Complex Sentence (Câu phức)vsCompound Sentence (Câu ghép)

Clause hierarchy

Mệnh đề phụ phải bám vào một mệnh đề chính

1. 1
   SubordinatorAlthoughbáo hiệu quan hệ nhượng bộ
2. 2
   Dependent clausepublic transport is crowded
3. 3
   Main clausemany commuters still use itphần có thể đứng độc lập

Tóm tắt

Complex sentence = một independent clause (mệnh đề chính) + ít nhất một dependent clause (mệnh đề phụ), nối bằng subordinating conjunction (because, although, when, if, since, unless...) hoặc relative pronoun (who, which, that, where).

Tại sao quan trọng

Complex sentences là cấu trúc bắt buộc cho điểm cao trong IELTS:

IELTS Band	Đặc điểm cấu trúc câu
Band 5	Chủ yếu simple sentences, một số compound
Band 6	Dùng được compound sentences, bắt đầu có complex
Band 7	Dùng thành thạo complex sentences với variety
Band 8–9	Complex sentences phong phú, linh hoạt, ít lỗi

Theo Band Descriptors của IELTS, Band 7 yêu cầu: "uses a variety of complex structures". Không có complex sentences = không thể đạt Band 7.

Trong IELTS Writing Task 2: - ❌ Band 5: "There are many benefits of technology. Technology helps communication. It also helps education." - ✅ Band 7: "Although technology has transformed communication, its impact on education —especially in areas where access is limited— is still debated by researchers who emphasise the importance of equal opportunity."

Định nghĩa

Independent Clause (Main Clause)

Mệnh đề có thể đứng độc lập thành câu hoàn chỉnh: - The economy grew. - Students work hard. - Governments should invest in education.

Dependent Clause (Subordinate Clause)

Mệnh đề có S + V nhưng không đứng độc lập được vì bắt đầu bằng từ nối phụ: - because the economy grew → cần câu chính - although students work hard → cần câu chính - who invented the telephone → mô tả noun, cần câu chính

Complex Sentence

[Independent Clause] + [Dependent Clause] hoặc [Dependent Clause] + [Independent Clause]

(Khi dependent clause đứng đầu câu, dùng dấu phẩy sau nó)

Cấu trúc

Loại 1: Adverb Clause (Mệnh đề trạng ngữ)

Bắt đầu bằng subordinating conjunction, mô tả điều kiện, thời gian, lý do, mục đích, kết quả, nhượng bộ...

Vị trí: - Cuối câu: không cần dấu phẩy - She succeeded because she worked hard. - Đầu câu: dùng dấu phẩy sau dependent clause - Because she worked hard, she succeeded.

Loại	Subordinating Conjunctions	Ví dụ
Lý do (Reason)	because, since, as	She left because she was tired.
Nhượng bộ (Concession)	although, though, even though, while, whereas	Although it was raining, they continued.
Điều kiện (Condition)	if, unless, provided that, as long as, on condition that	If governments invest, outcomes improve.
Thời gian (Time)	when, while, after, before, until, as soon as, once, whenever	When she arrived, the meeting had started.
Mục đích (Purpose)	so that, in order that	She studied so that she could improve.
Kết quả (Result)	so...that, such...that	It was so hot that no one went outside.
Tương phản (Contrast)	whereas, while	Whereas cities expand, rural areas shrink.

Loại 2: Relative Clause (Mệnh đề quan hệ)

Bắt đầu bằng relative pronoun (who, whom, which, that, whose, where, when), mô tả một danh từ trong câu.

Relative Pronoun	Dùng cho	Ví dụ
who / whom	Người (who = subject, whom = object)	The student who studied hardest passed.
which	Vật, ý tưởng	The book which I borrowed was excellent.
that	Người hoặc vật (restrictive)	The house that he built is still standing.
whose	Sở hữu (người hoặc vật)	The student whose work was outstanding won.
where	Nơi chốn	The city where I grew up has changed.
when	Thời gian	The year when she graduated was 2020.

Hai loại relative clause:

Restrictive (Defining): Cần thiết để xác định danh từ — không có dấu phẩy - The students who study regularly tend to do well. (không phải tất cả sinh viên — chỉ những em học đều)

Non-restrictive (Non-defining): Thêm thông tin, không cần thiết — có dấu phẩy - My sister, who lives in London, is a doctor. (ta đã biết ai là chị gái — thêm thông tin phụ)

Lưu ý: that không dùng trong non-restrictive clause — phải dùng which hoặc who. - ❌ My car, that I bought last year, is already broken. - ✅ My car, which I bought last year, is already broken.

Loại 3: Noun Clause (Mệnh đề danh từ)

Mệnh đề đóng vai trò như một danh từ trong câu — làm chủ ngữ, tân ngữ, hoặc bổ ngữ.

Vị trí	Từ nối	Ví dụ
Chủ ngữ	What, That, Whether	What matters most is consistent effort.
Tân ngữ	that, what, whether, how, why, when	I believe that education is a right.
Sau linking verb	that, what	The problem is that funding is limited.

Cách dùng phổ biến

1. Adverb clauses — Thể hiện lập luận logic

Diễn đạt nguyên nhân (Band 7+): - Since many young people lack financial literacy, banks should offer educational programs. (since = because, formal hơn) - As the population continues to age, healthcare systems face increasing pressure.

Diễn đạt nhượng bộ — công nhận ý đối lập (Band 7 signature): - Although social media has numerous benefits, its negative effects on mental health cannot be ignored. - Even though technology creates jobs, it also displaces many workers. - While some argue that globalization benefits all nations, evidence suggests otherwise.

Diễn đạt điều kiện — lập luận có điều kiện: - Unless governments take immediate action, climate change will become irreversible. - Provided that adequate funding is available, the project could be highly successful.

2. Relative clauses — Mô tả và hạn định danh từ

Thêm thông tin về người/vật: - Countries that invest heavily in education tend to have stronger economies. - The researchers whose findings challenged the consensus faced significant scrutiny.

Non-restrictive — thêm chi tiết không thiết yếu: - Finland, which consistently tops international education rankings, invests significantly in teacher training.

3. Noun clauses — Diễn đạt ý kiến, niềm tin

Đặc biệt hữu ích trong IELTS Writing khi nêu quan điểm: - I believe that stricter regulations are necessary to address this issue. - What concerns me most is the long-term economic impact. - *It is widely accepted that education is the foundation of development. - The question is whether governments should intervene* in the market.

