Many years ago I came up with a common sense definition of common sense!
"Common sense is the WISE use of KNOWLEDGE!"
As you can see there are two components to common sense.
First and most important is wisdom! This comes directly from life experience gained by being involved in reality , not books, computers, and games.
The second component is knowledge. This pertains to 'facts' learned from both formal and informal sources.
So if you use good judgement based on wisdom to apply the knowledge you have acquired to any given set of circumstances you are using common sense.
Just common sense!!!
Here is the problem we face today. We have pushed the knowledge part of this way to far and the wisdom part has fallen WAY behind as we become more idealistic and less realistic in our life style.
There are MANY people today who go from birth to PHD (through college) with little to no real life experience and then they are considered MORE QUALIFIED than many people who have much more commonsense then they do just because they do not have a piece of paper (degree) to show 'how smart they are' . The move from the 'rural' life style to the "urban' life style is the main contributor to this problem.