n Dec. 8, 1941, the day after the Japanese attack on Pearl Harbor, Representative Charles A. Eaton, Republican of New Jersey, made his case in the House for why the nation should enter the Second World War.

"Mr. Speaker," his speech began, "yesterday against the roar of Japanese cannon in Hawaii our American people heard a trumpet call; a call to unity; a call to courage; a call to determination once and for all to wipe off of the earth this accursed monster of tyranny and slavery which is casting its black shadow over the hearts and homes of every land."

Last year, Senator Sam Brownback, Republican of Kansas, made the case for war in Iraq this way:

"And if we don't go at Iraq, that our effort in the war on terrorism dwindles down into an intelligence operation," he said. "We go at Iraq and it says to countries that support terrorists, there remain six in the world that are as our definition state sponsors of terrorists, you say to those countries: we are serious about terrorism, we're serious about you not supporting terrorism on your own soil."

The linguist and cultural critic John McWhorter cites these excerpts in his new book, "Doing Our Own Thing: The Degradation of Language and Music and Why We Should, Like, Care" (Gotham Books). They not only are typical of speeches made in Congress on both occasions, he argues, but also provide a vivid illustration of just how much the language of public discourse has deteriorated.

Riddled with sentence fragments, run-ons and colloquialisms like "go at," Senator Brownback's speech is still intelligible, but in Mr. McWhorter's view, it is emblematic of a creeping casualness that is largely to the nation's detriment.

"We in America now are an anomaly," Mr. McWhorter said over lunch at a restaurant in Midtown Manhattan this week. "We have very little sense of English as something to be dressed up. It's just this thing that comes out of our mouths. We just talk."

Mr. McWhorter, 38, a professor of linguistics at the University of California at Berkeley and a senior fellow at the Manhattan Institute, a policy research group in New York City, is hardly the first to complain about Americans' brazen disregard for their native tongue. But unlike many others, he says the problem is not an epidemic of bad grammar.

As a linguist, he says, he knows that grammatical rules are arbitrary and that in casual conversation people have never abided by them. Rather, he argues, the fault lies with the collapse of the distinction between the written and the oral. Where formal, well-honed English was once de rigueur in public life, he argues, it has all but disappeared, supplanted by the indifferent cadences of speech and ultimately impairing our ability to think.

This bleak assessment notwithstanding, Mr. McWhorter, an intense, confident and — perhaps not surprisingly — loquacious man, is not a curmudgeon or a fuddy-duddy. Nor, for that matter, a nerd, despite a résumé that bristles with intellectual precociousness.

Self-taught in 12 languages — including Russian, Swedish, Swahili, Arabic and Hebrew, which he initially took up as a Philadelphia preschooler when he was 4 — he is a respected expert in Creole languages. (In his spare time, he is compiling the first written grammar of Saramaccan, a Creole language spoken by descendants of former slaves in Suriname.)

A college graduate at 19 and a tenured professor at 33, he has published seven previous books, including the controversial best seller, "Losing the Race: Self-Sabotage in Black America" (The Free Press, 2000), in which he accused middle-class blacks of embracing anti-intellectualism and a cult of victimology. An African-American who is an outspoken critic of affirmative action, welfare and reparations, he has aroused the ire of many liberals and earned a reputation as a conservative.

But none of these exploits, he is at pains to show, should be taken to mean that he is not hip. His conversation is peppered with knowing allusions to pop culture — Britney Spears, Tori Amos, television sitcoms, rap and Broadway. ("I'm the world's only straight musical-theater cast-album fanatic," he joked.) An experienced bass-baritone who plays cocktail piano and has performed in amateur theatrics, he illustrated a point about contemporary English usage by singing two lines from Stephen Sondheim's new musical, "Bounce." In many ways, he insists, he is a typical product of America after the 1960's, the decade to which he dates the beginning of the nation's linguistic decline.

"I cannot recite a single poem," he said. "You can take a Russian teenager and say recite some poetry, and they will give you strophes of Pushkin. We can't do it. The only equivalent for an American under a certain age is literally Dr. Seuss or theme songs."

Until the 1960's, he maintains, informal cultural expression — like the experimental prose of Beatnik writers — was relegated to outsider status. But by the end of the decade, he insists, that had changed: the counterculture went mainstream, ushering in the laid-back new linguistic regime.

Over lunch, he ticked off the evidence: the Beatles and other rock 'n' roll bands became national obsessions; "Bell Telephone Hour," a prime-time television show featuring classical music, was canceled; Hollywood began to make movies like "Easy Rider" that captured the mumbling diction of everyday speech; participants at a Dartmouth College education conference declared that creative classroom learning should be stressed over grammar rules and formal essays.

At the same time, Mr. McWhorter argued, the Free Speech Movement was spreading on college campuses — along with expletive-laden posters, sit-ins and skimpy clothes. And black English, a language traditionally spoken, not written, was becoming increasingly popular among young people.

"During a counterculture era, when we've been taught not to trust anyone over 30 and that our leaders are corrupt, naturally the speech of the oppressed becomes more attractive," he said. "It's in this era that most pop music begins to be sung in a black accent even by white people who grew up in Connecticut."

Mr. McWhorter paints an elaborate picture of a culture in linguistic upheaval, but some scholars caution against singling out the 1960's as a time of unprecedented change.

"There has always been pop culture, or low culture, alongside the high," said Robin Lakoff, a professor of linguistics at the University of California at Berkeley who studies the effects of language on shaping social attitudes. "But because low culture has traditionally been nonliterate and unattended to by the higher punditry, it tends to vanish without much of a trace. So people like John compare an imaginary golden age of only high culture products with what we have today, when low culture's products exist for posterity on tape."

She might have cited Mr. McWhorter's book as an example of low and high culture co-existing side by side. Despite its high-minded content, it is written in a breezy, colloquial style that seems paradoxically to embody some of the linguistic traits that he deplores. Sentences like "Back in the day, rhetoric was how we sang our language to the skies" and "Linguistically, America eats with its face now" are common along with conversational locutions like "however that rubs you" or "the times were a-changin'."

The book's free-wheeling prose and unorthodox usage — Mr. McWhorter frequently combines a plural subject with a singular verb — has put off at least one critic, Jonathan Yardley in The Washington Post, who ended his review with the words: "Physician, heal thyself."

Yet Mr. McWhorter, who defends his writing style in the book, says it was a deliberate choice on his part. "I wrote the book in a style that channels speech in a way I certainly could not have gotten away with 40 years ago," he admitted. In part, he said, his goal was not to sound like a scold. But his prose is also, he insisted, a reflection of the era in which he was brought up.

"I'm very much a part of this," he said.