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语法
Modality A1 A2

Ability and permission: can, could, may, and be able to

Express present, past, and general ability and ask or give permission with can, could, may, and be able to.

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图解

Ability or permission? Choose the job first

Choose the job first:

                 can / could / may / be able to
                           │
             ┌─────────────┴─────────────┐
             │                           │
        ABILITY                      PERMISSION
     “I have the skill”              “Is it allowed?”
             │                           │
   can + base verb              Can/Could/May I + base verb?
   be able to + base verb       can/may = give permission
             │                           │
   She can drive.               Can I sit here?
   She was able to find         May I see your passport?
   the address.

Base verb = plain verb:
   She can swim.
   ✗ She can to swim.

First choose the job: ability or permission. Then use the helper before the base verb, with no “to” after can/could/may.

Introduction

Ability and permission

English uses modal verbs to show what is possible in a person's situation. In this lesson, ability means a skill, power, time, or chance to do something. Permission means someone says that something is OK. Can is the most common word for both jobs in everyday English. Could helps with past ability and polite permission. May is more formal permission. Be able to is the flexible form when can does not fit, especially with future forms, infinitives, and some past successes.
Core 语法 A1 词汇 A1 Neutral

I can use this app.

Can expresses present ability in a simple everyday sentence.

语块拆解

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can use
modal_ability_frame
Can before a base verb expresses present ability or possibility.
整体记忆
this app
object
The thing the speaker is able to use.
Question 语法 A1 词汇 A1 Neutral

Can I sit here?

Can I...? is the most common neutral way to ask permission.

语块拆解

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Can I sit here
permission_question_frame
Can I...? asks for permission in everyday English.
整体记忆
Core logic

One word, two jobs

The same form can has two main jobs. For ability, the subject has the skill, strength, time, or chance to do something: She can drive. For permission, another person, rule, or situation opens the door: You can leave now. Context usually tells you the meaning. If the sentence is about a person's skill or practical possibility, hear ability. If it is about rules, asking, allowing, or refusing, hear permission. The basic logic is not the word alone; it is the word plus the situation.
Core 语法 A1 词汇 A1 Neutral

She can drive.

Context makes can mean ability here.

语块拆解

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She can drive
subject_modal_verb
The person has the skill or ability.
整体记忆
Core 语法 A1 词汇 A1 Neutral

You can leave now.

Context makes can mean permission here.

语块拆解

按语块读句子，别逐词读哦。

You can leave now
permission_statement
Can gives permission to do something.
整体记忆
Core pattern

Modal + base verb

Use can, could, or may before the base verb. They do not change for he, she, or it. In statements, use subject + modal + base verb, as in He can speak English. In questions, move the modal before the subject: Can we open the window? In negatives, add not after the modal: cannot, can't, could not, couldn't, may not. We can't park here. Can't is normal in speech and everyday writing; cannot is the full form and can sound stronger or more formal.
Core 语法 A1 词汇 A1 Neutral

He can speak English.

Can does not change after he, she, or it.

语块拆解

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can speak
modal_base_verb
Can is followed by the base verb, not to speak or speaks.
整体记忆
English
object
The language the person can speak.
Question 语法 A1 词汇 A1 Neutral

Can we open the window?

Can questions use can + subject + base verb.

语块拆解

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Can we open
modal_question_frame
Move can before the subject to make a question.
整体记忆
the window
object
The thing the speakers want to open.
Negative 语法 A1 词汇 A1 Neutral

We can't park here.

Can't is the common negative form of can.

语块拆解

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can't park here
negative_permission
Can't shows that permission or possibility is blocked.
整体记忆
Form variations

The flexible form: be able to

Be able to means 'have the ability or chance to do something.' It changes with tense and works after to. Use am/is/are able to for present, was/were able to for past, and will be able to for future. I am able to work tonight. She was able to find the address. We won't be able to come. After want, need, hope, or another structure with to, use to be able to: I want to be able to read this. In everyday present ability, can is usually shorter and more natural.
Core 语法 A2 词汇 A1 Neutral

I am able to work tonight.

Be able to can describe present ability, though can is often shorter.

语块拆解

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am able to work
be_able_present
Am able to expresses present ability or availability.
整体记忆
tonight
time
The time when the ability or availability exists.
Core 语法 A2 词汇 A2 Neutral

She was able to find the address.

Was able to works for past ability or a successful past action.

