One test decides almost everything
Nearly every punctuation question in this domain collapses to a single question: is the material on each side of the punctuation an independent clause?
An independent clause has a subject and a finite verb and can stand alone as a sentence. A dependent clause has a subject and verb too, but a subordinator (because, although, when, if, since, while, that, which, who…) prevents it from standing alone.
The routine. Cover the punctuation. Read the words before it — can they be a sentence by themselves? Read the words after it — same question. Only then look at the answer choices.
Đừng đọc to lên rồi đoán chỗ ngắt hơi — tiếng Anh viết không đặt dấu theo hơi thở. Chỉ có một việc: xác định hai bên dấu có phải mệnh đề độc lập hay không. Toàn bộ nhóm câu này xoay quanh đúng câu hỏi đó, nên luyện phản xạ tách mệnh đề là luyện đúng chỗ.
The four legal joins
When both sides are independent clauses, exactly four punctuations are allowed.
- Period. The lab closed early. The samples were left in the freezer.
- Semicolon. The lab closed early; the samples were left in the freezer.
- Comma + coordinating conjunction (for, and, nor, but, or, yet, so). The lab closed early, so the samples were left in the freezer.
- Colon, when the first clause is independent and the second delivers what the first promises. The result was unambiguous: the culture had not grown.
The colony collapsed within a single seasonthe cause was never established.
- ,
- ;
- :
- , and
Both sides are independent, so (A) is a comma splice. A colon would announce that the second clause explains or delivers the first, but “the cause was never established” is a separate fact rather than the promised content, so (C) misreads the relation. (D) attaches and, which is legal but the sentence draws a contrast, not an addition. The semicolon joins the two statements and leaves the relation to the reader. Answer (B).
Khi hai vế đều độc lập, thường có nhiều hơn một cách nối đúng ngữ pháp. Lúc đó đề đang hỏi cách nào đúng nghĩa. Dấu hai chấm chỉ dùng khi vế sau trả lời đúng điều vế trước hứa; dấu phẩy cộng and chỉ dùng khi hai vế cùng chiều. Không hợp cả hai thì chọn dấu chấm phẩy.
Dấu chấm phẩy và dấu chấm giống hệt nhau về mặt ngữ pháp. Nếu đề cho cả hai làm hai phương án riêng thì cả hai đều sai, vì không thể có hai đáp án đúng — lúc đó đáp án nằm ở hai phương án còn lại.
The three illegal joins
Comma splice — two independent clauses joined by a bare comma. Wrong: The lab closed early, the samples were left in the freezer.
Run-on — two independent clauses with nothing between them.
Fragment — punctuating a dependent clause or a phrase as a full sentence. Wrong: Because the lab closed early.
Marine biologists tracked the pod for six weeksthe data they gathered reshaped the migration model.
- , and
- ,
- and,
- ;\ although
Both sides are independent. That rules out (B), a comma splice. (C) puts the comma after the conjunction, which is never correct. (D) adds although, which turns the second clause dependent and then wrongly precedes it with a semicolon. Only (A) is a legal join. Answer (A).
Conjunctive adverbs are not conjunctions
However, therefore, moreover, nevertheless, consequently, thus, instead, furthermore feel like joining words but have no joining power. A comma before one of them, with independent clauses on both sides, is still a comma splice.
The alloy resisted corrosion in salt waterhowever, it fractured under repeated stress.
- ,
- ;
- and
- but
However cannot join clauses, so (A) leaves a splice. (C) and (D) place a coordinating conjunction immediately before however, doubling the connectives. A semicolon joins the two independent clauses legally. Answer (B).
Mẹo nhớ: chỉ bảy từ for, and, nor, but, or, yet, so mới nối được hai mệnh đề độc lập bằng dấu phẩy. Mọi từ nối khác — kể cả however và therefore — đều cần dấu chấm hoặc dấu chấm phẩy đứng trước.
Supplements: the material you can delete
A supplement adds information that the sentence does not need grammatically. It is enclosed by a matching pair: two commas, two dashes, or two parentheses. The pair must match, and if the supplement is removed the sentence must still be complete.
The manuscriptdiscovered in a monastery archive in 1907contains the earliest known version of the poem.
- ,\ …\ ,
- ,\ …\ —
- —\ …\ ,
- (no punctuation)
Deleting the middle phrase leaves The manuscript contains the earliest known version of the poem, a complete sentence, so the phrase is a supplement and needs an enclosing pair. The pair must match, which eliminates (B) and (C). Answer (A).
Bẫy hay gặp nhất: mở bằng dấu phẩy, đóng bằng gạch ngang. Đọc lướt thấy rất tự nhiên, nhưng cặp không khớp là sai chắc chắn. Cứ thấy hai chỗ trống trong một câu là kiểm cặp đóng mở trước.
Long interrupters
The hardest items push the subject far from its verb, so a comma looks as if it belongs where the reader pauses.
A researcher whose fieldwork spanned three continents and whose notebooks fill an entire archive shelfpublished almost nothing during her lifetime.
- ,
- ;
- —
- (no punctuation)
The subject is A researcher; everything from whose to shelf modifies it; the verb is published. Nothing may separate a subject from its verb here. Answer (D).
Because the tide charts had not been updated since the harbour was dredgedthe survey team ran aground twice in a single morning.
- ;
- ,
- :
- (no punctuation)
The opening Because… clause is dependent, so a semicolon and a colon are both wrong, and an introductory dependent clause takes a comma before the main clause. Answer (B).