"someday" Vs "some day"

Question

You should come by some day.

You should come by someday.

Is there a difference between these? Are both technically correct?

Answer 1

You should use:

You should come by someday.

Some day means:

a single day that is unknown or unspecified

Whereas someday means:

refers to future events that will occur at an indefinite time

Therefore, some day would be appropriate.

Whereas, if you were referring to a specific time, e.g. next month, you would use some day as you are referring to a specific day next month, even if that day is unknown:

You should come by some day next month