4. Phối hợp trong một câu

Complex sentences có thể chứa nhiều dependent clauses: - Although the government introduced reforms that aimed to reduce inequality*, many economists argue that the measures were insufficient. - Although... reforms → Adverb clause (nhượng bộ) - that aimed to reduce inequality → Relative clause - that the measures were insufficient* → Noun clause

Dấu hiệu nhận biết

Nhận ra Dependent Clause → Complex Sentence

Loại	Từ mở đầu
Adverb clause	because, since, as, although, though, even though, while, whereas, if, unless, when, whenever, before, after, until, once, so that, provided that, as long as
Relative clause	who, whom, which, that, whose, where, when (sau danh từ)
Noun clause	that, what, whether, if, how, why, when, where (làm subject/object)

Quy tắc nhanh: Nếu thấy một trong các từ trên và sau nó là S + V → đó là dependent clause → câu chứa nó là complex sentence.

Ví dụ

Phân tích câu thực tế

Câu 1:

"Although governments have made considerable efforts to reduce carbon emissions, scientists warn that climate change is accelerating at an unprecedented rate."

• "Although governments have made considerable efforts to reduce carbon emissions" → Dependent adverb clause (nhượng bộ, bắt đầu bằng although)
• "scientists warn" → Independent clause chính
• "that climate change is accelerating at an unprecedented rate" → Dependent noun clause (tân ngữ của warn)
• → Complex sentence với 2 dependent clauses

Câu 2:

"The cities that experience the fastest economic growth are often those where inequality is most severe."

• "The cities...are often those" → Independent clause
• "that experience the fastest economic growth" → Relative clause (restrictive, mô tả cities)
• "where inequality is most severe" → Relative clause (mô tả those)
• → Complex sentence với 2 relative clauses

Ví dụ IELTS Writing Task 2

Band 5 (simple + basic compound):

"Social media has benefits. It connects people. But it also has problems. Young people spend too much time on it."

Band 7 (complex sentences):

"Although social media has revolutionised the way people communicate, enabling individuals who live in different countries to maintain close relationships, there is growing concern that excessive use is damaging young people's mental health. Since the brain is still developing during adolescence, exposure to carefully curated online images — which often present an unrealistic ideal — can lead to anxiety and low self-esteem."

Phân tích câu 1: - Although...communicate → Adverb clause (nhượng bộ) - who live in different countries → Relative clause - that excessive use is damaging... → Noun clause

Phân tích câu 2: - Since the brain is still developing... → Adverb clause (lý do) - which often present an unrealistic ideal → Relative clause (non-restrictive, non-essential info)

Lỗi thường gặp

Lỗi 1: Sentence fragment — dùng dependent clause như câu đơn

• ❌ SAI: Although technology has many benefits. (dependent clause đứng một mình)
• ✅ ĐÚNG: Although technology has many benefits, it also poses risks.
• TẠI SAO: Dependent clause BẮT BUỘC có mệnh đề chính đi kèm. Đây là lỗi nghiêm trọng nhất trong IELTS Writing.

Lỗi 2: Dùng sai dấu phẩy với relative clause

• ❌ SAI: The students, who study hard, tend to succeed. (nếu muốn nói về tất cả sinh viên nói chung — restrictive)
• ✅ ĐÚNG: The students who study hard tend to succeed. (restrictive — chỉ những em học chăm)
• ❌ SAI: My brother who lives in Hanoi is a teacher. (nếu chỉ có một người anh — non-restrictive)
• ✅ ĐÚNG: My brother, who lives in Hanoi, is a teacher. (non-restrictive — thêm thông tin về người đã biết)
• TẠI SAO: Dấu phẩy thay đổi nghĩa của relative clause.

Lỗi 3: Dùng "that" trong non-restrictive relative clause

• ❌ SAI: The Eiffel Tower, that was built in 1889, is in Paris.
• ✅ ĐÚNG: The Eiffel Tower, which was built in 1889, is in Paris.
• TẠI SAO: that không dùng trong non-restrictive (non-defining) relative clause.

Lỗi 4: Dùng sai subordinating conjunction

• ❌ SAI: Despite she worked hard, she failed. (despite là preposition, không phải conjunction)
• ✅ ĐÚNG: Although she worked hard, she failed.
• ✅ ĐÚNG: Despite working hard, she failed. (despite + gerund/noun)
• ❌ SAI: Because of the economy is growing... (because of + noun, không phải clause)
• ✅ ĐÚNG: Because the economy is growing... (because + clause)
• ✅ ĐÚNG: Because of economic growth... (because of + noun phrase)
• TẠI SAO: Phân biệt because (conjunction + S + V) vs because of (preposition + noun/gerund); although (conjunction) vs despite/in spite of (preposition).

Lỗi 5: "Although... but..." — dùng hai liên từ đối lập

• ❌ SAI: Although she worked hard, but she failed.
• ✅ ĐÚNG: Although she worked hard, she failed.
• ✅ ĐÚNG: She worked hard, but she failed.
• TẠI SAO: although và but đều diễn đạt tương phản — dùng cả hai là thừa và sai ngữ pháp. Chọn một.

Lỗi 6: Thiếu dấu phẩy khi dependent clause đứng đầu

• ❌ SAI: Although the economy grew inequality remained high.
• ✅ ĐÚNG: Although the economy grew, inequality remained high.
• TẠI SAO: Khi dependent clause đứng trước independent clause, bắt buộc có dấu phẩy ngăn cách.

So sánh với

	Simple	Compound	Complex
Clauses	1 independent	2+ independent	1 independent + 1+ dependent
Liên từ	Không	FANBOYS	Subordinating conj. / relative pronoun
Ví dụ	She works.	She works hard, so she succeeds.	Because she works hard, she succeeds.
Hai vế bình đẳng?	—	Có	Không (dependent phụ thuộc main)
Emphasizes	Một ý	Hai ý bình đẳng	Một ý chính + ý phụ/bổ trợ
IELTS target	Band 5	Band 6	Band 7+

Khi nào dùng compound vs. complex: - Compound (She studied hard, so she passed): Hai ý ngang nhau, bình đẳng về tầm quan trọng - Complex (Because she studied hard, she passed): Một ý chính (kết quả), một ý phụ (lý do); hoặc khi muốn nhấn mạnh mối quan hệ cụ thể (nhượng bộ, điều kiện, thời gian...)

