If you stop to think about it, common knowledge is a strange concept. Depending upon how you look at it, one could argue that common knowledge is not really knowledge at all, but, rather, belief. For example, when I was a boy it was common knowledge that fish would bite better in the morning and afternoon, boys were smarter than girls, men smarter than women, white people were smarter than others, Jews were money-hungry and hard bargainers, if you ate watermelon seeds they would give you appendicitis, smoking would stunt your growth, girls could not go swimming when they had their periods, the genitals of Asian women were different from those of Caucasians, masturbation would cause hair to grow on your palms, black cats, broken mirrors, and walking under ladders were bad luck, four-leaf clovers were good luck, and if you put horse hairs in water and left them in the sun they would turn into snakes (I am exaggerating here for effect, but not as much as you might think).
Common knowledge, although related to common sense, is not truly the same thing. Common knowledge (like culture) is something that you possess mainly by being a member of a group of people who believe such things (although common knowledge can also vary from individual to individual). Common sense is more a directive to action. That is, it was common knowledge that if you stood behind a horse you might be kicked, common sense forbade you from doing so. Likewise, common knowledge told you black cats and broken mirrors were bad luck, common sense directed you to take some action, like aborting a trip or throwing a pinch of salt over your shoulder. At the moment it is common knowledge that Dick Cheney is a war criminal and was also involved in the treasonous act of “outing” a CIA agent. Common sense would demand that something be done about this (and even the law in this particular case), but as yet nothing has been.
In some cultures it is common knowledge that all illness and death is caused by either witchcraft or sorcery. In some it is common knowledge that you can foretell things by examining the entrails of chickens or goats, or certain crops can only be grown at certain times, or that camels require much more attention than horses, or you can only mature into an adult if you have taken a head, or a scalp, or counted coup. In still other places it is common knowledge that if you walk about at night you will encounter ghosts, or snakes, or evil demons. Some Pacific Islanders knew that if you sailed toward certain stars and followed certain currents and sailed at the right time of year, you would arrive safely at a distant island. In parts of the world you cannot attain adulthood without being circumcised or undergo a clitorectomy. My point here is that what is considered common knowledge varies a great deal from place to place, and even from individual to individual, and is in fact a strange mélange of both useful and useless information. I guess the parts that are truly useful do constitute knowledge, but how can so much of what we depend on and believe in be so utterly fanciful? It is common knowledge that allows us to act, and common sense that directs our actions (or is supposed to).
It should be clear that this human situation does not bode well for human action and interaction. Clifford Geertz said wisely and rather elegantly that as humans, “we are suspended in webs of significance that we ourselves have spun,” but he didn’t say much about the fact that these webs were so largely false. Is it any wonder we continue year after year beating and killing each other, often knowing next to nothing about our “enemies,” who know no more about us that we of them? Common sense would indicate how ridiculous this is, but common knowledge often overshadows common sense. Thus our common knowledge, more often than not simply false, tells us our enemies are “gooks,” or “krauts,” or “towel heads,” or “Japs,” and common sense is bypassed in favor of stupidity, greed, and blood lust. Even scientific knowledge, an equalizer of sorts, fails us when it comes to our interpersonal and intercultural affairs. I have no idea how we solve this intractable human dilemma, but massive educational efforts coordinated on a worldwide scale (with some agreed upon basic curriculum) might eventually have some effect, if, that is, we could stop fighting long enough to work on it. Think what the world could be like if all those billions upon billions were spent on universal education and international cooperation instead of more and more weapons of destruction. Unfortunately, although our common sense might think this a worthwhile idea, our respective common knowledge would doubtless make it impossible.