could

could — modal verb

1. used when talking about what a person or thing was able to do on a particular oc

1.情態動詞A1
釋義

used when talking about what a person or thing was able to do on a particular occasion in the past, or about a skill or natural ability someone had before now

例句

When I was six, I could already read simple storybooks by myself.

The swimmer could hold her breath for nearly two minutes.

同義詞
  • was able to

    more formal; also used for single past achievements where 'could' may sound unnatural

  • managed to

    emphasises effort or difficulty overcome in a specific situation

反義詞

文法句型

could + base form (affirmative)

could not / couldn't + base form (negative)

could + subject + base form? (question)

用法筆記

For the present tense, use 'can' instead of 'could'. In affirmative sentences about a single past achievement ('managed to'), 'was/were able to' is more common than 'could'.

常見錯誤

❌Yesterday I can swim across the lake.
✅Yesterday I could swim across the lake.
💡Use 'could' (not 'can') for past ability.
❌He could to run fast when he was young.
✅He could run fast when he was young.
💡Do not add 'to' after a modal verb.

2. used as a polite way to ask for permission to do something — softer and more hes

2.情態動詞A1
釋義

used as a polite way to ask for permission to do something — softer and more hesitant than 'can', which some listeners may find too direct

例句

Could I open the window? It feels a bit stuffy in here.

polite request for permission: Could I + verb

Could we leave a little earlier today? I have a doctor's appointment.

同義詞
  • can

    less polite, used in informal situations

  • may

    more formal, common in official or written contexts

文法句型

Could + I/we + base form? (asking for permission)

Could + I/we + possibly + base form? (more hesitant)

用法筆記

This sense always appears in question form. 'Could' is more polite than 'can', while 'may' is slightly more formal. In spoken English, 'Can I…?' is also acceptable but less courteous.

常見錯誤

❌Could I to borrow your pen?
✅Could I borrow your pen?
💡Do not add 'to' after a modal verb.

3. used as a courteous way of asking another person to take a particular action — s

3.情態動詞A1
釋義

used as a courteous way of asking another person to take a particular action — softer in tone than the more direct 'can'

例句

Could you please pass me the salt? I can barely reach it.

Could you please + verb (standard polite request)

Could you help me move this table to the other side of the room?

同義詞
  • can

    less polite; sounds more like an instruction than a request

  • would

    similar politeness level; 'would you' can sound slightly more hypothetical

文法句型

Could + you + please + base form? (polite request)

Could + you + possibly + base form? (more hesitant request)

用法筆記

Like sense 2, this always takes question form. The addressee is almost always 'you'. Adding 'please' makes the request warmer. To sound even more hesitant or apologetic, use 'Could you possibly…?'

常見錯誤

❌Could you to open the door?
✅Could you open the door?
💡Never insert 'to' between a modal and the main verb.

❌ 'Could you give me a hand?' (acceptable) — This is actually fine; just avoid 'to'.

4. used to say that something is possible or might happen, especially when you are

4.情態動詞A2
釋義

used to say that something is possible or might happen, especially when you are not certain or when the chance is not strong

例句

The traffic could be really bad on a Friday afternoon.

Don't throw that box away — it could be useful for storage.

possibility: could + be + adjective

同義詞
  • might

    similar level of possibility; often interchangeable with 'could'

  • may

    slightly more formal and can imply a marginally higher chance

  • can

    used for general possibility; 'could' sounds more tentative about a specific case

反義詞

文法句型

could + base form (present/future possibility)

could + have + past participle (past possibility that did not happen)

could + be + -ing (present possibility)

用法筆記

To express a stronger degree of certainty, use 'may' or 'might'. 'Could' suggests a real but not confidently expected possibility. For past possibilities that did not actually happen, use 'could have + past participle': 'You could have hurt yourself.'

常見錯誤

❌It could rains tomorrow.
✅It could rain tomorrow.
💡After a modal verb, use the base form of the main verb, not an -s form.

5. used to make a suggestion or offer an idea about what someone might do, either f

5.情態動詞A2
釋義

used to make a suggestion or offer an idea about what someone might do, either for their own benefit or as a shared plan

例句

You could try calling her again later this evening.

suggestion: you could + try + -ing

We could take the scenic route along the coast instead of the highway.

同義詞
  • might

    in suggestion contexts, 'might' sounds slightly more formal: 'You might want to try…'

  • should

    stronger and more directive; suggests a moral obligation or strong recommendation

文法句型

You/We could + base form (suggestion)

We could always + base form (alternative suggestion)

You could try + -ing / noun (suggestion with try)

用法筆記

Unlike sense 4 (POSSIBILITY), this sense offers a course of action the listener could choose. In questions ('Could we…?'), it overlaps with making a tentative suggestion. To make the suggestion stronger or more definite, use 'should' or 'ought to'.

常見錯誤

❌You could to try the new restaurant.
✅You could try the new restaurant.
💡Never add 'to' after 'could'.

6. expressing irritation or disappointment that a person failed to carry out an act

6.情態動詞B1
釋義

expressing irritation or disappointment that a person failed to carry out an action the speaker believes was reasonably expected of them

例句

You could have told me you were not coming to the party.

could have + past participle for past criticism

João could have asked before borrowing his brother's car.

同義詞
  • should have

    stronger sense of duty or moral obligation; 'could have' focuses on missed opportunity or reasonable expectation

文法句型

could + have + past participle (criticism about a past inaction)

could + at least + have + past participle (emphasising minimum expected action)

用法筆記

This sense almost always uses 'could have + past participle' referring to a past action that the speaker believes was expected. In speech, 'could have' is usually contracted to 'could've' (/ˈkʊd.əv/). The tone ranges from mild disappointment to strong anger depending on intonation.

常見錯誤

❌You could of told me earlier.
✅You could have told me earlier.
💡'Could of' is a common misspelling of the contracted form 'could've'. Never write 'of' after 'could'.