How to know when to use '아니면' or '또는' ?
Both them them are same but We use "아니면" in casual way like when we speak, and "또는" is used when we write down
They are commonly same so Koreans don't usually distinguish them.
아니면= if not
[ 아니다 (not be) + 면/으면 (If) ]
This one is casual.
When speaking with friends you can say 아님 which is same meaning but shorter.
Sounds more formal.
서울市 아니면 서울의 郊外?
Isnt 교회 church?
Its 교^외^.교회 DOES mean church, but 교외 means suburbs.
Suburbs of Seoul is 수도권 or 경기