there is sometimes in vulgar expressions an image of what passes in the heart of all men. “sensus communis” signified among the romans not only common sense, but also humanity and sensibility. as we are not equal to the romans, this word with us conveys not half what it did with them. it signifies only good sense — plain, straightforward reasoning — the first notion of ordinary things — a medium between dulness and intellect. to say, “that man has not common sense,” is a gross insult; while the expression, “that man has common sense,” is an affront also; it would imply that he was not quite stupid, but that he wanted intellect. but what is the meaning of common sense, if it be not sense? men, when they invented this term, supposed that nothing entered the mind except by the senses; otherwise would they have used the word “sense” to signify the result of the common faculty of reason?

it is said, sometimes, that common sense is very rare. what does this expression mean? that, in many men, dawning reason is arrested in its progress by some prejudices; that a man who judges reasonably on one affair will deceive himself grossly in another. the arab, who, besides being a good calculator, was a learned chemist and an exact astronomer, nevertheless believed that mahomet put half of the moon into his sleeve.

how is it that he was so much above common sense in the three sciences above mentioned, and beneath it when he proceeded to the subject of half the moon? it is because, in the first case, he had seen with his own eyes, and perfected his own intelligence; and, in the second, he had used the eyes of others, by shutting his own, and perverting the common sense within him.

how could this strange perversion of mind operate? how could the ideas which had so regular and firm a footing in his brain, on many subjects, halt on another a thousand times more palpable and easy to comprehend? this man had always the same principles of intelligence in him; he must have therefore possessed a vitiated organ, as it sometimes happens that the most delicate epicure has a depraved taste in regard to a particular kind of nourishment.

how did the organ of this arab, who saw half of the moon in mahomet’s sleeve, become disordered? — by fear. it had been told him that if he did not believe in this sleeve his soul, immediately after his death, in passing over the narrow bridge, would fall forever into the abyss. he was told much worse — if ever you doubt this sleeve, one dervish will treat you with ignominy; another will prove you mad, because, having all possible motives for credibility, you will not submit your superb reason to evidence; a third will refer you to the little divan of a small province, and you will be legally impaled.

all this produces a panic in the good arab, his wife, sister, and all his little family. they possess good sense in all the rest, but on this article their imagination is diseased like that of pascal, who continually saw a precipice near his couch. but did our arab really believe in the sleeve of mahomet? no; he endeavored to believe it; he said, “it is impossible, but true — i believe that which i do not credit.” he formed a chaos of ideas in his head in regard to this sleeve, which he feared to disentangle, and he gave up his common sense.