~고서 (go-seo) – therefore/thus/so/which is why
Quite a simple grammar particle to learn but extremely useful.
The difference between ~고서 and just ~어/아/여/해서 is that there is only one meaning to ~고서.
~어/아/여/해서 sometimes can be interpreted as “after doing something”, which can be confusing sometimes.
So with ~고서, there is almost no confusion at all.
아침을 안 먹고서 지금은 너무 배고파 죽겠어.
I did not eat breakfast therefore I’m so hungry I feel like I’m dying.
친한 친구가 입원한 소식을 듣고서 병원으로 급하게 갔어.
I heard the news of my close friend getting hospitalised so I quickly went to the hospital.
I think this is wrong. Korean Grammar in Use Intermediate says it means the first action was completed before the second action started.