그때 널 잡았으면 좋았을 텐데

The line, explained

You are comfortable with Korean conditionals by now: -(으)면 means 'if'. What makes this line hurt is not the 'if' but what comes after it. 좋았을 텐데 refuses to finish. A beginner's translation is 'it would have been good', but a Korean listener hears 'it would have been good… and it wasn't, and I know whose fault that is.' That trailing quality is the lesson today.

Start at the front. 그때 is 그 (that) plus 때 (time, moment) — 'back then', pointing at one specific scene the singer cannot stop rewinding. 널 is 너 (you) with the object marker 를 fused in, the form you will see in almost every lyric sheet. 잡았으면 is 잡다, 'to grab, catch, hold onto', with the past marker -았- and the conditional -으면: 'if I had held onto you'. 잡다 is physical — a wrist, a sleeve, a hand at the door — which is exactly the image a ballad wants.

Now the ending. 텐데 comes from 터, an old noun meaning roughly 'the state of things, what is presumably so', plus -인데, the connective that means 'but' or 'and yet' and famously leaves sentences open. Together, -(으)ㄹ 텐데 says 'it would presumably be the case that…, but'. Add the past tense in front, 좋았을 텐데, and you have imagined a past that did not happen: 'it would have been good, but'. The 'but' has no second half. You are meant to supply it.

Register matters here. -(으)ㄹ 텐데 is not purely regret. Said about someone else in the present it becomes care: 추울 텐데 옷 입어 (you must be cold, put something on). Said about a plan it becomes mild caution: 비 올 텐데 (it'll rain, though). What stays constant is the speaker's stance: I am guessing, not stating, and I am leaving room. In a lyric about the past, that room fills up with everything the singer did not do.

Try hearing the line as three breaths. 그때 널 is the memory arriving. 잡았으면 is the hand that did not reach out. 좋았을 텐데 is the exhale. Swap 잡았으면 for 말했으면 (if I'd told you) or 돌아봤으면 (if I'd looked back) and the structure stays intact, which tells you the grammar is doing the emotional work. Once you can feel the difference between 좋았을 거야 (it would have been good, flat) and 좋았을 텐데 (it would have been good… ), you are reading lyrics the way Koreans do.