Caleb Crain explains how difficult it is to avoid:
Suppose you want to write a brand-new popular tune. A piano has only eighty-eight keys, and the span of the human voice is even narrower. Only a few rhythms and chord progressions reliably please the palate of the masses, and myriad tunes have already been written under these constraints and are protected by copyright. Is it possible to write a new one that doesn’t echo an old one?
Is plagiarism inevitable in pop music? Thanks to combinatorics, the answer is certainly no for a song at full length. And the answer is probably still no if one focuses on just the heart of a song—whatever, legally speaking, that is. But even a genius would probably be unable to write a new pop song that doesn’t resemble some old one for at least a bar or two. When music plagiarism cases go to trial, lawyers and judges must somehow distinguish inevitable echoes from willful theft. “If a song writer is ethical,” A.J. Liebling once quipped, in a book he ghost-wrote for an unscrupulous music publisher, “he will not cop a tune within three years of its publication.” The law aspires to something a bit longer-lasting and maybe even less cynical. But to formulate a rule for distinguishing accidental from larcenous parallels is a fiendish challenge, and in attempting to rise to it, a mind could easily lose its way.
In a follow-up post, Crain features early 20th-century composer Ira B. Arnstein, who “not only ruined his musical career through the chronic litigation of music plagiarism cases; he literally went mad”:
[At the Music Copyright Infringement Resource] you can listen to the songs on both sides and make up your own mind as to whether, say, Shilkret plagiarized Arnstein, as Arnstein alleged he did (the judge’s 1933 verdict: “there was not sufficient originality in the plaintiff’s eight measures to make it worthwhile for anyone to steal them”). In a case decided in 1936, Arnstein claimed that a CBS music director had taken the gypsy-themed tune “Play, Fiddle, Play” from him; you can listen for yourself to that tune, too, as well as to Arnstein’s supposed original. In Unfair to Genius, Rosen points out that judges of the day applied conflicting rules about how to determine plagiarism in music: there was one standard in Allen v. Walt Disney Productions (1941), and a different one in Carew v. RKO Pictures (1942). The songs fought over in both cases are in the Music Copyright Infringement Resource. As are the songs at issue in Arnstein’s lawsuits against Broadcast Music, Inc. and against Cole Porter. The Cole Porter case is the show-stopper of Rosen’s book; it led to a Second Circuit ruling still used by the courts to determine whether there’s been a copyright infringement. Was a pious song of Arnstein’s degraded into, as Arnstein put it, “a song to a cow,” namely, Porter’s “Don’t Fence Me In”?