Lưu ý cho người học Việt Nam

Tiếng Việt có cấu trúc tương tự complex sentence — "Vì... nên...", "Mặc dù... nhưng...", "Khi... thì...". Tuy nhiên có hai điểm khác biệt quan trọng:

1. "Although... but..." trong tiếng Anh là SAI: - Tiếng Việt: "Mặc dù cô ấy học chăm, nhưng cô ấy không đỗ." → Tự nhiên hoàn toàn - Tiếng Anh: "Although she studied hard, she didn't pass." → Không có but - Lỗi này rất phổ biến ở người học Việt.

2. Despite vs. Although: - despite / in spite of + noun / gerund - although / though / even though + S + V

Tiếng Việt	Tiếng Anh (đúng)
Mặc dù có nhiều thách thức...	Despite the many challenges... (noun)
Mặc dù có nhiều thách thức...	Although there are many challenges... (clause)
❌ Mặc dù có nhiều thách thức...	Despite there are many challenges... (SAI)

Mẹo: Nếu sau "mặc dù" là chủ ngữ + động từ → dùng although. Nếu là danh từ/cụm danh từ → dùng despite/in spite of.

Ứng dụng trong IELTS

IELTS Speaking — Complex sentences tạo độ phức tạp ngữ pháp

Trong Speaking Part 3, các examiner tìm kiếm: - "I think that access to quality education should be considered a basic human right, which means governments have a responsibility to fund it." - "Although I understand why some people prefer online learning, I personally believe that face-to-face interaction is irreplaceable." - "Since technology is advancing so rapidly, it's difficult to predict what jobs will exist in 20 years."

IELTS Writing Task 2 — Building a Band 7 paragraph

Cấu trúc một luận điểm Band 7: 1. Topic sentence (có thể simple hoặc compound) 2. Explanation (complex sentence với because/since/as) 3. Concession (complex sentence với although/while/even though) 4. Example + elaboration (relative clause để thêm chi tiết)

Ví dụ:

"(1) Remote work has fundamentally altered the modern workplace. (2) Since employees no longer need to commute, they gain additional hours that can be used for personal development or family time. (3) While some workers thrive in home environments, others struggle with the isolation that remote work can create. (4) Countries where flexible work arrangements were common before the pandemic, such as the Netherlands, have reported higher levels of employee satisfaction than those where rigid office cultures persist."

Combining short sentences (cách thực hành)

From simple to complex (worked examples)

PHẦN 1: BẮT ĐẦU — CÂU ĐƠN

Câu đơn có một chủ ngữ và một động từ:

[Subject] + [Verb] + [Object/Complement].

• "Technology is useful."
• "Cities are growing."
• "Students use social media."
• "Exercise reduces stress."

Không sai, nhưng quá đơn giản. Hãy nâng cấp từng bước.

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PHẦN 2: BƯỚC 1 — THÊM LÝ DO

[Simple sentence] because / since / as [reason].

Transformation:

Câu đơn	+ Lý do
"Technology is useful."	"Technology is useful because it allows people to access information instantly."
"Cities are growing."	"Cities are growing as more people migrate from rural areas in search of better opportunities."
"Exercise reduces stress."	"Exercise reduces stress since it triggers the release of endorphins in the brain."

"Because" = lý do cụ thể, trực tiếp "Since" / "As" = lý do được xem là đã biết (slightly softer, academic)

Lưu ý: "Because" mạnh nhất trong ba từ — dùng khi lý do là trọng tâm của ý bạn muốn nói.

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PHẦN 3: BƯỚC 2 — THÊM KẾT QUẢ

[Simple sentence], so [result].
[Simple sentence]. Therefore, / As a result, / Consequently, [result].
[Simple sentence], which means (that) [result].

Transformation:

Câu đơn + lý do	+ Kết quả
"Technology allows instant access to information."	"...so people can now learn almost anything without leaving home."
"More people are moving to cities."	"...which means that urban infrastructure is under increasing strain."
"Exercise releases endorphins."	"As a result, regular physical activity can significantly improve mental wellbeing."

Before/after (đầy đủ):

• Before: "Exercise is good. It makes you feel better."
• After: "Regular exercise releases endorphins, which means that it can significantly improve mood and reduce feelings of anxiety — particularly for individuals under chronic stress."

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PHẦN 4: BƯỚC 3 — THÊM TƯƠNG PHẢN

[Main point], but [contrast].
Although [contrast], [main point].
While [side A], [side B].
[Main point]. However, [contrast].

Transformation:

Câu không có tương phản	+ Tương phản
"Technology is useful."	"Technology is useful, but it can also be a source of distraction and dependency."
"Cities offer opportunities."	"While cities offer greater career opportunities, they also come with higher living costs and significant social pressures."
"Social media connects people."	"Social media can connect people across vast distances. However, it has also been linked to rising rates of loneliness and anxiety, particularly among teenagers."

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PHẦN 5: BƯỚC 4 — THÊM RELATIVE CLAUSE

[Noun] + which/that [adds information about noun].
[Noun] + who [adds information about a person].
[Place] + where [adds information about location].
[Time] + when [adds information about a time].

Relative clause giúp bổ sung thông tin về danh từ ngay bên trong câu — không cần tách ra thành câu mới.

Transformation:

Câu không có relative clause	+ Relative clause
"Social media is popular."	"Social media, which has transformed how billions of people communicate, is now a dominant force in public discourse."
"Cities attract young people."	"Cities attract young people who are looking for career opportunities and a more dynamic social environment."
"The pandemic changed work culture."	"The pandemic, which forced millions to work from home, fundamentally altered expectations around workplace flexibility."

Thêm relative clause để thay thế câu thứ hai:

• Before: "Many countries face housing shortages. This creates social inequality."
• After: "Many countries face housing shortages, which contribute directly to rising social inequality and reduced social mobility."

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PHẦN 6: BƯỚC 5 — THÊM ĐIỀU KIỆN

[Main clause] if / unless / as long as / provided that [condition].
If [condition], [main clause].

Điều kiện thêm sắc thái và tính chính xác vào lập luận.

