Here is what I think.^^' 1. when introduced a new topic, the subject marker(이/가)'s preferred. 사과<가> 있어요. 그 사과<는> 맛있어요. There is AN apple. THE apple is delicious. 사과<가>.... is a new topic. 사과<는>.... is the apple I mentioned already. 2. when interested in WHO, the subject marker's used. (some call it "identifier marker") WHO ate the apple? = 누<가> 사과를 먹었어요? I ate = 제<가> 먹었어요(focused on "I" not others) Did you eat the apple? = 사과를 먹었어요? I ate = 저<는> 먹었어요(focused on what you DID) 3.when talking about general things, the topic marker(은/는)'s often used. 사과<는> 빨개요 = Apples are red (generally) 사과<가> 검어요 = The apple is black (specific) (what a surprise! it's because you've never seen a black apple) There are some more, but it will be enough for introduction.^^' \^o^/

lilah, i am still figuring out that lesson. I somehow understand it but it's still a bit confusing. what lesson are you now?

Good explanation. Thanks for your input.

I admit that those particles are still confusing to me. But I have these points to remember which to use: -은/-는 1. emphasis on the thoughts of the speaker; listener is probably familiar to it and the speaker is adding to it 2. the topic is being compared/contrasted with something else 3. when starting a new topic or introducing a topic for the first time in paragraphs. 4. has a nuance of "about" something, "as for" something, or "unlike other things/different from other things" -이/-가 1. emphasis on the pure description of the subject 2. answers the questions "who" or "what" did something 3. has a nuance of "none other than", "nothing but"

in simple 은,는,이,가 are using behind a noun i sand message to you