This is one of the most common sentence endings in spoken Korean. By using this sentence ending, you imply that you are waiting for a response from the person that you are talking to. This originally comes from the combination of [ VERB + 그런데(geureonde) ]. 그런데 (geureonde) means “but,” “however,” and when combined with the verb of the previous sentence, it becomes the verb ending -ㄴ/는데 (-n/neunde) and you can add or not add 요 (yo) depending on the level of politeness of the sentence.
We can literally translate the sentence ending -ㄴ/는데(요) (-n/neunde(yo)) as “[Subject] + [Verb], but…” or “[Subject] + [Verb], however, ….” Although we still use it to express the original meaning, in spoken Korean, people use this sentence ending more often in order to show that they want some reaction or response from the other person. And we also often use it as a way to express surprise or to show exclamation.
So in English we can translate it as “Well, [Subject] + [Verb]” or “[Subject] + [Verb]… what do you think?”
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