Transformation:

Câu không có điều kiện	+ Điều kiện
"Technology improves productivity."	"Technology can improve productivity significantly, provided that employees receive adequate training and the right tools."
"Remote work is beneficial."	"Remote work can be highly beneficial, as long as clear communication structures are maintained."
"Stricter laws will reduce crime."	"Stricter laws may reduce certain forms of crime, if they are enforced consistently and fairly."

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PHẦN 7: KẾT HỢP — CÂU PHỨC HOÀN CHỈNH

Bây giờ, kết hợp nhiều bước để tạo ra một câu phức thực sự có chiều sâu.

Transformation hoàn chỉnh — Example 1:

Câu đơn gốc: "Technology changes work."

Bước 1 (+reason): "Technology changes work because it automates many routine tasks."

Bước 2 (+result): "Technology automates many routine tasks, which means that workers must continually update their skills."

Bước 3 (+contrast): "While technology automates many routine tasks, which reduces labour costs for companies, it also demands that workers continually invest in upskilling."

Bước 4 (+condition): "While technology undoubtedly automates many routine tasks, reducing costs for businesses, its overall impact on employment is likely to be positive, provided that governments invest adequately in retraining programmes."

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Transformation hoàn chỉnh — Example 2:

Câu đơn gốc: "Cities are noisy."

+Lý do: "Cities are noisy because of the constant flow of traffic and large concentrations of people."

+Kết quả: "...noise pollution, which can disrupt sleep and contribute to chronic stress."

+Tương phản: "While urban environments are inevitably noisier than rural areas, which some residents find deeply disruptive, others argue that the energy and vibrancy of city life more than compensates for the drawback of noise."

+Điều kiện: "While urban noise levels are unlikely to decrease significantly in the near future, their health impacts can be mitigated if city planners prioritise green spaces, noise barriers, and pedestrianised zones in urban design."

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Transformation hoàn chỉnh — Example 3 (Speaking answer):

Q: "Do you think social media is good for society?"

Band 5 answer: "I think social media is good. It helps people communicate. But it also has problems."

Band 7 answer: "I think social media has real benefits, particularly in terms of enabling people to stay connected with friends and family across long distances. However, platforms that prioritise engagement over accuracy have also contributed to the spread of misinformation — which is a problem that governments and tech companies are increasingly struggling to address. On balance, I'd say the benefits outweigh the drawbacks, as long as users develop critical media literacy skills."

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PHẦN 8: CHECKLIST — Câu của bạn đã đủ phức chưa?

Yếu tố	Câu có chưa?
Ít nhất 1 mệnh đề phụ	□
Lý do hoặc kết quả được giải thích	□
Tương phản hoặc sắc thái được nêu	□
Relative clause hoặc participle phrase	□
Điều kiện hoặc nhượng bộ (nếu phù hợp)	□

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Lỗi thường gặp

Lỗi 1: Câu quá dài và mất mạch

Câu phức không phải là câu dài vô tội vạ. Nếu một câu có hơn 3-4 mệnh đề phụ, hãy tách ra.

• ❌ "Technology is useful because it helps people communicate, which means they can work remotely, which reduces costs, which is why companies prefer it."
• ✅ Chia thành 2 câu: "Technology enables remote communication, significantly reducing operational costs for businesses. As a result, it has become an increasingly attractive option for employers worldwide."

Lỗi 2: Thêm relative clause nhưng sai đại từ

• ❌ "The policy which it was introduced last year..."
• ✅ "The policy which was introduced last year..." / "The policy that was introduced last year..."

Lỗi 3: Quá nhiều "because" trong một đoạn

• Đa dạng hóa: because → since → as → given that → due to the fact that

Lỗi 4: "Although" + "but" trong cùng một câu

• ❌ "Although technology is useful, but it has drawbacks."
• ✅ "Although technology is useful, it has drawbacks." / "Technology is useful, but it has drawbacks."

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Bài tập luyện

Nâng cấp các câu đơn sau qua từng bước:

1. "Exercise is important." → Thêm lý do → Thêm kết quả
2. "Young people use social media." → Thêm relative clause → Thêm tương phản
3. "Governments should act." → Thêm điều kiện → Thêm nhượng bộ

Đáp án gợi ý:

1. "Exercise is important because it improves both physical and mental health. As a result, incorporating regular activity into daily routines has been shown to reduce the risk of numerous chronic diseases."

2. "Young people who have grown up with social media tend to use it as their primary source of news and social interaction. However, there are growing concerns about its impact on attention spans and the quality of real-world relationships."

3. "Governments should act decisively to address climate change, provided that such action is coordinated internationally and does not unfairly burden developing economies. While the short-term economic costs may be significant, the long-term consequences of inaction would be far more severe."

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Tóm tắt nhanh

TỪNG BƯỚC NÂNG CẤP CÂU:

BƯỚC 1 — +LÝ DO:
  "Technology is useful because it saves time."
  "...since / as [reason]"

BƯỚC 2 — +KẾT QUẢ:
  "...so people learn faster."
  "..., which means that / therefore / as a result, ..."

BƯỚC 3 — +TƯƠNG PHẢN:
  "..., but / although / while / however, ..."

BƯỚC 4 — +RELATIVE CLAUSE:
  "Social media, which connects billions of people, ..."
  "...a problem that governments must address."

BƯỚC 5 — +ĐIỀU KIỆN:
  "...provided that / if / as long as / unless ..."

KẾT HỢP:
  "While [A — contrast], [B — main point],
  which [result], provided that [condition]."

MỤC TIÊU: Câu CHÍNH XÁC và CÓ CHIỀU SÂU — không phải câu DÀI.

PHẦN 1: AND / BUT — Nối thêm thông tin hoặc tương phản

[Sentence A] + and/but + [Sentence B without repeated subject]

Before → After với "and":

❌ Trước	✅ Sau
"I study English. I also practice speaking."	"I study English and practice speaking regularly."
"She is kind. She is hardworking."	"She is kind and hardworking."
"He moved to the city. He found a job there."	"He moved to the city and found a job there."

Before → After với "but":

❌ Trước	✅ Sau
"The city is exciting. It is expensive."	"The city is exciting but expensive."
"I like coffee. I don't drink it at night."	"I like coffee but don't drink it at night."
"The plan was good. It didn't work."	"The plan was good but didn't work out."

