"Common sense" has been discussed throughout human history by philosophers
, and other people with large brains, yet it remains a curious and elusive subject because it is so uncommon.
The term is an English adaptation from an ancient Semitic language, but for simplicity's sake we'll call it Yiddish. "Common" is derived from the roots Kham and Ahn, which literally mean "Oy vey, come on you dimwitted klutz." Its earliest usage can be found in the Torah, when Moses and the Israelites were about to be recaptured by the Egyptians at the shore of the Red Sea:
Moses: O Lord Almighty, thou has led us this far in thy infinite wisdom and generous application of miracles, and we are most grateful.
God: Well then, why do you call upon me, if you believe I have done well for you? For I know you people too well to think that you would call upon me just to say "thanks," and therefore I ask that you tell me just what is bothering you now.
Moses: It is just so, my Lord, that the armies of the Pharaoh are closing in upon us, and we have found our escape blocked by a rather large and deep body of water (the Red Sea, no less), and not one of us is dumb enough to believe we can swim across.
God: Kham Ahn, Moses. I've got it all planned out; just jump into the water.
As the above passage indicates, using common sense generally yields great benefits. Unfortunately, laboratory tests have proven that jumping into the Red Sea rarely does the test subject any good, which suggests that common sense, even coming from God, tends to become outdated and new forms of common sense must be developed as needed.
This is made difficult, however, by the fact that common sense cannot be observed directly. Indeed, no one has actually seen common sense, but we infer that it exists because we can see when someone obviously isn't using it. As such, developing formal rules of common sense is extraordinarily difficult, and involves waiting for somebody to do something really stupid, and then one can try to determine what the commonly sensible thing to do might have been.
For example, suppose some fool lights his pants on fire with a match. He gets severely burned, and now has half of a pair of pants. Based on this, we can determine that if this person had used common sense, he would have taken his pants off first, soaked them with lighter fluid, and then set them on fire. This would have prevented the burning and gotten rid of the pants more efficiently.
Hopefully, the reader now has a better grasp of common sense and how to find it. Good luck!