Quoted from https://quizlet.com/41134323/hongdae-grammar-prep-1-flash-cards/ *그런데 But/However/And *그렇지만 But/However If you want to contrast two sentences and say "A + but + B" you can choose to use either 그렇지만 or 그런데. If you want to introduce two actions or states that occurred one after another, and if the first sentence works as background information for the second sentence, only use 그런데. 어제 이거 샀어요. 그런데 정말 커요 그런데 means "but" but at the same time it can mean "and" as well. If what the speaker is implying is the meaning of "and", the entire sentence can mean "I bought this yesterday, and it's really big." or "I bought this yesterday, and as I found out, it's really big 어제 이거 샀어요. 그렇지만 정말 커요 그렇지만 means "but" or "however" so the speaker is contrasting the two facts- "having bought this yesterday" and "this being too big" - so it sounds like the speaker is disappointed that it's very big. As you can see, 그런데 can be used for a wider variety of meanings, and in addition to that, 그렇지만 has a very formal nuance to it, so in actual everyday conversations, 그런데 is much more commonly used than 그렇지만, and 그렇지만 is more commonly used in written language.

Literally they are like 'but' or 'however' and 'by the way' or 'anyway' But in daily life, Korean use both. 저는 아이스크림을 좋아하지만 지금은 이가 아파서 못 먹어요 I love ice cream but I can't eat it now because I have toothache 저는 아이스크림을 좋아해요 그런데 콜라도 좋아해요. I love ice cream. By the way, I also love coke