Tránh lặp chủ ngữ khi dùng "and/but":

• ❌ "She studied hard. She passed the exam."
• ✅ "She studied hard and passed the exam." (bỏ "she" thứ hai vì cùng chủ ngữ)

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PHẦN 2: BECAUSE / SINCE / AS — Nối lý do

[Main idea] because/since/as [reason].
Because/Since/As [reason], [main idea].

Before → After với "because":

❌ Trước	✅ Sau
"I take the bus. My office is far away."	"I take the bus because my office is quite far from home."
"She was nervous. It was her first interview."	"She was nervous because it was her first interview."
"He started exercising. He wanted to feel healthier."	"He started exercising because he wanted to feel healthier."

"Since" và "as" — thay thế "because" (trang trọng hơn một chút):

• "Since public transport is unreliable, most people prefer to drive."
• "As the weather was so beautiful, we decided to walk instead."
• "Since she had lived there for ten years, she knew the city very well."

Lưu ý: "Since" cũng có nghĩa thời gian ("since 2010"). Ngữ cảnh thường làm rõ. Nếu muốn chắc chắn, dùng "because".

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PHẦN 3: WHO / WHICH / THAT — Relative Clauses

[Noun] + who/which/that + [additional information about that noun]

Relative clauses cho phép bạn thêm thông tin về một người hoặc vật ngay trong câu, thay vì tách thành câu riêng.

Before → After với "who":

❌ Trước	✅ Sau
"I have a teacher. She inspires me a lot."	"I have a teacher who inspires me a lot."
"My friend lives in London. He works in finance."	"My friend, who lives in London, works in finance."

Before → After với "which":

❌ Trước	✅ Sau
"I read a book. It changed my perspective."	"I read a book that changed my perspective."
"The city has great public transport. It makes commuting easy."	"The city has great public transport, which makes commuting easy."

Before → After với "that":

• "I found an app that helps me practice vocabulary every day."
• "She chose a career that she is genuinely passionate about."
• "This is the kind of problem that requires a long-term solution."

Mẹo: Dùng "who" cho người, "which" cho vật (non-defining), "that" cho người hoặc vật (defining — không có dấu phẩy).

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PHẦN 4: V-ING PHRASE — Nối hành động đồng thời hoặc nguyên nhân

[Main clause], + V-ing [additional action / reason].
V-ing [reason/context], [main clause].

Đây là cấu trúc nâng cao hơn nhưng rất tự nhiên và hiệu quả:

Before → After:

❌ Trước	✅ Sau
"I walk to work. I listen to podcasts at the same time."	"I walk to work, listening to podcasts along the way."
"She sat by the window. She was reading a book."	"She sat by the window, reading a book."
"He grew up in a small town. He learned to appreciate nature."	"Growing up in a small town, he learned to appreciate nature."
"I was tired. I still finished the report."	"Feeling tired, I still managed to finish the report."

Chú ý: Chủ ngữ của V-ing phrase phải là chủ ngữ của mệnh đề chính. Nếu khác, câu sẽ sai (dangling modifier): - ❌ "Walking home, the rain started." (mưa không thể "walking home") - ✅ "Walking home, I got caught in the rain."

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PHẦN 5: WHERE / WHEN — Thêm bối cảnh địa điểm hoặc thời gian

[Noun] + where [location information]
[Noun/Time] + when [time/circumstance information]

Before → After:

❌ Trước	✅ Sau
"I grew up in Hanoi. There were few tall buildings then."	"I grew up in Hanoi, where there were few tall buildings at the time."
"I remember a day. My father took me to the sea."	"I remember a day when my father took me to the sea for the first time."
"There's a café near my office. I go there every morning."	"There's a café near my office where I go every morning."

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PHẦN 6: BEFORE / AFTER / WHILE / WHEN — Nối sự kiện theo thứ tự thời gian

Before/After/When + [Sentence], [Main sentence].
[Main sentence] before/after/when + [Sentence].

Before → After:

❌ Trước	✅ Sau
"I finished work. Then I went to the gym."	"After finishing work, I went to the gym." / "I went to the gym after finishing work."
"I was a student. I lived in a dormitory."	"When I was a student, I lived in a dormitory."
"She arrived home. Then she made dinner."	"As soon as she arrived home, she made dinner."

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Áp dụng vào IELTS Speaking

Part 2 — Kể về trải nghiệm (before/after rõ ràng):

❌ Rời rạc:

"I visited Hội An. It was beautiful. There were many old buildings. I liked the lanterns. I took many photos."

✅ Câu kết hợp tự nhiên:

"I visited Hội An last year, which is a small ancient town in central Vietnam that is famous for its colourful lanterns and well-preserved architecture. I was genuinely amazed by the old buildings lining the riverside, where I spent most of the afternoon taking photos and exploring the local streets."

Part 3 — Phân tích có chiều sâu:

❌ Rời rạc:

"People use phones a lot. It is a problem. They don't talk to each other."

✅ Câu kết hợp:

"People use their phones so frequently that they often fail to engage with those around them, which is particularly noticeable in public spaces where people sit together without making any real conversation."

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Lỗi thường gặp

Lỗi 1: Dùng "which" khi nên dùng "who"

• ❌ "She is a teacher which works at my school."
• ✅ "She is a teacher who works at my school."

Lỗi 2: Nối quá nhiều ý với "and...and...and"

• ❌ "I went to the market and bought vegetables and came home and cooked dinner and watched TV."
• ✅ "I went to the market to buy vegetables, then came home to cook dinner before settling in for the evening."

Lỗi 3: V-ing phrase với sai chủ ngữ

• ❌ "Walking to school, the weather suddenly changed."
• ✅ "Walking to school, I noticed the weather suddenly change."

Lỗi 4: Lặp chủ ngữ khi không cần

• ❌ "She studied hard and she passed the exam."
• ✅ "She studied hard and passed the exam."

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Bài tập luyện

Nối hai câu thành một câu tự nhiên hơn:

1. "I have a sister. She lives in Australia." → ___
2. "I enjoy cooking. It helps me relax." → ___
3. "The film was long. It was very entertaining." → ___
4. "He moved to the city. He found a better job." → ___
5. "I remember a holiday. We went to the beach." → ___

Viết lại đoạn sau, kết hợp câu ngắn:

1. "I wake up early. I exercise. I feel better. I can focus at work."

