A subject-gap relative clause describes a noun through an action or state whose subject is left unspoken: người đang chờ ngoài cửa means “the person who is waiting outside.” The predicate đang chờ ngoài cửa has no pronounced subject inside the modifier because the head noun người supplies that role.
Vietnamese does not insert an obligatory equivalent of English who into that subject position. The relative follows the noun, and optional mà may mark its outer boundary. This page concentrates on recognizing and building the subject gap. Relatives in which a separate subject remains and the head corresponds to the missing object belong to Object-Gap Relative Clauses.
The subject is understood from the head noun
The basic frame is:
head noun + (mà) + + predicate
The blank shows the position interpreted as the subject of the predicate. It is an analytical symbol, not something written or pronounced.
Người đang đứng cạnh cửa sổ là bác sĩ trực tối nay.
The person standing by the window is the doctor on duty tonight.
Tôi muốn đổi chiếc đèn cứ nhấp nháy suốt đêm.
I want to replace the lamp that keeps flickering all night.
Những ai đã đăng ký trước sẽ nhận được email xác nhận.
Those who registered in advance will receive a confirmation email.
In each example, the material after the head begins with a predicate: đang đứng, cứ nhấp nháy, đã đăng ký. There is no separate noun phrase before that predicate. English supplies who or that as the grammatical subject; Vietnamese lets the head noun control an unspoken subject position.
Predicates, not just action verbs
The relative predicate may describe an action, state, property, identity, possession, or location. Vietnamese adjectives can serve directly as predicates, so no copular là is inserted before an ordinary property.
| Predicate type | Subject-gap relative | Register note |
|---|---|---|
| action | người đang sửa xe | neutral |
| property | căn phòng rộng nhất | neutral; no là |
| possession | ứng viên có nhiều kinh nghiệm | neutral |
| identity | người là trưởng nhóm | possible when identification itself is predicated; often a fuller appositive is smoother |
| careful complex modifier | giải pháp mà vẫn bảo đảm an toàn | mà can clarify the boundary |
Bọn mình nên chọn căn phòng rộng hơn và có nhiều ánh sáng tự nhiên.
We should choose the room that is larger and has plenty of natural light.
Công ty đang tìm ứng viên có thể bắt đầu làm việc ngay.
The company is looking for a candidate who can start work immediately.
The coordinated predicates rộng hơn and có nhiều ánh sáng tự nhiên share the same subject gap. In the second example, the modal có thể belongs to the relative predicate; it does not require a relative pronoun before it.
Mà with a subject gap
Subject-gap relatives strongly favor zero in short, neutral descriptions: người đang đợi, xe bị hỏng, quán mở muộn. Mà is possible when the modifier is long or deliberately contrastive, but it is more marked here than in many object-gap relatives and should not be inserted mechanically.
Tôi cần một người mà hiểu rõ cả kỹ thuật lẫn nhu cầu của khách hàng.
I need someone who understands both the technical side and the customer’s needs.
This is grammatical and explicitly bounded, though many speakers would also say một người hiểu rõ.... Mà remains a linker outside the gap; it is not the missing subject.
Finding the gap amid other clauses
The relative predicate can contain a condition, concession, cause, purpose, temporal clause, or reported-speech complement. Work from the outer noun inward instead of treating every connector as equivalent.
Chúng tôi cần một thiết bị mà nếu mất điện thì vẫn hoạt động được.
We need a device that will still work if the power goes out.
The head thiết bị is the understood subject of vẫn hoạt động được. The condition nếu mất điện has its own subject điện. The explicit pair nếu...thì is neutral and helps separate the two layers.
Cô ấy là người dù rất bận vẫn luôn trả lời tin nhắn của khách hàng.
She is someone who always answers clients’ messages even though she is very busy.
The same subject gap is understood with rất bận and luôn trả lời. Dù...vẫn packages concession inside the relative.
Đây là phần mềm được thiết kế để người khiếm thị có thể sử dụng dễ dàng hơn.
This is software designed so that visually impaired people can use it more easily.
The head phần mềm is the subject of passive được thiết kế, while để introduces a purpose clause with its own overt subject người khiếm thị. The purpose clause is not itself a relative.
Người mà Lan nói sẽ đến sau khi cuộc họp kết thúc là anh Quân.
The person who Lan said would come after the meeting ended is Quân.
This relative contains reported content. Lan is the subject of nói, but the head người is understood as the subject of sẽ đến. Vietnamese does not tense-shift sẽ merely because the report occurred earlier. Sau khi then introduces a temporal clause whose subject is cuộc họp.
Clause chains with a shared subject gap
Vietnamese frequently strings predicates together without repeating their shared subject. Inside a relative, this produces a clause chain describing what the head does in sequence.
Người đến sớm, mở cửa rồi bật điều hòa là chị Thu.
The person who arrived early, opened the door, and then turned on the air conditioner was Thu.
All three predicates share the gap linked to người. The comma does not automatically end the relative. The main predicate begins at là chị Thu. In speech, prosody helps; in formal or academic prose, a long chain may be clearer with người đã đến sớm rồi mở cửa và bật điều hòa or with two sentences.
