① some day指“(將來)某一天”,用于將來時(shí)中。
I am sure he will succeed some day. 我敢肯定,他有一天會成功的。
② one day表示“(過去的)某一天”,也可表示“(將來)某一天”,可用于過去時(shí)或?qū)頃r(shí)中。
One day he walked through the forest. 一天,他步行穿過了那個(gè)森林。
They haven't seen each other for over twenty years,but they will meet again one day. 他們已經(jīng)20多年沒見面了,但是他們終有一天會見面的。