1
Someday, + [subject + will + verb]
Someday, we will visit Mars.
有一天，我们将访问火星。
有一天；将来某天
先理解核心含义，再看它在真实句子里的用法。
有一天；将来某天
at some unspecified time in the future
Someday, we will visit Mars.
有一天，我们将访问火星。
将来某天；未来的某个不确定时间。
Sometime; at some unspecified time in the future.
I hope to visit Japan someday.
我希望有一天能去日本旅行。
Someday, technology may solve this problem.
有一天，技术或许能解决这个问题。
She believes she will become a writer someday.
她相信自己总有一天会成为作家。
Someday, we will visit Mars.
有一天，我们将访问火星。
She may become a doctor someday.
她有一天可能会成为医生。
someday 表示将来某个不确定的时间，常与 will、may 或 hope 等连用；注意不要与表示“某个日子”的 some day 混淆。
I hope someday we can meet again.
我希望有一天我们能再见面。
Not this
Someday I met my best friend at the park.
Use this
One day I met my best friend at the park.
someday 只表示将来的某个时候，不能用于过去；表达过去某一天要用 one day。
Not this
Someday is coming.
Use this
The future is coming.
someday 是副词，不能作主语；表示‘未来’要用名词 the future。
Not this
Let's meet someday next week.
Use this
Let's meet some day next week.
someday 是副词，意为‘将来某天’，不能放在 next week 前表示‘某一天’；这时要用名词短语 some day。
Focus on the distinctions below. Other candidates are kept compact until a reliable usage note is available.
不久的将来
Someday soon, we will travel to Japan.
不久的将来，我们会去日本旅行。
在未来的某一天
Someday in the future, you will look back and laugh.
在未来的某一天，你会回头看看然后笑起来。
也许某天
Maybe someday we'll meet again.
也许某天我们会再次相遇。
或许有一天
Someday perhaps I'll learn to play the piano.
或许有一天我会学弹钢琴。
总有一天（无论怎样）
Someday somehow, we'll find a solution.
总有一天，不管怎样，我们会找到解决办法的。
总有一天，也许那一天永远不会到来，我会请你帮我做一件事。
Someday I hope to understand this.
我希望有一天能明白这件事。
总有一天我们会找到它，那道彩虹连接，那些爱人和梦想家，还有我。
Someday people will live on Mars.
总有一天人类会在火星上生活。
Use someday naturally, then get feedback on meaning, tone, grammar, and phrasing.
Revisit a common error or keep this word in your review list.
把someday拆成some（某个）+day（天），记住“某一天”=将来的某个日子。
语域：neutral 常见场景：日常交谈、个人计划与愿望、一般书面叙述 someday 通常用于日常口语和一般书面语，比较常见于谈论未来的愿望或计划；在正式写作中较少出现，可换用更正式的说法。
The first syllable of 'someday' /ˈsʌmdeɪ/ sounds like 'some' /sʌm/, rhyming with 'sum' and 'drum' (all /ʌm/). 'sum' is a homophone of 'some'. The words 'day', 'today', and 'play' share the final /deɪ/ or /eɪ/ spelling and sound, but 'someday' is stressed on the first syllable, so these are lookalikes rather than true rhymes.
Dictionary facts from ECDICT, WIKTIONARY.