The circumstance which led the philosophers of Common Sense to traffic in this kind of article, was perhaps the notion that truths had a value in communication in proportion to their _importance_ to mankind. But that is a most mistaken idea. The most important truths have absolutely no value in communication. The truth that "each of us exists"--the truth "that each of us is the same person to-day that he was yesterday," the truth that "a material universe exists, and that we believe in its existence,"--all these are most important truths--most important things to know. It is difficult to see how we could get on without this knowledge. Yet they are not worth one straw in communication. And why not? Just for the same reason that atmospheric air, though absolutely indispensable to our existence, has no value whatever in exchange--this reason being that we can get, and have already got, both the air and the truths, in unlimited abundance for nothing,--and thanks to no man. Why _give_ a man what he has already _got_ to his heart's content--why _teach_ him what he already _knows_ even to repletion? It is not its importance, then, which confers upon truth its value in communication. In other words, it is a most superfluous civility for one man to impart truth to another, solely because it happens to be important. If the important truth be already perfectly well known to the recipient, and if the imparter of it is aware that the recipient knows it just as well as he does,--"thank you _for nothing_" is, we think, the mildest reply that could be made in the circumstances. The fact is, that the value of truth is measured by precisely the same standard which determines the value of wealth. This standard is in neither case the importance of the article,--it is always its difficulty of attainment,--its cost of production. Has _labour_ been expended on its formation or acquisition; then the article, if a material commodity, has a value in exchange--if a truth, it has a value in communication. Has no labour been bestowed upon it, and has Nature herself furnished it to every human being in overflowing abundance, then the thing is altogether destitute of exchange-value--whether it be an article of matter or of mind. No man can, without impertinence, transmit or convey such a commodity to his neighbour.