It is important to note that the powerful rights associated with a copyright, are restricted to the work itself. A copyright does not extend to the facts and idea within a work, merely the expression of those facts and ideas. For example, a photographer that creates a picture of a tree has a copyright on their photograph, but other photographers are still free to to take and sell photographs of the same tree. Reproducing a copyrighted work would be copyright infringement, but independently creating an identical work would not be copyright infringement. The same principle holds true in music. There are a finite number of ways to create pleasing music, so there is bound to be some common series of notes that recur in songs created by different artists. As long as the musicians independently created their music, copyright infringement has not occurred. The problem then becomes, what evidence can a court use to determine when copyright infringement occurred or two songs just sound similar?