one day/some day

one day 既可用于过去时,亦可用于将来时:

one day/the other day

1. I will take you there one day. 总有一天我会带你到那儿去的。

2. One day I met him in the street. 有一天我在街上遇见了他。

3. They leave unwanted objects in drawers, cupboards and attics for years, in the belief that they may one day need just those very things. (New Concept English, Book 3, L. 59) 他们将不需之物长年累月地置于抽屉、柜橱和阁楼里，相信有朝一日他们将需要这些东西。

而 some day 则只能用于将来时：

1. Some day you will be sorry about it. 你总有一天会对这件事感到后悔的。

2. He put away those iron scraps, hoping that they may come in useful some day. 他把那些碎铁皮收藏起来，希望这些东西也许有一天会有用处。