Đáp án gợi ý

1. "I have a sister who lives in Australia."
2. "I enjoy cooking because it helps me relax." / "I enjoy cooking, which I find really relaxing."
3. "The film was long but very entertaining." / "Although it was long, the film was very entertaining."
4. "He moved to the city and found a better job." / "He moved to the city, where he found a better job."
5. "I remember a holiday when we went to the beach."
6. "I wake up early to exercise, which helps me feel better and focus more effectively at work." / "By waking up early and exercising, I find I can concentrate much better throughout the working day."

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Tóm tắt nhanh

AND / BUT → thêm thông tin hoặc tương phản (cùng chủ ngữ: bỏ "she/he/it" thứ hai):
  She studied and passed. | The city is exciting but expensive.

BECAUSE / SINCE / AS → giải thích lý do:
  I take the bus because my office is far away.

WHO / WHICH / THAT → thêm thông tin về người/vật:
  a teacher who inspires me | a book that changed my life
  great transport, which makes commuting easy

V-ING PHRASE → hành động đồng thời hoặc lý do:
  Walking to work, I listen to podcasts.
  Growing up in the countryside, she learned to love nature.
  → Chủ ngữ V-ing PHẢI là chủ ngữ của mệnh đề chính

WHERE / WHEN → bối cảnh địa điểm/thời gian:
  a café where I go every morning
  a day when everything changed

BEFORE / AFTER / WHILE:
  After finishing work, I went to the gym.
  When I was a student, I lived in a dormitory.

Bài tập luyện

Nối bằng cách phù hợp

1. "She failed the exam." + "She studied very hard." (nhượng bộ — although)
2. "The city lacks clean water." + "The government must invest in infrastructure." (kết quả — therefore)
3. "He is the researcher." + "His work changed our understanding of climate change." (relative clause — whose)
4. "Technology creates jobs." + "It eliminates many traditional ones." (tương phản — while)
5. "We act now." + "The effects will be irreversible." (điều kiện — unless)

Sửa lỗi

1. "Although she worked hard, but she didn't succeed."
2. "Despite she was tired, she continued working."
3. "The researchers, that discovered the vaccine, received a Nobel Prize."
4. "Because of the economy is growing, more jobs are available."
5. "When he arrived at the station. The train had already left."

Đáp án

Nối câu: 1. Although she studied very hard, she failed the exam. 2. The city lacks clean water; therefore, the government must invest in infrastructure. 3. He is the researcher whose work changed our understanding of climate change. 4. While technology creates jobs, it also eliminates many traditional ones. 5. Unless we act now, the effects will be irreversible.

Sửa lỗi: 1. → Although she worked hard, she didn't succeed. (bỏ but — không dùng although + but cùng lúc) 2. → Although she was tired, she continued working. (despite + noun/gerund; although + clause) 3. → The researchers who discovered the vaccine received a Nobel Prize. (non-restrictive: The researchers, who discovered...; restrictive: không dấu phẩy — that có thể dùng nếu restrictive) 4. → Because the economy is growing, more jobs are available. (because of + noun; because + S + V) 5. → When he arrived at the station, the train had already left. (dependent clause không đứng một mình)

Tóm tắt nhanh

1. Complex sentence = 1 independent clause + 1+ dependent clause
2. Ba loại dependent clause: adverb clause (because, although, if, when...), relative clause (who, which, that), noun clause (that, what, whether)
3. Dependent clause đứng đầu câu → dấu phẩy sau nó
4. Relative clause restrictive (xác định) → không dấu phẩy; non-restrictive (thêm thông tin) → có dấu phẩy
5. Lỗi phổ biến: although...but (chọn một), despite + clause (sai — dùng despite + noun/gerund), dependent clause đứng một mình
6. Complex sentences là yêu cầu bắt buộc cho IELTS Band 7+ (Grammatical Range & Accuracy)

Clause bridge

Hai mệnh đề độc lập cần một “cây cầu” đúng nghĩa

1. 1
   Independent clause 1The city is expensive.
2. 2
   Quan hệ ýcontrast → but / yet
3. 3
   Independent clause 2It offers many opportunities.
4. 4
   Câu ghépThe city is expensive, but it offers many opportunities.

Tóm tắt

Compound sentence = hai (hoặc nhiều) independent clauses nối với nhau bằng coordinating conjunction (for, and, nor, but, or, yet, so — FANBOYS), semicolon (;), hoặc conjunctive adverb (however, therefore, moreover...).

Tại sao quan trọng

Compound sentences là công cụ cơ bản để: - Kết nối ý liên quan mà không cần hai câu ngắn rời rạc - Thể hiện mối quan hệ logic giữa hai ý (tương phản, nguyên nhân-kết quả, bổ sung) - Tăng điểm Coherence trong IELTS Writing và tính lưu loát trong Speaking

Trong IELTS Writing: - ❌ Band 5: "Air pollution is a serious problem. Governments should act immediately." - ✅ Band 6+: "Air pollution is a serious problem, so governments should act immediately."

Compound sentence một mình không đủ cho Band 7+ (cần thêm complex sentences), nhưng là bước đệm quan trọng từ câu đơn lên câu phức.

Định nghĩa

Independent Clause (nhắc lại)

Nhóm từ có đủ chủ ngữ + vị ngữ, có thể đứng thành câu hoàn chỉnh: - She studies hard. - The economy grew. - Many people disagree.

Compound Sentence

Câu gồm ít nhất hai independent clauses được nối với nhau. Cả hai vế đều có thể đứng độc lập — chúng được kết hợp để thể hiện mối quan hệ ý nghĩa.

Quan trọng: Compound sentence không có dependent clause — đó là đặc điểm phân biệt với complex sentence.

Cấu trúc

Cách 1: Coordinating Conjunctions (FANBOYS)

[Independent Clause], [conjunction] [Independent Clause]

Dấu phẩy đặt trước conjunction (khi có ít nhất 5-6 từ ở mỗi vế):

Conjunction	Nghĩa	Ví dụ
For	vì, bởi vì (formal, giải thích lý do)	She left early, for she had an appointment.
And	và (bổ sung)	She studied hard, and she passed the exam.
Nor	cũng không (phủ định cả hai)	He didn't study, nor did he ask for help.
But	nhưng (tương phản)	She worked hard, but she didn't succeed.
Or	hoặc (lựa chọn)	You can study now, or you can regret later.
Yet	tuy nhiên (tương phản, formal hơn but)	The task was difficult, yet they completed it.
So	vì vậy (kết quả)	She prepared thoroughly, so she did well.

