A case of cold plagiarism?

The old adage "where there's a hit, there's a writ" is certainly true of Coldplay's inescapable tune, "Viva La Vida." In December, guitar virtuoso Joe Satriani – renowned for dexterous fingers – claimed that "Viva La Vida" is a case of cold plagiarism of his 2004 melody, "If I Could Fly." (Last June, an obscure New York band called Creaky Boards also accused the British megastars of stealing "Viva La Vida" but didn't take the claim to court.)

Claims of musical theft go as far back as Wolfgang Amadeus Mozart's feuds with rival composer Antonio Salieri. But determining culpability over musical plagiarism hasn't become any easier over the centuries. Plaintiffs must first prove that the defendant had "access" to their music, and then determine that the two melodies are "similar."

But defining what constitutes a similarity can be complex. For starters, there's likely to be a difference in key, a difference in pitch, and even a slight difference in tempo to adjust for the different voice.

"No one would really have a question [about copying] if it was a book and the organization [of the material] was the same, and a few of the chapters were the same, word for word," says copyright lawyer Oren Warshavsky of New York firm Baker Hostetler. "Because it's music, it's a little harder, especially because a lot of times you're talking about the performative aspect of the music."

Still, that hasn't deterred several plaintiffs from filing lawsuits against some of popular music's biggest stars of late:

Earlier this month, an Italian court awarded an Italian songwriting duo a slice of Prince's royalties over the alleged similarities between his 1994 hit song, "The Most Beautiful Girl in the World" and their tune, "Takin' Me to Paradise." But the case faces another hearing.

A publishing company believes that rapper Lil' Wayne copied the music and melody of the 1965 Rolling Stones' tune "Play With Fire" for a song titled "Playing With Fire."

An obscure songwriting duo is taking Jay-Z and Mary J. Blige to court over the tune "Enough Cryin'." The plaintiffs purportedly sent a demo of the melody to the song's producer.

In a court of law, determining that an artist had reasonable "access" to a piece of music isn't hard to establish. In the age of Internet, TV, radio, concert tours, and stores brimming with CDs, there are ample opportunities for one artist to hear another's work.

"I would say in the Coldplay case, Satriani would have no difficulty making a case for access," says Charles Cronin, who manages the Music Copyright Infringement Project at the University of California at Los Angeles. "If he were in New Jersey in a garage and had never released a record and played only at a local diner, that would be far more difficult. Even then, it would be possible to argue some degree of access."

In the end, it all comes down to the ears of the judge and jury. But that can be very subjective from listener to listener, says Andrew Wasson, head of the Creative Guitar studio in Winnipeg, Manitoba, who became a sensation on YouTube by creating a music-theory analysis of the Coldplay and Satriani songs.

A more accurate gauge of similarity is to examine the tunes from a musicology perspective. "I'd be looking for whether the songs share basically the primary elements of music," says Mr. Wasson, who concludes that "Viva La Vida" and "If I Could Fly" are uncannily similar. "I'm looking for that melody being the same, the rhythms being the same, and the harmony or the chord changes being the same."

Even though there are a finite number of notes – 12 in a chromatic scale – it's relatively rare that you'll hear two strikingly similar works that are created independently of one another, according to Mr. Cronin. In the case of Satriani v. Coldplay, Cronin believes the two songs don't have enough commonalities to support a lawsuit. "They're really improvisatory works that are conceived in terms of sound, not in terms of notes," he says.

Whatever the outcome of the high-profile lawsuit, Coldplay singer Chris Martin may now regret a 2005 interview in which he told Rolling Stone magazine, "We're definitely good, but I don't think you can say we're that original. I regard us as being incredibly good plagiarists."