Vietnamese biết + verb means “know how to do” a learned activity: biết bơi “know how to swim,” biết lái xe “know how to drive,” and biết dùng máy này “know how to use this machine.” It describes acquired competence, not merely whether the action is possible at a particular moment.
That distinction is essential because English can compresses several meanings. “I can swim” usually describes a skill and is therefore Tôi biết bơi. “I can swim today because the pool is open” concerns circumstances and favors Hôm nay tôi có thể bơi vì hồ mở cửa. “I can swim here” may concern permission and favors Tôi được bơi ở đây when someone allows it.
The construction and its boundary
The basic pattern is subject + biết + activity predicate. Biết is also an ordinary verb meaning “know,” as in Tôi biết chuyện đó “I know about that.” With another verb directly after it, it often describes procedural knowledge.
Em gái tôi biết đọc từ năm tuổi.
My younger sister knew how to read from the age of five.
Anh có biết sửa xe máy không?
Do you know how to repair motorbikes?
Bà ngoại không biết dùng ứng dụng ngân hàng, nên tôi thường giúp bà.
Grandma does not know how to use the banking app, so I often help her.
The activity need not be physical. It can be linguistic, technical, social, or cognitive:
Chị ấy biết nói tiếng Việt và biết giải thích vấn đề rất rõ.
She knows how to speak Vietnamese and explain problems very clearly.
In the second phrase, biết giải thích may praise an acquired communicative ability rather than simply state that explanation is possible.
Skill, capacity, and opportunity
These three sentences answer different questions:
| Sentence | Meaning | Central question |
|---|---|---|
| Lan biết lái xe. | Lan has learned how to drive. | Does she have the skill? |
| Hôm nay Lan có thể lái xe. | Lan is able/available to drive today. | Do present circumstances allow it? |
| Hôm nay Lan được lái xe. | Lan is allowed or gets the opportunity to drive today. | Does she have permission or a granted opportunity? |
Tôi biết lái xe, nhưng hôm nay tôi không thể lái vì tay bị đau.
I know how to drive, but I cannot drive today because my arm is injured.
Minh biết nấu ăn nhưng hiếm khi được nấu trong bếp của nhà hàng.
Minh knows how to cook but rarely gets to cook in the restaurant kitchen.
The first person retains the skill despite temporary incapacity. Minh has the skill, but opportunity is limited. The next page treats Được for permission and opportunity in detail.
A compact map of nearby meanings
Vietnamese does not organize modality as a set of interchangeable auxiliary verbs. It distributes modal meaning across predicates, stance adverbs, and clause frames.
| Expression | What it contributes | Minimal contrast |
|---|---|---|
| phải | obligation or necessity | phải đi — must go |
| cần | goal-oriented need | cần làm — need to do |
| có thể | capacity or possibility | có thể đến — can/may come |
| được phép | explicit authorization | được phép vào — be permitted to enter |
| nên | advice or fitting conduct | nên nghỉ — should rest |
| chắc là | probable truth | chắc là đúng — is probably right |
Biết belongs beside this map but answers a different question: has the subject acquired the know-how?
Em biết bơi rồi, nhưng vẫn nên tập với huấn luyện viên trước khi bơi ngoài biển.
You know how to swim now, but you should still train with an instructor before swimming in the sea.
Having a skill does not erase advice, rules, or risk.
Negation and questions
Không biết + verb normally denies know-how: “not know how to.” It can also mean “do not know whether/how” when a following clause supplies an unknown decision or fact.
Tôi không biết trượt patin.
I do not know how to roller-skate.
Tôi không biết nên trả lời thế nào.
I do not know how I should answer.
The second is not a simple claim about a practiced skill. Nên trả lời thế nào is an embedded deliberative question: the speaker does not know what answer would be appropriate.
The usual yes–no question is có biết + verb + không?:
Bạn có biết cài máy in này không?
Do you know how to set up this printer?
Do not move không before the activity when your aim is merely to ask. Bạn có biết không cài máy in không? would be malformed or force an unintended analysis involving “not installing.”
Acquisition, time, and aspect
Because Vietnamese does not conjugate biết, time comes from context and time expressions. Đã biết + verb indicates that the skill has been acquired by the reference time. Biết... rồi often highlights the new state: “now knows how.” Chưa biết + verb means the skill has not yet been acquired.
Sau khóa học, tôi đã biết sơ cứu cơ bản.
After the course, I knew how to give basic first aid.