Cause can also be embedded in the chain:
Người nhân viên vì bị kẹt xe nên đến muộn đã gọi điện báo trước.
The employee who arrived late because of traffic called ahead.
Here vì...nên organizes cause and result inside the relative. The final đã gọi báo trước is the main predicate. Without careful grouping, a listener could initially attach đã gọi to the relative too; mà or a pause after đến muộn can clarify the intended boundary.
Dialogue: subject gap versus a new subject
A: Ai sẽ dẫn buổi tập huấn? B: Chị đang trao đổi với giám đốc ở hành lang kia.
A: Who will lead the training? B: The woman who is talking with the director in the hallway over there.
B’s noun phrase has chị as the head and a subject-gap relative đang trao đổi với giám đốc. If B said chị mà giám đốc đang trao đổi cùng, the head would instead correspond to a non-subject role: “the woman the director is talking with.” The overt subject giám đốc changes the interpretation.
A: Anh chọn đề xuất nào? B: Đề xuất tuy ít tốn kém nhưng vẫn giải quyết được vấn đề cốt lõi.
A: Which proposal did you choose? B: The proposal that, although less expensive, still solves the core problem.
Both ít tốn kém and giải quyết được take the proposal as their understood subject. English inserts that before the concessive description; Vietnamese does not need one.
A quick decision aid
- Find the head noun.
- Ignore optional mà and inspect the following clause.
- If a separate noun phrase precedes the main verb, the head is probably not that verb’s subject; check for an object gap.
- If the predicate lacks an overt subject and describes the head, analyze a subject gap.
- In a chain, test whether the same head can naturally control each unexpressed subject.
The wider connector contrast remains useful: Tôi biết rằng anh ấy đến has a complement; người mà tôi gặp has a relative; nếu trời mưa thì ở nhà has a condition; vì bận nên tôi về sớm has cause and result. A subject gap is a relation inside a relative, not a property of rằng, nếu, or vì.
Common Mistakes
1. Inserting ai as English who
❌ Tôi cần người ai biết sửa máy in.
Incorrect: ai is an interrogative or indefinite form, not an ordinary relative pronoun.
✅ Tôi cần người biết sửa máy in.
I need someone who knows how to repair printers.
The head người directly supplies the missing subject of biết.
2. Repeating the subject after mà
❌ Người mà anh ấy đang đợi ngoài cửa là khách của tôi.
Incorrect for ‘the person who is waiting’: anh ấy creates a different overt subject and changes the structure.
✅ Người đang đợi ngoài cửa là khách của tôi.
The person who is waiting outside is my guest.
With anh ấy, the sentence instead tends toward “the person whom he is waiting for,” an object-gap interpretation.
3. Adding là before a property adjective
❌ Chúng tôi chọn căn hộ là yên tĩnh nhất.
Incorrect for an ordinary property relative: Vietnamese predicate adjectives do not need copular là.
✅ Chúng tôi chọn căn hộ yên tĩnh nhất.
We chose the apartment that is the quietest.
Use là for identification, not as a copy of English is before every adjective.
4. Mixing conditional and causal pairs
❌ Tôi cần thiết bị nếu quá nóng nên tự tắt.
Incorrect: nếu announces a condition, while nên is being used as though it completed that pair.
✅ Tôi cần thiết bị mà nếu quá nóng thì tự tắt.
I need a device that shuts itself off if it gets too hot.
The repair adds an explicit relative boundary and matches nếu with thì.
5. Overusing formal rằng in conversational reporting
Đây là người mà Mai nói rằng sẽ ghé chơi tối nay.
This is the person Mai said would drop by tonight. (grammatical, but formal for a casual chat)
✅ Đây là người Mai nói tối nay sẽ ghé chơi.
This is the person Mai said would drop by tonight.
In careful reporting, rằng is fine. In this short informal sentence, zero marking is smoother and the head remains the understood subject of sẽ ghé chơi.
Key Takeaways
- In a subject-gap relative, the head noun supplies an unspoken subject inside the following predicate.
- Mà may mark the relative boundary but does not fill the subject position.
- Predicate adjectives, verbs, passives, modals, and predicate chains can all occur after the gap.
- Inner connectors such as nếu...thì, dù...vẫn, vì...nên, để, khi, trước khi, and sau khi keep their own functions.
- If a distinct subject occurs before the relative’s main verb, test for an object-gap analysis on the next page.
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Start learning Vietnamese →Related Topics
- Mà in Relative ClausesB1 — Use mà as an optional boundary marker between a head noun and the Vietnamese relative clause that follows it.
- Object-Gap Relative ClausesB1 — Form Vietnamese relatives in which an overt subject acts on an unspoken object identified by the head noun.
- Reported Speech without Tense BackshiftB1 — Report earlier Vietnamese speech by preserving the event’s time relations rather than mechanically shifting verb tense as English does.
- Postnominal Relative ClausesB1 — Place a Vietnamese relative clause after its head noun and connect it to the wider system of explicit and implicit clause linking.