Ability and permission
Ability concerns capacity; permission concerns social authorization. The same form can express either, so context determines the interpretation.
01 · Concept foundation
Understand the terms before applying the rule
Each term below names a different grammatical object. Open examples and compare their function rather than memorising a Vietnamese translation alone.
ability/əˈbɪləti/
khả năng/năng lựcThe capacity of a person, system or process to perform an action.
The model can simulate waves.
Mô hình có thể mô phỏng sóng.
permission/pəˈmɪʃən/
sự cho phépAuthorization for an action, expressed with can, may or be allowed to depending on register and grammar.
May I use this dataset?
Tôi có thể dùng bộ dữ liệu này không?
be able to/biː ˈeɪbəl tuː/
cấu trúc be able toA semi-modal expression of ability that can inflect for tense and appear after other auxiliaries.
The team has been able to reduce the error.
Nhóm đã có thể giảm sai số.
Complete lesson scope
Do not stop at one formula
Present and general ability with can and be able to
Past general ability versus successful single events
Permission, prohibition and formal requests
Manage to, succeed in and be allowed to
Decision boundary: Could often describes general past ability; was/were able to or managed to is clearer for one successful event.
02 · Controlling rule
Can normally expresses present or general ability and ordinary permission. Could often expresses general past ability or a more tentative request. Use was/were able to, managed to or succeeded in for one achieved difficult event, and use be able to or be allowed/permitted/authorised to when future, perfect, infinitival or institutional forms are required. Ability describes competence; permission describes what rules or people allow.
can/could + V | be able/allowed/authorised to + V | managed to + V | succeeded in + V-ingAbility, opportunity, permission and authorisation
Distinguish what a person or system is capable of doing from what rules allow them to do, and choose forms that fit time, event type, register and institutional authority.
Ability concerns capacity; permission concerns authority
Can is efficient but semantically broad. Be able to, manage to, be allowed to, be permitted to and be authorised to make the source and type of possibility more explicit.
general capacity versus one successful event
physical/mental ability versus situational opportunity
informal permission versus formal authorisation
current, past, future and perfect forms
Present and general ability
Can normally expresses present or general capacity. Be able to is useful when the structure requires an infinitive, participle or explicit emphasis on capacity.
can + V | be able to + VUse can for ordinary present ability: The software can process large files.
Use be able to after another modal or infinitive marker: should be able to, hopes to be able to.
Distinguish inherent ability from opportunity: The drone can fly, but it cannot take off in this weather.
The solver can handle nonlinear boundary conditions.
The solver can handle nonlinear boundary conditions.
Can describes an established technical capability.
The new interface should be able to display larger datasets.
The new interface should be able to display larger datasets.
Should marks expectation; be able to supplies capacity after another modal.
Present/general ability
The system can detect anomalies.The system cannot detect weak signals.Can the system detect anomalies?- Use base form after can.
- Cannot is normally one word in formal writing.
Inflected ability
The team was able to finish.The team was not able to finish.Was the team able to finish?- Be carries tense and agreement.
- Useful for future, perfect and infinitive environments.
The selected form changes commitment and social force
Can I use the laboratory?
Direct but normally acceptable between equals or in routine service interaction.
Could I use the laboratory?
Creates distance and gives the listener more room to refuse.
May I use the laboratory?
Foregrounds the listener's authority to grant permission.
General ability versus one success
She could swim at five.
general past ability
She managed to swim across the channel.
one achieved difficult event
Use managed to/was able to when actual completion of one event matters.
Capacity versus permission
She can operate the crane.
she has the skill
She is authorised to operate the crane.
rules grant her authority
Ask whether the limiting factor is competence or institutional permission.
Routine versus formal permission
Can I leave early?
ordinary conversational request
May I leave the examination room?
formal authority-sensitive request
Choose according to relationship and setting, not a rule that may is always more correct.
Friends and routine service
- Prefer
- can, could
- Avoid
- authorised to for a simple favour
- Why
- Everyday interaction values natural brevity.
Rules, licences and safety
- Prefer
- be allowed/permitted/authorised to
- Avoid
- ambiguous can when legal status matters
- Why
- The wording should identify that authority comes from a rule or institution.