Mẹo nhớ FANBOYS: For – And – Nor – But – Or – Yet – So

Lưu ý về nor: Sau nor, cấu trúc đảo ngữ: He didn't call, nor did he text. (không phải nor he texted)

Cách 2: Semicolon (;)

[Independent Clause]; [Independent Clause]

Dùng khi hai ý liên quan chặt chẽ và cân bằng nhau: - She studies hard; she always gets top marks. - The problem is complex; simple solutions rarely work.

Semicolon = dấu phẩy "mạnh hơn". Không dùng conjunction khi dùng semicolon (không viết ; and, ; but).

Cách 3: Conjunctive Adverb (Trạng từ liên kết)

[Independent Clause]; [conjunctive adverb], [Independent Clause]

Conjunctive Adverb	Nghĩa	Ví dụ
however	tuy nhiên	The plan seemed good; however, it failed in practice.
therefore	vì vậy	She worked hard; therefore, she deserved the award.
moreover / furthermore	hơn nữa	The policy is costly; moreover, it is ineffective.
nevertheless / nonetheless	tuy vậy	The challenge was great; nevertheless, they succeeded.
otherwise	nếu không	Study hard; otherwise, you will fail.
consequently	do đó	Demand increased; consequently, prices rose.
meanwhile	trong khi đó	The economy shrank; meanwhile, unemployment soared.
thus	vì thế (formal)	Resources are limited; thus, prioritization is crucial.

Quan trọng: Conjunctive adverbs là trạng từ, không phải liên từ — không thể thay thế coordinating conjunction mà không có semicolon hoặc dấu chấm.

❌ SAI: She worked hard, however she failed. ✅ ĐÚNG: She worked hard; however, she failed. ✅ ĐÚNG: She worked hard. However, she failed.

Cách dùng phổ biến

1. Thể hiện mối quan hệ logic

Chọn conjunction/adverb phù hợp với mối quan hệ thực sự giữa hai ý:

Bổ sung (Addition): and, moreover, furthermore, in addition - Technology improves our lives, and it creates new challenges.

Tương phản (Contrast): but, yet, however, nevertheless, nonetheless - The economy grew, but inequality increased. - The plan was ambitious; however, it lacked funding.

Nguyên nhân-Kết quả (Cause-Effect): so, therefore, consequently, thus, for - Pollution levels rose, so the government imposed stricter regulations. - Demand fell; consequently, many factories closed.

Lựa chọn (Alternative): or, otherwise - We can invest in renewable energy, or we can face an energy crisis.

Nhấn mạnh thêm (Emphasis): nor - He didn't apologise, nor did he acknowledge the mistake.

2. Tránh câu ngắn đơn điệu

Thay vì viết nhiều câu ngắn:

"The internet is useful. It has some disadvantages. People should use it carefully."

Kết hợp bằng compound sentence:

"The internet is extremely useful, yet it has significant disadvantages, so people should use it carefully."

3. Punctuation (Dấu câu)

Với FANBOYS: - Hai vế dài (5+ từ): dùng dấu phẩy trước conjunction - She studied for months, and she finally passed the exam. - Hai vế rất ngắn: có thể bỏ dấu phẩy - She studied and she passed. (chấp nhận được, nhưng ít phổ biến trong writing)

Với semicolon: - Không dùng kèm coordinating conjunction: ❌ She studied hard; but she failed. - Có thể dùng kèm conjunctive adverb: ✅ She studied hard; however, she failed.

Dấu hiệu nhận biết

Nhận ra compound sentence khi thấy: 1. Hai chủ ngữ + động từ riêng biệt, nối với nhau 2. FANBOYS đứng giữa hai clauses (với dấu phẩy trước) 3. Semicolon nối hai clauses 4. Conjunctive adverb sau semicolon

Phân biệt compound vs. simple sentence với "and": - She and her friend studied hard. → Simple (một chủ ngữ ghép, một vị ngữ) - She studied hard, and her friend did too. → Compound (hai independent clauses)

Ví dụ

Phân tích câu thực tế

Câu 1:

"Social media connects people around the world, but it also spreads misinformation rapidly."

• "Social media connects people around the world" → Independent clause 1
• but → Coordinating conjunction (tương phản)
• "it also spreads misinformation rapidly" → Independent clause 2
• Mối quan hệ: tương phản (benefits vs. drawbacks)

Câu 2:

"The government introduced new environmental policies; however, many companies failed to comply."

• "The government introduced new environmental policies" → Independent clause 1
• ; → Semicolon
• however, → Conjunctive adverb
• "many companies failed to comply" → Independent clause 2
• Mối quan hệ: tương phản (action vs. response)

Ví dụ IELTS

(Writing Task 2 — tương phản và kết quả):

"Urbanisation brings significant economic benefits, yet it also places enormous pressure on infrastructure and social services. Cities attract investment and create jobs, so rural-to-urban migration continues to accelerate; consequently, urban planners must prepare for sustained population growth."

Phân tích: Câu 1 dùng yet (tương phản); Câu 2 dùng so (kết quả) + semicolon + consequently (kết quả tiếp theo) — 3 independent clauses được kết nối.

(Speaking Part 3):

"I think technology has made our lives easier in many ways, but it has also created new problems we didn't have before. People can now work from anywhere, so the traditional office is becoming less important; however, many employers still prefer face-to-face interaction."

Lỗi thường gặp

Lỗi 1: Comma splice — dùng chỉ dấu phẩy, không có conjunction

• ❌ SAI: She worked hard, she passed the exam.
• ✅ ĐÚNG: She worked hard, so she passed the exam.
• ✅ ĐÚNG: She worked hard; she passed the exam.
• TẠI SAO: Dấu phẩy không đủ mạnh để nối hai independent clauses. Phải có conjunction hoặc semicolon.

Lỗi 2: Dùng conjunctive adverb như coordinating conjunction

• ❌ SAI: She studied hard, however she failed.
• ✅ ĐÚNG: She studied hard; however, she failed.
• ✅ ĐÚNG: She studied hard. However, she failed.
• TẠI SAO: however/therefore/moreover là trạng từ, không phải liên từ. Chúng không thể nối hai clauses chỉ với dấu phẩy.

