PHILADELPHIA -- Last winter, when a University of Pennsylvania sociologist, Elijah Anderson, first heard a colleague's summary of her forthcoming book, he thought he was hearing an echo of his own work.
Today that echo has turned into an uproar, a dispute that has set scholar against scholar and led researchers at some of the nation's most prestigious colleges to choose sides.
The charge? ''Conceptual plagiarism."
Neither Anderson nor his supporters assert that a fellow Penn sociologist, Kathryn Edin, had copied his writings in her new book, ''Promises I Can Keep: Why Poor Women Put Motherhood Before Marriage," co-written with a St. Joseph's University professor, Maria Kefalas.
Instead, they accuse the authors of appropriating concepts and ideas that sprang from Anderson's research, particularly those developed in his 1999 book, ''Code of the Street: Decency, Violence, and the Moral Life of the Inner City."
''There's serious undercitation," Anderson says.
The controversy, first reported in the Daily Pennsylvanian, raises issues that reach beyond the halls of academia. In an age of file-sharing and open-source programming, when everything from movies to music can be captured at the touch of a button and when the Internet serves as a worldwide echo chamber, who truly owns an idea?
The stakes are enormous, as countries move further from an industrial economy toward one where intellectual property is a thing of real value. And unlike the verbatim theft of written words -- a precise, quantifiable sort of plagiarism -- determining the provenance of an idea can be a mushy affair.
More than a dozen professors at schools including Princeton and Harvard universities have come to the defense of Edin and Kefalas, calling the charge of conceptual plagiarism ''absurd." In response, Anderson compiled a list of 22 similarities between the books -- both examine motherhood and marriage in the inner city -- posting the comparison on the Penn Almanac, a university website. Anderson also released a statement saying the two authors ''misled readers" by ''repeating the distinctive ideas, findings, explanations, and terms of Code without citing the source."
Edin declined to be interviewed. Kefalas, who faced questions about attribution in her previous book -- she posted a list of corrections on the St. Joseph's University website -- declined to discuss the controversy at Penn.
But in an e-mail message, Kefalas said she respected Anderson's work and had cited him more than any other ethnographer in ''Promises."
''The fact that we study some of the same issues makes some degree of conceptual overlap inevitable," she wrote, ''but in no way did we appropriate Dr. Anderson's work."
On Tuesday, a letter signed by 110 scholars who support Anderson appeared on the Almanac, the latest salvo in the dispute.
''The use of ideas is one of the most problematic areas," said John P. Lesko, a professor at Saginaw Valley State University in Michigan, where he runs the Famous Plagiarists Research Project. ''How do you prove for sure that your idea has been taken?"
Who owns an idea? That question might perhaps be answered with another: How does a clownfish smile?
In 2003, the Walt Disney Co. released an animated feature about a lovable, lost clownfish, ''Finding Nemo" -- and French children's author Franck Le Calvez said he thought he recognized his story. He had written an outline for a movie, never made, and a book, ''Pierrot Le Poisson Clown."
Le Calvez accused Disney of stealing his fish. Disney insisted ''Nemo" was its own creation.
In court, a French judge found meaningful differences between the characters.
Le Calvez lost the case. In April, he returned to court and lost again. This time, the court ruled that Le Calvez had known about ''Nemo" and had fraudulent intentions when he registered his character. He was ordered to pay about $73,000 in damages.
To people who study plagiarism, the case illustrates the complexity of trying to assign credit for overlapping ideas -- and of how serious money can ride on the outcome. ''Finding Nemo" earned Disney $340 million in box-office receipts alone.
Big money usually isn't an issue in academic and scientific publishing, which embraces a tradition of attribution and citation. But even those fields are subject to new pressures. As colleges are run more like businesses, with administrators pushing faculty members to produce not just scholarship but revenue, the credit for ground-breaking ideas has become the currency of the market.
It has also been key to securing research grants and book contracts.
Further complicating matters: Plagiarism is an ethical concept, not a legal term. The police don't arrest people for plagiarism. Nobody goes to jail. Punishment is meted out in the form of damaged reputations and lost jobs.
Copyright law offers limited protection for a writer's words and none at all for the ideas expressed by those words.
''You can't copyright an idea," said a Philadelphia licensing lawyer, Peter T. Wakiyama. ''That's Intellectual Property 101."
At Penn, the next steps are uncertain. Neither side has filed an official complaint, which would trigger a more formal inquiry by the university.
The dispute could have ended last summer, in fact, when Anderson and Edin met to discuss their books, eventually reaching a confidential agreement.
But in August, the affair became the talk of the American Sociological Association conference, held in Philadelphia. Afterward, disturbed by what he saw as official silence, Harold Bershady, Penn professor emeritus, sent an e-mail to the department faculty, making the charge of ''conceptual plagiarism." When his e-mail was leaked to the Daily Pennsylvanian, the furor ignited publicly.