François-Marie Arouet, better known by his nom de plume “Voltaire”, was an 18th century French Enlightenment writer, historian and philosopher, famous for his wit and his advocacy of freedom of speech. One of his most popular quotes is the beautifully simple: “Common sense is not so common.”
Common sense is what people in common would agree: that which they "sense" in common as their common natural understanding. It relates to the knowledge and experience most people have, or are believed to have by the person using the term.
The word common, by definition, suggests that common sense is held by a large number of people. But the idea that if most people think something makes sense then it must be sound judgment has been disproven time and time again. Further, it is often people who might be accused of not having common sense who prove that what is common sense is not only not sense, but also completely wrong. Plus, common sense is often used by people who don't have the real knowledge, expertise, or direct experience to actually make sound judgments.
