쉼표의 적절한 사용

By using commas properly, you can avoid making a run-on sentence (a sentence that has two or more complete sentences without appropriate conjunction or punctuation) and make your sentence a lot more clear.

1) name and title
When identifying something by name, after describing it more generally, use commas to separate out the name. Likewise, after stating someone's name, use commas to separate out their occupation.

• A government employee, Hong Gil-dong, said that....
• Professor Kim Chul-soo, the director of the Korean Center for Economic Development Research, said that...

But when you state a well-known person's official title that the person generally goes by, you don't need to separate out the title.

• Secretary of State Hillary Clinton said that... (o)
• Secretary of State, Hillary Clinton, said that... (x)

2) Parenthetical element
Use a comma before and after a parenthetical element to avoid confusion. Parenthetical element, or added/inserted clause, is a part of a sentence that can be removed without affecting the meaning of the original sentence.

• The leak was caused when the Deepwater Horizon rig, which had been drilling the well for BP, exploded April 20 and sank (Wall Street Journal, May 17, 2010): The sentence still makes sense without the italicized part, so you need a comma before and after it.
• Operation Rajprasong, which started on 14 May, has claimed the lives of at least 36 demonstrators (Guardian, May 17, 2010): Same thing here. The sentence still makes sense without the italicized part.
  

3) which, that, and comma
One of the most common mistakes I have seen: which vs. that

"A that B"는 명사의 의미를 좀더 분명하게 "제한"해 주기 위한 것이며 (A > B),
"A, which B"는 명사에 대한 "추가적인" 설명을 위한 것으로 (A=B) which앞에 쉼표를 써주어야 합니다.

• Jennifer likes purses that are expensive: 모든 핸드백이 다 비싼 것은 아니며 제니퍼는 핸드백 중에서도 비싼 핸드백만을 좋아하므로 that. (purses > expensive purses)
  
• Jennifer likes designer purses, which are expensive: 모든 명품 핸드백은 비싸며, 제니퍼는 그러한 명품 핸드백을 좋아한다는 의미이므로 쉼표 + which (designer purses = expensive purses)
• Designer purses, which are expensive, are what Jennifer likes: 이렇게 쓰면 which are expensive가 2번에서 설명한 parenthetical element가 됩니다.

4) such as
You need a comma if what follows "such as" is an example of what precedes it.
You don't need a comma if what follows "such as" narrows down what precedes it.

• I like movie stars, such as Brad Pitt and Tom Cruise: Brad Pitt and Tom Cruise are examples of movie stars. So you need a comma
• The house needs things such as furniture and bedding: Here, we don't know what category the "things" are. So "such as" narrows down what the "things" are, rather than giving examples of the "things."
  
• The house needs household goods, such as furniture and bedding: Now we know what category we are talking about (household goods), so you need a comma before "such as."

5) quotation and comma
Comma and period should come before the final quotation mark.

• “Starting today,” Justice Thomas wrote, “ours can count itself among the few in which judicial decree prevents voters from making that choice.”(New York Times, May 17, 2010)

6) series of items
When you list more than two items, use a comma to separate things. Make sure you use "and" only once before the last item. Some say that you don't need a comma before "and" but keep in mind that this is true only when your sentence is super clear. If there is any doubt that the last two items may be seen as one, use a comma.

• I like milk, egg, bread, and fruits for breakfast.
• I lost my key, got hit by a car, and broke up with my girlfriend. I hate my life.