The cardinal rule is Be Original.
Plagiarism is the act of copying someone else's written work and claiming it as your own. While the act can be illegal, as well as unethical, the term plagiarism is not used in law. Legally, it is one form of copyright infringement, so it enters into the arcane world of Intellectual Property law. When a musical composition is plagiarized, it's the copyright on the written musical score or arrangement that is being violated.
Copyright Infringement 101
Proving you hold the copyright is usually easy.
Copyright law is substantially the same in the British Commonwealth countries and the U.S. There is also an international treaty on copyrights that establishes the basics in international law.
While accusations of music usurping show up in the news quite often, less than 100 cases have actually gone through the federal courts in the United States since the 1850s, according to the UCLA Copyright Infringement Project. (http://cip.law.ucla.edu/caselist.html) As a plaintiff, you have to prove the other person copied a "substantial part" of your original work and you need to show a "substantial similarity" between the two works. Copyright come with the act of creation, so you are not required to register it, but it remains a good idea, in case you ever have to defend it in court. You can mail a copy to yourself and keep it in the sealed, postmarked package, but actually registering it with the Patent and Copyright Office is better evidence.
You have to show how your alleged copyist had access to your work to be able to copy it. If the song was a hit or you can show that she watched your video on youtube (or something like that), that is considered access enough. You also need to prove that there is a real similarity between the two pieces and that it's not just coincidence. (That is the likely source of the urban myth that taking no more than four bars isn't plagiarism.) What counts is that it is distinctive enough that people hear the connection between them and that it hasn't been changed enough to be called an original work in itself.
Conscious or unconscious
Intent matters in plagiarism cases. If you heard a piece of music somewhere and later wrote something that sounded a lot like it, that does not mean you have willfully violated their copyright. George Harrison was sued by the composer for copying the tune from "She's So Fine" for "My Sweet Lord," and claiming it as his own. The court ruled that, while there was a substantial similarity, the former Beatle had "unconsciously" infringed on the copyright.
Part or whole
For a plagiarism charge to stick, the piece being copied does not have to be any particular length, though it's hard to prove someone has expropriated a few notes. In Australia, the music publisher that has the rights to the old camp song "Kookaburra Sits in the Old Gum Tree" won a lawsuit against the '80s band, Men At Work. What they had copied was the melody of the flute interlude on the recording.
Fair Use
The Australian Copyright Council explains their version of the Fair Use exemption as allowing copying for research or study. (RMIT University: Copyright, Plagiarism and Fair Use - http://rmit.com.au/browse;ID=obcz6j8do3ll#fairuse) Proving your use is "fair" depends on all the circumstances taken together. Copying an article from a newspaper or magazine or up to 10 percent of a music piece of 10 or more pages, is allowable under Fair Use. Parody is also recognized as a form of fair use, even if the parody is designed to sound like the original. In the U.S., the parody exemption comes from the First Amendment guarantee of Freedom of Speech.
E.U. law and music pagiarism
The EU has done a lot to harmonize copyright law around the world.
All 27 members of the European Union are parties to the Berne Convention for the Protection of Literary and Artistic Works, so E.U. copyright protection is similar to the U.S.'s. Copyright protection in the U.S. falls under the Berne Convention, so it carries over to protection in the E.U. as well. European nations have also signed on to the WIPO (World Intellectual Property Organization) Treaty and follow several directives from the European parliament.
Tags: Berne Convention, Copyright Infringement, Intellectual Property, like that, original work