Con biết buộc dây giày rồi!
I know how to tie my shoelaces now!
Tôi chưa biết dùng công thức này, nhưng chiều nay đồng nghiệp sẽ hướng dẫn tôi.
I do not know how to use this formula yet, but a colleague will show me this afternoon.
Đã and rồi do not mechanically turn biết into an English past tense. They present acquisition or a changed state relative to context. Hồi đó tôi biết bơi can simply locate the possession of the skill in the past; Hồi đó tôi đã biết bơi rồi stresses that the skill was already acquired by then.
Skill claims and evidential stance
Statements about another person's skill may be softened or strengthened by evidence markers. These markers do not replace biết.
Dường như anh ấy biết đọc bản vẽ kỹ thuật.
It seems that he knows how to read technical drawings.
Cô ấy hẳn biết xử lý tình huống này; cô ấy đã làm công việc đó mười năm rồi.
She must surely know how to handle this situation; she has done that job for ten years.
Nam chắc là biết sửa lỗi này, còn tôi có lẽ phải hỏi bộ phận kỹ thuật.
Nam probably knows how to fix this error, while I will probably have to ask technical support.
Dường như marks appearance, hẳn a strong inference, chắc là high confidence, and có lẽ a tentative judgment. None of them says that an authority permits the action.
A dialogue where biết changes the answer
Hà: Cậu biết lái xe không?
Duy: Biết chứ, nhưng hôm nay tớ không được lấy xe của công ty.
Hà: Vậy cậu có thể lái xe của tớ không? Tớ đang đau đầu.
Duy: Có thể. Nhưng xe này lạ quá, cậu nên chỉ tớ cách mở phanh tay.
Hà first asks about learned skill. Duy says that he has it but lacks permission to use the company car. Hà's second question concerns practical willingness and capacity in the present situation. Replacing biết lái with được lái in the first question would ask about permission, not competence.
Politeness also affects what sounds natural. In an interview, Anh có biết sử dụng Excel không? is a neutral competence question. Asked of an older colleague whose expertise is obvious, the same wording may sound like a challenge; Anh có quen dùng Excel không ạ? can more gently ask about familiarity.
Common Mistakes
1. Translating every English can with có thể.
❌ Tôi có thể nói tiếng Việt từ nhỏ.
Wrong if the intended meaning is a learned language skill possessed since childhood.
✅ Tôi biết nói tiếng Việt từ nhỏ.
I have been able to speak Vietnamese since childhood.
The repair presents Vietnamese as acquired competence rather than present feasibility.
2. Using biết for temporary physical ability.
❌ Hôm nay tôi không biết đi bộ vì đau chân.
Incorrect for temporary incapacity: it says the speaker lacks the learned skill of walking.
✅ Hôm nay tôi không thể đi bộ vì đau chân.
I cannot walk today because my leg hurts.
3. Confusing skill with permission.
❌ Trẻ em biết vào phòng này khi có giáo viên.
Incorrect for a permission rule: biết means know how.
✅ Trẻ em được vào phòng này khi có giáo viên.
Children may enter this room when a teacher is present.
4. Misplacing negation in a yes–no question.
❌ Chị không biết dùng phần mềm này không?
Unnatural as the neutral question ‘Do you know how to use this software?’
✅ Chị có biết dùng phần mềm này không?
Do you know how to use this software?
The có... không frame asks neutrally; preverbal không biết would already assert or bias the question toward lack of knowledge.
Key Takeaways
- Biết + verb expresses learned know-how, not every kind of ability.
- Có thể concerns capacity or possibility; được concerns permission or opportunity.
- Không biết + verb denies skill, while chưa biết + verb says it has not yet been acquired.
- Đã biết and biết... rồi often highlight that learning has reached a new state.
- English can hides distinctions that Vietnamese makes overtly, so choose according to skill, circumstances, and authorization.
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- Có Thể for Possibility and AbilityA2 — Use có thể for what circumstances make possible, what someone is capable of doing, and what may be true.
- Được for Permission and OpportunityA2 — Use preverbal được for being allowed or getting the chance to act, and distinguish it from ability and explicit authorization.
- Mới as a Focus-Sensitive ParticleB1 — Go beyond the recency meaning of mới to express late thresholds, small quantities, prerequisites, and ‘only X’ focus.
- Đã...Chưa QuestionsA1 — Ask whether an expected event has been completed by the reference time with the aspect-sensitive frame đã...chưa.