Most of us have heard it said, in one form or another, that someone is "book smart, but lacks common sense." We've also heard people referred to as stupid, a derogatory term, to say the least, but it means that a person is deemed unintelligent. What that means is that a person can be extremely well educated, as in "book smart," but can lack the common sense it takes to live day to day without undesirable consequences. Here are two examples of consequences caused by lack of common sense and lack of intelligence. Both are true stories:
Case A - intelligent but lacking common sense.
A woman in her 40s has had the privilege of studying at the best schools, is sharp as a tack, and articulate. She runs the family business and conducts transactions that are difficult and complex with other business people. She can prepare tax returns for others with confidence that there will be no errors - she easily does most of the math in her head. Her studies in business and economics have prepared her for this type of work, and she thrives on the challenges of business deals and complicated transactions. She enjoys political involvement and is civic-minded. Her formal education is well-rounded and ongoing. There is no stupidity in this area. She is "book smart."
In her personal life, she makes bad choices and decisions. She procrastinates, takes risks with household expenses... spending on items that are unnecessary or beyond her means, often neglects her own appearance, family, and home. One summer, she makes a bad choice after believing in a deal that, to most people, sounds too good to be true. Ultimately, her decisions cost the family their entire property, a large piece of land that has been in the family for over 50 years. By letting herself be taken in by unscrupulous people, she shows her lack common sense; we may say she is naive, but nobody could accuse her of being stupid.
As a result, many outsiders who learn of the misfortune decide she's stupid and do not hesitate to say so. However, she is not at all stupid, but unfortunately, she has an extreme lack of common sense. The deal she makes is sure to turn out badly, but instead of considering the consequences if the deal falls through, she signs on the dotted line and loses everything, convinced all will be well. It isn't stupidity in her case. Ordinarily, she's quite astute in her dealings. In this case, it's lack of good common sense.
Case B - lacking intelligence and common sense
A man nearing 65 reveals his "stupid" side when he tries to handle a court case on his own without the aid of a lawyer. The man is not trained in law, and in fact, did not even finish high school. He has done manual labor throughout his life and has never attempted to obtain a GED nor any kind of specialized training. Of course, he demonstrates his lack of intelligence in many ways during his court appearance, and as a result he loses his case. His lack of education clearly shows as he is inarticulate and incapable of critical thinking skills. Although it is harsh and not politically correct, we may secretly consider him "stupid" for having tried to defend himself without even a good basic education.
In this second case, it is plain to see that lack of common sense and stupidity could easily be mistaken, one for the other. Also, this case may involve both the lack of common sense and lack of intelligence. The uneducated man refused legal help believing he could handle his defense himself. Despite warnings from people he spoke with prior to his court date, he insisted he could handle it himself because he would "know what to say." His refusals of help also showed a lack of common sense. It is easy to mistake his lack of common sense for his lack of intelligence, or perhaps assign both deficits to him.
Intelligence comes in different forms, but is generally determined by IQ and knowledge of the world in which we live; it is usually increased through formal education and experience. As already stated, lack of a reasonable degree of intelligence is cruelly referred to by some as stupidity.
Common sense is the natural ability to reason, manage, make good decisions, and conduct affairs by thinking things through and coming to reasonable conclusions. Common sense means one is "sensible," and can avoid many of life's common pitfalls by acting in sensible, responsible ways. Lack of common sense can get even the most intelligent person into huge amounts of trouble.
The best scenario for an individual is a good balance of both intelligence and common sense. This person will exhibit good intellectual ability and adequate amounts of common sense - some of both are necessary to avoid unnecessary trials and tribulations in life. For this person, the question of whether their actions were caused by lack of common sense or stupidity will seldom, if ever, be asked.