.
After can/could always use the base form.
I will can come tomorrow.
→
I will be able to come tomorrow.
Two modals can't go together → will be able to.
After a long search, I could find my wallet.
→
After a long search, I was able to find my wallet.
One specific success → was able to / managed to.