Common Knowledge

[rowanwitch]

Common knowledge means different things to different people... For example the vast majority understand how email addresses are formed.  But asked for help by an elderly acquaintance who was having problems emailing her daughter was brought home to me that common doesn't mean universal.   She had carefully written down the addresses her daughter told her. 

Format.  Marysmith95atgmail.com.   It's what she was told and she only understood correct spelling as she was told.  It would be very easy to look down on her lack of knowledge but it was information that only became relevant to her when she needed to use it.

Maybe you can think of other examples     of things you could assume to be common knowledge that might not be.