This lesson explains the difference between ability and permission in English using can, could, be able to and be allowed to. You will learn when to use each form in present, past and polite requests, and how to express ability in different tenses.
Can: present ability or informal permission
Could: past ability, polite requests, or possibility
Be able to: ability in various tenses (including perfect and future)
Be allowed to: permission (formal or passive constructions)
Focus on whether the sentence expresses ability (can/could/able) or permission (allowed).
Table
Modals and Expressions of Ability/Permission
Form
Function
Example
can
Present ability / informal permission
I can speak with the client this afternoon.
could
Past ability / polite request / possibility
She could run five miles when she was younger. / Could you send the file?
be able to
Ability in various tenses (perfect/future) / completed actions
After training, he was able to finish the audit on time.
be allowed to
Permission (given or denied) / passive contexts
Employees are allowed to access the database with authorization.
Tip
Key rule: Ability vs Permission
Use the correct form depending on whether you talk about ability or permission, and on the tense:
Ability now: can + base verb (I can finish the report).
Ability in the past: could (general past ability) or was/were able to (specific completed action).
Polite requests: could or would for politeness (Could you review this?).
Permission: be allowed to (formal) or can for informal permission (You can leave early).
Use be able to for perfect and future forms (has been able to, will be able to).
Remember: 'could' = past ability in general; 'was/were able to' = succeeded in a past action.
Example
Examples in context
I can join the conference call at 3 PM.
She could solve the software issue before the meeting.
After the update, the engineer was able to deploy the application.
Staff are allowed to work from home two days a week.
Tip
Common mistakes
Watch out for these universal errors when using these modals and expressions:
Using 'can' to talk about a specific past success (use 'was/were able to' instead).
Confusing ability with permission — 'can' and 'be allowed to' are not always interchangeable.
Using 'could' for a completed past action when you should use 'was/were able to' to show the action succeeded.
Incorrect word order or double modals (e.g., 'can be able to' is incorrect).
Forgetting 'to' after 'able' (use 'be able to' + verb).
When in doubt, decide first: is it ability (use can/could/able) or permission (use be allowed to/can/may)?
Quiz
Choose the correct sentence:
Hint: Think about past completed actions and the correct past form.
Correct!
For a specific completed action in the past, use was/were able to rather than can or is able to.
Incorrect
The correct answer was: She was able to finish the report yesterday.
For a specific completed action in the past, use was/were able to rather than can or is able to.
Quiz
Complete: After the server reboot, the admin _____ restart the service.
Hint: Think about past ability after an event; use the correct past phrase for success.
Correct!
'Was able to' indicates a past ability that led to a completed action after an event.
Incorrect
The correct answer was: was able to
'Was able to' indicates a past ability that led to a completed action after an event.
Quiz
Which sentence is the most polite request?
Hint: Think about which modal is often used to soften a request politely.
Correct!
'Could' is commonly used for polite requests; it is more polite than 'can' in formal contexts.
Incorrect
The correct answer was: Could I use your laptop?
'Could' is commonly used for polite requests; it is more polite than 'can' in formal contexts.
Key Points
Vocabulary
can
modal verbCEFR A2//kæn//
Used to express present ability or informal permission.
I can attend the meeting this afternoon.
Vocabulary
could
modal verbCEFR B1//kʊd//
Indicates past ability, polite requests, or possibility.