Which is more reassuring: “I’ll clean my room someday” or “I’ll clean my room some day?” It may seem like one little space doesn’t matter much, but when it comes to your future hopes and dreams (and possibly clean rooms), some day is a more realistic response than someday.
Both someday and some day are correct in different contexts. However, they’re not interchangeable.
- Someday - at some point in the future
- Some day - an unspecified day
Like sometime vs. some time, adding a space between some and day makes these words different parts of speech. Because they function differently in sentences, they have different meanings.
Someday is an adverb of time that refers to the future. You use it when describing any general time after today.
Synonyms of someday include:
- at some point
- in due course
- in the future
- one of these days
- sooner or later
If you’re wondering whether someday is the word you want to use, try replacing it with in the future or at some point. “I’ll clean my room someday” becomes “I’ll clean my room at some point” — which isn’t the most convincing promise.
You’d use someday when talking about an event that may happen. For example:
- Someday, I’d love to run my own business.
- He planned to write a novel someday.
- Our family will move someday, but for now we’re staying in town.
- We should take a trip together someday!
Some day is a noun phrase that refers to an actual, unspecified day. “I’ll clean my room some day next week” is more promising because the room will likely get clean in the next seven days.
Unlike someday, you use some day the same way you’d use a noun. You could replace some day with a day, or Wednesday, or any other noun that names a day.
- Let’s schedule our meeting for some day in October.
- I saw Howie some day last week, but I can’t remember when.
- Try to find some day next month for us to review the project.
- Isn't the wedding some day in April?
Like some day, one day is a noun phrase (the determiner one modifies day). But one day is also an English colloquialism meaning “in the future” — just like someday. So how do you use it?
You’re more likely to see one day as a way to reference a time in the future, especially one that’s more specific than someday.
- One day, I’d love to run my own business.
- He planned to write a novel one day.
However, you may also see one day as a noun phrase like some day when specifically talking about a single day.
It depends on the sentence. You can use one day as a (more specific) substitute for some day:
- Let’s schedule our meeting for one day in October.
- I saw Howie one day last week, but I can’t remember when.
Someday vs. some day is just one example of commonly confused words caused by a single press of the space bar. Need more hints to keep these words straight? You’ll find many more very similar — but also different — word pairs that follow the same pattern.