RULERS have long kept certain powers hidden from their subjects. But this summer’s disclosures concerning the surveillance practices of the National Security Agency have made it clear that today’s freedom of expression comes at the price of a new power: the state’s ability to burrow ever deeper, by technological means, into the private language of ordinary citizens.

Not only has our government concealed this power, but it also plans to prosecute the man who had the courage to reveal it. Critics are viewed as “nihilists, anarchists, activists, Lulzsec, Anonymous, twentysomethings who haven’t talked to the opposite sex in five or six years,” in the words of Michael V. Hayden, a former N.S.A. and C.I.A. director.

In a time when speech is subjected to unprecedented scrutiny, it is worth recalling that the safest way to express a subversive thought is to clothe it in unfamiliar garb. We can learn how from another motley cast of characters, including children, rebels, beggars and scribes. Long ago, such outsiders and outlaws twisted the languages that they shared with others, making of them new and unheard things: obscure jargons, which allowed them to communicate safely among themselves.

The word jargon originally meant unintelligible noises resembling speech, like the twittering of birds. But early on, jargon became the name of the peculiar speech used by criminal groups. One of the first examples dates from 1455, when the authorities in Dijon, France, tried and condemned a band of brigands who called themselves “Coquillars,” alleging that they had plotted crimes in “a secret language that other people cannot understand.” The surviving legal records contain an inventory of the key words that the bandits used. “Vendengeur,” for example, meant “bag snatcher,” “pipeur” signified “dice player,” and “to do a King David” was to open and close a coffer.