Does 면서 need both subjects to be the same?

Question

가스를 사용하는 가정이 늘면서 가스 사고가 많이 발생하고 있다.

이것은 경제 상황이 나빠지면서 대학생들이 안정적인 직장을 원하게 된 것으로 보인다.

주식 시장이 활성화되면서 국내 경기가 더욱 호황을 누리고 있다.

According to all articles teaching Korean I have seen so far, and my textbooks, the subjects on both sides of 면서 have to be the same, like in "신문을 보면서 밥을 먹는다" or "자기는 놀면서 남만 시킨다".

But the three sentences above clearly don't follow this rule. Two of them are from my textbook and one of them is from a dictionary. Can someone explain the usage of 면서?

I have seen someone explaining the same problem in https://www.reddit.com/r/Korean/comments/9m04st/does_this_sentence_from_a_korean_book_make/. He says that 면서 sometimes can mean causation and the subjects on both sides do not need to be the same in that case. But it is not all that satisfactory to me because sentences like '주식 시장이 활성화되면서 국내 경기가 더욱 호황을 누리고 있다.' which he claims to mean causation, just seem to mean things that happen at the same time (the usual definition) to me. And still, why 100% grammar books say there have to be same subject?

Answer 1

"면서" can be used for both causation and simultaneous happening.

"신문을 보면서 밥을 먹는다" => It means "I read a newspaper and have a meal at the same time." In this case, the subjects on both sides are exactly the same. In fact, the sentence has an "implicit" subject, which is generally the speaker. If I say "그는 신문을 보면서 밥을 먹는다", it means "He reads a newspaper and has a meal at the same time." In any case, it has the same subject.

"주식 시장이 활성화되면서 국내 경기가 더욱 호황을 누리고 있다." => It means "The revitalization of the stock market is leading to the better domestic economics." This is causation. In this case, the subjects could be the same or different. In the example above, the first sentence is "The stock market is revitalizing." in which the subject is the stock market and the second sentence is "The domestic economics is getting better." in which the subject is the domestic economics. In this case, the meaning of the whole sentence is that "What is told in the first sentence is causing what is told in the second sentence."

If the grammar books you have say that there have to be the same subject, I think you can just ignore the explanation. Most Koreans use "면서" for both causation and simultaneous happening.