Someday vs. Some Day: What's the Difference?
Learn when someday means an unspecified future time and when some day refers to one particular day, with examples, rules, a quiz, and FAQs.
Someday is an adverb meaning at an unspecified time in the future: someday we will visit. Some day is a noun phrase referring to one particular but unidentified day: choose some day next week. If you can replace the expression with sometime, use someday; if a specific day could follow some, use two words.
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At 8:20 a.m., a scheduling email promises to send the contract “some day.” The writer means at an indefinite future time, not one day selected from a calendar, so the natural form is someday.
Someday vs. Some Day at a glance
| Word | Typical role | Meaning | Example |
|---|---|---|---|
| someday | Adverb | at an unspecified future time | Someday, the archive will be fully searchable. |
| some day | Determiner plus noun | one particular, unidentified day | Some day this week would work for the review. |
How to use someday
Someday modifies a verb and points vaguely to the future. It does not name a calendar unit and cannot normally take an adjective between its parts. It often expresses a hope, prediction, ambition, or event without a set date.
Someday, the archive will be fully searchable.
How to use some day
Some day treats day as a countable noun. The phrase can be expanded to some rainy day, some other day, or some day in June. Context may refer to the past or future, while someday usually points forward.
Some day this week would work for the review.
Rules that make the choice easier
Try sometime
If sometime preserves the meaning, choose someday: we will finish someday.
Look for a modified day
If an adjective or identifying phrase can describe day, keep two words: some quiet day next month.
Notice the time direction
Someday normally looks to the future; some day can identify an unknown day in the past or future.
Common mistakes to avoid
- Incorrect: Some day I will learn Italian. Preferred: Someday I will learn Italian.
- Do not combine the words when day is a countable calendar unit.
- Do not confuse someday with sometimes, which means on multiple occasions.
Quick practice
1. ___, we will publish the full archive.
Answer: Someday
2. Pick ___ after Tuesday.
Answer: some day
3. Which form can mean sometime?
Answer: someday
Frequently asked questions
What is the difference between someday and some day?
Someday means at an indefinite future time; some day means one particular day.
Is someday one word?
Yes, when it functions as an adverb meaning sometime in the future.
Is it someday next week or some day next week?
Some day next week is precise because day is selected from that week.
Can some day refer to the past?
Yes. It can mean an unidentified day in the past or future.