Lỗi 3: Run-on sentence — không có dấu câu hay conjunction

• ❌ SAI: The problem is serious the government must act now.
• ✅ ĐÚNG: The problem is serious, so the government must act now.
• TẠI SAO: Hai independent clauses không thể đứng cạnh nhau không có liên từ hay dấu câu.

Lỗi 4: Chọn sai conjunction — nghĩa không logic

• ❌ SAI: She studied hard, for she passed the exam. (for diễn giải lý do, không phải kết quả)
• ✅ ĐÚNG: She studied hard, so she passed the exam.
• ❌ SAI: Pollution is increasing, and the government should take action. (ý muốn nói tương phản/kết quả)
• ✅ ĐÚNG: Pollution is increasing, so the government should take action.
• TẠI SAO: Mỗi conjunction có nghĩa cụ thể — phải chọn đúng mối quan hệ logic.

Lỗi 5: Đặt sai dấu phẩy với FANBOYS

• ❌ SAI: She is smart but, she is not experienced.
• ✅ ĐÚNG: She is smart, but she is not experienced. (dấu phẩy trước conjunction, không sau)
• TẠI SAO: Dấu phẩy luôn đứng ngay trước coordinating conjunction.

Lỗi 6: Nhầm "for" (conjunction) với "for" (preposition)

• She left early, for she had a meeting. → for = conjunction (vì/bởi vì)
• She left early for a meeting. → for = preposition (để, vì)
• TẠI SAO: Khi for là conjunction, sau nó là một independent clause đầy đủ; khi là preposition, sau nó là noun phrase.

So sánh với

	Simple Sentence	Compound Sentence	Complex Sentence
Số clauses	1 independent	2+ independent	1 independent + 1+ dependent
Liên từ	Không	FANBOYS / semicolon	Subordinating conjunction (because, although, when...)
Ví dụ	She works hard.	She works hard, so she succeeds.	Because she works hard, she succeeds.
Cả hai vế bình đẳng?	—	Có	Không (dependent clause phụ thuộc)
IELTS Band	5	6	7+

Compound vs. Complex sentence — sự khác biệt quan trọng: - Compound: hai ý bình đẳng, cùng quan trọng như nhau - Complex: một ý chính + một ý phụ, ý phụ hỗ trợ ý chính

So sánh: - She studied hard, and she passed. → Compound (hai ý ngang nhau) - Because she studied hard, she passed. → Complex (lý do phụ trợ cho kết quả chính)

Lưu ý cho người học Việt Nam

Tiếng Việt có nhiều cách nối câu tương tự: "và", "nhưng", "vì vậy" — về nghĩa khá gần với FANBOYS. Tuy nhiên, người học hay mắc lỗi về dấu câu:

• Tiếng Việt: "Cô ấy học chăm, vì vậy cô ấy đậu." → "vì vậy" nối trực tiếp sau dấu phẩy
• Tiếng Anh: KHÔNG thể viết "She studied hard, therefore she passed."
• Phải dùng: "She studied hard; therefore, she passed." hoặc "She studied hard, so she passed."

Quy tắc đơn giản để nhớ: - and, but, or, so, yet, for, nor → dấu phẩy trước - however, therefore, moreover → dấu chấm phẩy trước

Ứng dụng trong IELTS

IELTS Speaking — Compound sentences tạo sự lưu loát

Thay vì dừng lại sau mỗi ý ngắn, nối mượt mà: - "I enjoy reading books, and I try to read at least one book a month." - "Social media can be addictive, but it also helps people stay connected." - "I used to dislike exercising; however, I've developed a love for it recently."

IELTS Writing Task 2 — Kết hợp compound + complex sentences

Chỉ dùng compound sentences (Band 6 ceiling):

"Education is important. It opens doors to better opportunities. Governments should invest in it."

Kết hợp compound + complex (Band 7+):

"Although education requires significant investment, the long-term economic returns are substantial, so governments should prioritise funding for schools and universities; moreover, an educated workforce is essential if a country wants to remain competitive globally."

(Complex: Although..., if...; Compound: so, moreover)

Bài tập luyện

Nối hai câu thành compound sentence

Dùng conjunction hoặc dấu câu phù hợp:

1. "The traffic was heavy." + "She arrived on time." (tương phản)
2. "The government raised taxes." + "Public spending was cut." (bổ sung)
3. "He didn't study." + "He didn't ask for help." (phủ định cả hai)
4. "Pollution is a serious issue." + "Immediate action is needed." (kết quả)
5. "She worked hard." + "She deserved the promotion." (kết quả/lý do)

Sửa lỗi

1. "Technology is advancing rapidly, however many people are left behind."
2. "She loves travelling she has visited 20 countries."
3. "The plan failed, for it succeeded later."
4. "He didn't sleep well, but he woke up energised, and he had a productive day, so he was happy."

Đáp án

Nối câu: 1. The traffic was heavy, yet she arrived on time. 2. The government raised taxes, and public spending was cut. 3. He didn't study, nor did he ask for help. 4. Pollution is a serious issue, so immediate action is needed. 5. She worked hard; therefore, she deserved the promotion. hoặc She worked hard, so she deserved the promotion.

Sửa lỗi: 1. → Technology is advancing rapidly; however, many people are left behind. (semicolon trước however) 2. → She loves travelling, and she has visited 20 countries. (run-on → thêm conjunction) 3. → The plan failed; however, it succeeded later. (for = vì/bởi vì, không phải tương phản) 4. → Câu đúng về ngữ pháp nhưng quá nhiều and. Viết lại: He didn't sleep well, but he woke up energised and had a productive day; consequently, he was happy. (tốt hơn cho IELTS)

Tóm tắt nhanh

1. Compound sentence = 2+ independent clauses nối với nhau
2. Ba cách nối: FANBOYS (dấu phẩy + conjunction) | Semicolon (;) | Conjunctive adverb (; however,)
3. FANBOYS: For, And, Nor, But, Or, Yet, So
4. Conjunctive adverbs (however, therefore, moreover) cần semicolon trước — không dùng chỉ dấu phẩy
5. Lỗi phổ biến: comma splice (She studied, she passed ❌) và dùng sai conjunction sai nghĩa
6. Compound sentence phù hợp Band 6; cần kết hợp thêm complex sentence cho Band 7+