-고 and conjugation I think what they mean by "not conjugated for the tense" is that the verb before -고 doesn't change with the tense of the sentence. It is just how it works, not necessarily a restriction, as you say. Examples: - 친구는 결혼한 뒤 잘 살고 있었다: 살고 있다 -> 살고 있었다. The '살고' part remains the same. - 영수는 아이스크림이 먹고 싶었다: same. 먹고 싶다 -> 먹고 싶었다. - 영희는 자기도 모르게 그렇다고 대답하고 말았다: same. 하고 말다 -> 하고 말았다. All these are set phrases where -고 connects a main verb with an auxiliary verb that modifies the meaning. The two are tightly connected like idioms, and only the last part (the auxiliary verb) changes to suit the tense. But -고 can connect larger phrases and clauses too, in which case the verb before it can change. - 결국 그는 죽었고 나는 살아남았다 vs 결국 그는 죽고 나는 살아남았다. - 주식은 폭락했고 회사는 파산했다 vs 주식은 폭락하고 회사는 파산했다. Both versions of the above examples are correct and natural with a small difference in nuance. And the question of exactly which part changes for the tense doesn't just apply to -고. Some other verb connectives have their own similar characteristics. Here's tricky examples with -니까. - 친구에게 전화를 하니까 통화중이었다. (하다 before -니까 doesn't change. It connects sequential events tightly) - 친구에게 이야기 했으니까 걱정 안 해도 돼. (주다 before -니까 changes. Here two concepts are logically connection) Some connectives connect even more tightly than -고, and never changes with tense. - 공부를 열심히 해서 원하는 대학에 들어갔다. (verb before -아/어 almost never changes) - 공부를 열심히 해서 원하는 대학에 들어갈 거다. - 공부가 하기 싫었다 (verb before -기 좋다/싫다/편하다 never changes, as -기 form is like a noun)