Common knowledge

I spend quite a bit of my time on the internet posting comments to various blogs, news sites and YouTube.  I like a good debate and I'm quite the devil's advocate at times (plus my ego loves to garner feedback and validation).  So if while in a comments section I find someone is making a "concrete" statement based on what I believe to be faulty logic, or shaky to non-existent "evidence", I will often question them on it, even if I ultimately agree with the conclusions they have come to.  This is because I am still trying to figure out things for myself.  I'm trying to find out if the conclusion or idea being presented is truly sound and well thought out before I make the decision to agree with it, discount it or to investigate it further.  I also hope that I am helping at least all small fraction of these people to question their own beliefs about things, to truly ask themselves: Do I really know this to be fact or am I just repeating a comment I heard someone else make, simply because it made sense to me at the time when that other person said it?

So when people make seemingly definitive and concrete statements about why something is "right" or "wrong"  -- particularly in the realm of ethics and values -- I will often ask them how they came to these conclusions.  Every so often people respond with comments about "common knowledge" or "common sense" or how the the action or comments of another person were "wrong" because they were  "outside the community standards of common decency" or "out of bounds" .  I will often ask these same people: Whose bounds?  Can you provide me a list of these "standards"?  How do you know what the "community" is thinking on any topic at any particular moment in time?

I have yet to receive a direct response to these questions.  Usually at best I get a link to a definition of "common knowledge" or the person will avoid these questions entirely and simply continue to provide arguments in favour or against the topic being discussed.

If there is someone out there in cyberspace who is reading this post and believes that there is such a thing as "common knowledge", "common sense" or "common decency", please do leave me a comment to explain how you know that something like this exists and where you are getting this information from. Who are the holders and arbiters of this "common knowledge", "common sense" or "common decency"? How is one able to "know" what this "common majority" of people think about things? Is there a website I can go to?

Then there are the semantics of what one defines as their "community" or who one defines as being a "common person"; when one speaks of the "majority" I have to ask: The majority of what? Middle class white people? Canadians? North Americans? People of the Western World? And are you including immigrants and aboriginals?  What group of people you are pulling this data from?  Is it just from speaking with people you have run into throughout your life?  And have you associated with a truly heterogeneous and equal mix of peoples of different ethnic and cultural backgrounds, economic classes, educations levels etc...?  Or is the "common person" someone who is like yourself in these respects?

I believe the idea of "common knowledge" is a figment of our imaginations, and that to different people "common knowledge" means different things, which kinda negates the idea of this knowledge being at all common.  Maybe others have some sort of mental ability that I have yet to comprehend, but I personally do not know what everyone else thinks; I have no psychic powers that I know of, and I have yet to find a person or group of persons that knows the whole truth about anything.  Even if I did know what the majority think about a particular topic at any one time, I also recognise that this doesn't mean that the belief or opinion of that majority is any more true than the beliefs of those in the minority.  I also recognise that ideas about what is "politically correct" or "morally objectionable" or "publicly acceptable" not only vary between individual people, or between larger cultural groups, but that the opinions of said individuals and cultural groups are ever evolving in themselves.  Just think of things we do and say today which would have been considered exceptionally rude, shocking or disgusting many years ago.

I'm not sure how to conclude this post, except by entreating any and all people who read it to leave me a comment about what they think about the concepts of "common knowledge".  Does such a thing truly exist?