SENS COMMUN = COMMON SENSE
Popular phrases sometimes reflect what goes in deep in the hearts of all men. Among the Romans sensus communis meant not only common sense, but humanity, sensibility. Since we are not up to the Romans this word means only half as much to us as it did to them. It means only good sense, crude reason, the beginnings of reason, the first notion of ordinary things, a state midway between stupidity and intelligence. "This man has no common sense" is a great insult. "This man has common sense" is also an insult; it means that he is not exactly stupid, but that he lacks what is called mother wit. But where does this expression common sense come from if not from the senses? When they invented this word men admitted that nothing enters the mind but by the senses. Otherwise would they have used the word "sense" to denote ordinary reasoning?
It is sometimes said: "Common sense is very rare." What does this phrase mean? That in some men the beginnings of reason are halted in their progress by various prejudices, that a given man who judges very sensibly in one affair, will always grossly err in another. An Arab, who may well be a good calculator or a learned chemist or a precise astronomer, will nevertheless believe that Mohammed put half the moon into his sleeve.
Why will he surpass common sense in the three sciences I have mentioned, and fall below common sense when this half moon is in question? It is because in the first cases he saw with his own eyes, he has practised his intelligence; and in the last he saw with the eyes of others, closed his own, and perverted his innate common sense.
How can this strange mental disorder come about? How can ideas, which advance with so regular and firm a step in the brain in a great many subjects, limp so miserably in others a thousand times more palpable and easier to understand? This man always has the same principles of intelligence within him. There must therefore be a defective organ, just as it happens sometimes that the most refined gourmet can have a depraved taste for a certain kind of food.
How was the organ of this Arab, who sees half the moon in Mohammed's sleeve, vitiated? It was by fear. He had been told that if he did not believe in this sleeve his soul, when crossing the steep bridge immediately after his death, would fall for ever into the abyss. He had been told what is even worse: "If you ever doubt that sleeve a dervish will accuse you of impiety; another will prove to you that you are a madman who, having possible reason to believe, yet refuse to submit your haughty reason to the evidence; a third will denounce you to the little divan of a little province, and you will be legally impaled."
All this puts the good Arab, his wife, his sister, and all his little family into a state of terrified panic. They are sensible about all the rest, but here their imagination is wounded like Pascal's, who constantly saw a precipice beside his armchair. But does our Arab really believe in Mohammed's sleeve? No; he tries hard to believe; he says: "It is impossible, but it is true; I believe what I do not believe." A chaos of ideas, which he is afraid to resolve, forms in his head around this sleeve; and that is what lack of common sense really means.