Research reporting
- Prefer
- can be used to, is capable of, enables X to
- Avoid
- can as an unexplained claim of universal performance
- Why
- Academic prose should specify conditions and the mechanism that enables the capability.
Let the modal control force and the lexical verb control precision
Describe technical capability
can/be able to + detect/process/resolve/simulateThe mesh can resolve the nearshore gradient.
Use a measurable technical verb rather than vague handle where possible.
Report achieved success
managed to / succeeded in + recover/identify/complete/obtainThe field team managed to obtain a complete tidal cycle.
This frame implies that completion was not automatic.
State institutional permission
be authorised/permitted/entitled to + access/modify/approve/operateThe principal investigator is authorised to approve data release.
The specialised verb should match the exact scope of authority.
Ability choice map
Choose by time and event type.
| Meaning | Preferred form | Example |
|---|---|---|
| present/general capacity | can | The tool can export CSV files. |
| general past capacity | could | The old system could run offline. |
| one successful event | managed to / was able to | We managed to recover the archive. |
| future/perfect ability | be able to | Users will be able to compare runs. |
Permission and authority
Register affects social meaning even when the propositional content is similar.
| Expression | Typical setting | Social effect |
|---|---|---|
| Can I...? | routine/casual | direct and natural |
| Could I...? | polite/less familiar | more tentative |
| May I...? | formal/authority-sensitive | recognises authority |
| be authorised to | legal/professional | formal status |
✕ Users will can export the results.
✓ Users will be able to export the results.
Two core modals cannot normally occupy the same finite slot; use be able to after will.
✕ After five attempts, we could recover the file.
✓ After five attempts, we managed to recover the file.
The sentence highlights one achieved difficult event, so managed to is clearer.
✕ Only licensed pilots can fly this aircraft.
✓ Only licensed pilots are allowed to fly this aircraft.
The intended restriction is legal permission, not physical ability.
✕ The team succeeded to recover the data.
✓ The team succeeded in recovering the data.
Succeed takes in + V-ing in this pattern.
Choose by meaning, evidence and relationship
1. Which sentence reports one difficult event that was actually completed?
2. Which form expresses future ability?
3. Which sentence identifies formal authority?
4. Which request is normally more tentative?
Describe one skill, one past successful event, one future capability and one formal permission from your work or study. Use four different structures and explain why each was selected.
Can/could is not used where a specific successful event requires managed to or was able to.
Ability and permission are not confused.
Future and perfect forms use be able to or be allowed to correctly.
The specialised verb matches the exact technical action or authority.
03 · Worked examples
Observe form, function and meaning together
The solver can handle nonlinear boundary conditions.
Bộ giải có thể xử lý điều kiện biên phi tuyến.
After three attempts, the team managed to recover the missing file.
Sau ba lần thử, nhóm đã khôi phục được tệp bị mất.
Only certified staff are authorised to modify the control settings.
Chỉ nhân viên được chứng nhận mới có thẩm quyền thay đổi cài đặt điều khiển.
After the upgrade, users will be able to export the results directly.
Sau khi nâng cấp, người dùng sẽ có thể xuất kết quả trực tiếp.
04 · High-risk contrast
Explain why one form fails, not only which answer is correct
Users will can export the results tomorrow.
Users will be able to export the results tomorrow.
Two core modals do not normally occupy the same finite slot; be able to supplies ability after future will.
05 · Mastery check
Apply the rule before marking the lesson complete
Which sentence is grammatically acceptable in the target system?
Which description best defines “ability”?
Which example is one of the verified target patterns in this lesson?
Which structural formula belongs to this lesson?
Complete all four checks, then submit a sentence for target-form feedback.
06 · IELTS Academic
Transfer grammar into a real communicative task
In Speaking, distinguish skills from permissions and use managed to for a specific successful experience. In academic and technical writing, prefer precise frames such as can detect, is capable of resolving, enables users to compare and is authorised to approve instead of a vague can do.
Explain how the selected modal changes truth commitment or social force.
Build affirmative, negative, question, perfect, progressive or passive forms without breaking the auxiliary order.
Distinguish two forms that can describe the same event but imply different evidence, authority or politeness.
Use a specialised verb that makes the proposed action or inference operationally precise.