语块拆解

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was able to find
be_able_past
Was able to often shows success in one past situation.
整体记忆
the address
object
What she succeeded in finding.
Negative 语法 A2 词汇 A1 Neutral

We won't be able to come.

Use will be able to, not will can, for future ability.

语块拆解

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won't be able to come
future_negative_ability
Will not be able to is the normal future negative form because will can is not possible.
整体记忆
Core 语法 A2 词汇 A1 Neutral

I want to be able to read this.

To be able to works after verbs that need to.

语块拆解

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want to be able to read
infinitive_ability
After want to, use be able to, not can.
整体记忆
this
object
What the speaker wants to read.
Contrast

Past ability: could or was able to?

Could and was/were able to overlap, but they are not always the same. Use could for general ability in the past, especially skills or repeated situations: When I was six, I could read. For one successful action in the past, use was/were able to more often: After an hour, we were able to start the car. In negatives, couldn't can describe general inability or one failed action: I couldn't hear the teacher. This contrast is one of the most common boundaries for past ability.
Contrast 语法 A2 词汇 A1 Neutral

When I was six, I could read.

Could is natural for a past skill or repeated ability.

语块拆解

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could read
past_general_ability
Could expresses a general ability in the past.
整体记忆
When I was six
past_time_context
The time period when the ability existed.
Contrast 语法 A2 词汇 A2 Neutral

After an hour, we were able to start the car.

For one successful past action, was/were able to is usually clearer than could.

语块拆解

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were able to start
single_past_success
Were able to shows success in one past situation.
整体记忆
After an hour
time_after_effort
The effort or time before the success.
the car
object
What they succeeded in starting.
Negative 语法 A2 词汇 A1 Neutral

I couldn't hear the teacher.

Couldn't is flexible in past negative sentences.

语块拆解

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couldn't hear
past_negative_ability
Couldn't can describe general past inability or failure in one situation.
整体记忆
the teacher
object
The person the speaker could not hear.
Usage rules

Asking and giving permission

For permission, choose the form by situation. Can I...? is direct and common in daily life: Can I borrow your pen? Could I...? is softer and more polite: Could I ask a question? Here could is not past; it adds distance and politeness. May I...? is formal and common in official or careful speech: May I see your passport? To refuse permission, use can't or may not; may not sounds formal or like a rule: You may not enter. To give permission, can is common; may sounds more formal.
Question 语法 A1 词汇 A1 Neutral

Can I borrow your pen?

Can I...? is normal for everyday permission.

语块拆解

按语块读句子，别逐词读哦。

Can I borrow
neutral_permission_question
Can I...? is a common neutral permission frame.
整体记忆
your pen
object
The thing the speaker wants permission to use.
Question 语法 A2 词汇 A1 Neutral

Could I ask a question?

Could is not past here; it makes the request more polite.

语块拆解

按语块读句子，别逐词读哦。

Could I ask
polite_permission_question
Could I...? is a softer, more polite permission frame.
整体记忆
a question
object
What the speaker wants permission to ask.
Formal 语法 A2 词汇 A2 Formal

May I see your passport?

May I...? is more formal than Can I...?

语块拆解

按语块读句子，别逐词读哦。

May I see
formal_permission_question
May I...? is a formal permission frame.
整体记忆
your passport
object
The document the speaker asks to see.
Formal 语法 A2 词汇 A1 Formal

You may not enter.

May not is common in formal rules and notices.

语块拆解

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may not enter
formal_refusal
May not refuses permission in a formal rule.
整体记忆
Danger zone

Common form mistakes

Do not add to after a modal. Not She can to swim; say She can swim. Do not add -s to a modal. Not He cans cook; say He can cook. Do not use can after will or after to. Not I will can come; say I will be able to come. Also avoid stacking can and able together; choose can or be able to, not both. In questions, do not use do with can: say Can you come?, not Do you can come?
Mistake 语法 A1 词汇 A1 Neutral

She can to swim.

After can, do not use to before the main verb.

Corrected 语法 A1 词汇 A1 Neutral

She can swim.

The correct form is can + base verb.

语块拆解

按语块读句子，别逐词读哦。

can swim
correct_modal_base_verb
Can is followed directly by the base verb.
整体记忆
Summary

Quick choice map

Choose by job and time. For present or general ability, use can. For inability, use can't or cannot. For general past ability, use could; for a single past success, often use was/were able to. For future ability or after another to-form, use be able to. For permission, can is neutral, could is polite, and may is formal. Always put a base verb after can, could, and may. Remember that the modal can shows either ability or permission depending on context.
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