On July 4, 1960, the Eugene (Ore.) Register-Guard rang in Independence Day with a dire Associated Press report by one Norma Gauhn headlined "American Dialects Disappearing." The problem, according to "speech experts," was the homogenizing effect of "mass communications, compulsory education, [and] the mobility of restless Americans." These conformist pressures have only intensified in the half-century since...

Before you start weeping into your chowdah, though, I have some news: All these people are wrong. Not about the Boston accent, necessarily; that one might really be receding. But American linguistic diversity as a whole isn't dying - it's thriving. Despite our gut-level hunch about the direction of the language; despite the fact that 70-cent, three-minute, off-peak, coast-to-coast long-distance calls that cost four inflation-adjusted dollars in 1970 are now free; despite cheap travel, YouTube, and the globalization of film and television, American dialects are actually diverging.

There are multiple examples of such divergence. But none is as dramatic, as baffling to linguists, and as mysteriously under the collective radar as what's happening in the cities that ring the Great Lakes. From Syracuse, N.Y., in the east to Milwaukee in the west, 34 million Americans are revolutionizing the sound of English. Linguists first noted aspects of the change in the late 1960s. In 1972, three linguists, led by William Labov of the University of Pennsylvania, christened the phenomenon the Northern Cities Vowel Shift or, more simply, the Northern Cities Shift (NCS). What they observed may be the most important change in English pronunciation in centuries.

And the NCS dialect is, it appears, becoming more ordinary. Forecasting the likely growth of a dialect is tricky, but the NCS dialect appears to have spread in recent decades. Only in the United States, though: While dialect boundaries tend to blur at the edges and pay no heed to political borders, "the starkest dialect boundaries in North America are the boundaries between Detroit and Windsor and the boundaries between Buffalo" and Canada, according to Aaron Dinkin, an assistant professor of sociolinguistics at Swarthmore College. ...

When Labov first observed the NCS in the 1970s, it appeared to be a distinctly urban accent, hence its name (the Northern Cities Shift). Dinkin's research in northern and eastern New York state, however, suggests that the NCS has leaked into smaller communities there. ...

One boundary the NCS rarely crosses: race. While a linguistic segregation of black and white is typical in American dialects, "it's especially true of the NCS," according to Dinkin. "There are much bigger differences between white and black speakers in the NCS region," he says, "than in, for example, the South." ...

Aaron Dinkin is a visiting assistant professor of linguistics and coordinator of Swarthmore's phonetics laboratory.