Some day and someday both mean “a day” or “any one day.” The difference is that some day is a noun-phrase, while someday is an adverb, similar to today, tomorrow, or yesterday:
Is there some day when you will be available? (noun)
Someday, I will have the time. (adverb)
Can you specify some day that you can meet? (noun)
We should get together, someday. (adverb)
As you can see, someday usually comes at the beginning or end of a sentence, and modifies the verb or the entire sentence.
In contrast, some day can only appear as a noun, which you can see if you try substituting another noun in its place:
Is there some day /a time/ a day when you will be available?
Can you specify some day/some date that would be best to meet?
If you try this test for some day, you should always get it right.
More Examples of “Some day” in a Sentence
- Some day those magazines are going to be begging me for an interview.
- I’ll get hit by a bus some day, but Cecil will be eternal.
- I hope that you get to see the second one some day Jack.
- There is a risk that someone will some day delete them as unreferenced.
- Peter suggests that some day there could be peace between humans and synthetics.
More Examples of “Someday” in a Sentence
- Someone’s going to write a bitterly hilarious book about all of this someday.
- She hopes to someday work as a special education teacher for small children.
- And someday, he may be a coach on the bench like his dad.
- Some of them might be notable enough to someday have such an article.
- He hopes that someday the artist might see him in a different way.