Dear Copy Bitch: Should “back up” be one word or two?
Answer: It depends on how you’re using it. If you’re using it as a verb phrase, then it should be two words. If you’re using it as a noun meaning a physical duplicate, then it should be one.
1. Mr. IT Geek, please back up my Pulitzer Prize-worthy novel and George Clooney photo collection. (Back up is two words because it’s a verb phrase.)
2. Where’s the backup of my George Clooney photo collection? (Backup is one word, since it’s an actual physical duplicate.)