I think the book is correct, but it could have provided more detail. Introducing a new topic doesn't automatically mean one has to use 이/가. You use it only when jumping directly into the new subject with 은/는 might confuse the listener, like: 1. the new topic is indeterminate (one of many possible instances), so needs specification. 2. the topic is too abruptly new, so the listener might be thrown off. For example, story book tales often start in this style. * 어느 산골 마을에 한 소녀가 있었다. 이 소녀는 어머니와 살고 있었다. ... (There was a girl in a mountainous village. The girl lived with her mother ...) The first sentence introduces this particular girl for the first time, so it uses "가". If you start directly with the second sentence, it might be confusing ("Who's this girl?"). And here's a TV news report scenario: 1. 오늘 오전에 서울 도심에 큰 불이 났습니다. 2. 이 화재는 건물 두 채를 모두 태운 뒤에야 진화됐습니다. 3. 정부는 경기 부양책의 일환으로 ... In #1, a new incident of fire is reported. To draw viewers' attention to this particular fire, 이 is used first. In #3, it changes to the new topic of the government's action, but still uses 는 instead of 가. Why? The reason is because the government is a subject everyone knows about already. We hear about it in the news almost every day, so there's no need to "introduce" it. So when the new topic is too unfamiliar, we introduce it with 이/가, to make it easy for them to follow. We can say 이/가 plays the role of signaling this fact. If the topic is already familiar (family, close friends, etc), we may not need it. An interesting thing to note is that in the above examples, the 이/가 in the first sentence translates to an indefinite article "a" in English. Introducing something with 이/가 first and continuing with 은/는 is thus similar to introducing something with "a" and then saying more about it with "the", as in "A fire broke out. The fire caused great damage". This is another way to see how they relate to each other.

You say 'topic', your quotation 'subject'. "마이클'이/은' 밤에 맥주와 치킨을 먹고 있었다. 갑자기 엠마'가' 왔다. 엠마'는' 마이클의 친구다. 마이클'이' 맥주와 치킨을 혼자만 먹자, 엠마'가' 말했다. "한 입만 줘!" 하지만 마이클'은' 주지 않았다. 엠마'는' 슬펐지만, 마이클'이' 엠마의 친구라서, 화를 내지 않았다. 대신 엠마'는' 노래를 불러 주었다. "잘~ 먹고~ 잘~ 살아라~" 마이클'은' 엠마'가' 너무 고마워서, 닭다리를 하나 주었다. 인생'은' 아름답다. 아직은 살 만하다, Let it be~" 은/는 is a controversial issue in Korean academia. Sorry for that. ㅠ,.ㅠ 은/는 때문에 나도 가끔 내 머리를 쥐어뜯어요.