Transposition is the act of changing the pitches of a musical work, but not altering the relationships between theses pitches (or notes). In vocal music, transposition is often used to accommodate singers’ differing ranges. When we casually hum or sing a tune, chances are we are not humming or singing it in the key in which it was written, but rather using a different key, thereby unconsciously transposing the tune in order to use a range of pitches that feels comfortable to our particular voice. As a practical matter, one rarely transposes a single passage of music while leaving the remaining music un-transposed.
Yankee Doodle in C major. Hear Audio File
Yankee Doodle in E-flat. Hear Audio File
In the example, every feature of the Yankee Doodle melody has been retained save its pitch level: it has been transposed up a minor third from C to E-flat. In this case, transposition is equivalent to re-writing the melody in a new key. Note, however, that simple transposition never changes the “mode” of a melody from a major to a minor key (remember, the intervallic relationships between the pitches do not change).
Transposition is a term that crops up frequently in music copyright infringement disputes. This is because transposition (and specifically, melodic transposition) is commonly used by both plaintiffs and defendants in these disputes. A plaintiff typically transposes the defendant’s melody into the key of the plaintiff’s number to enhance the aural similarity between the two works. A defendant, on the other hand, will argue that to the extent his melody maps to that of the plaintiff’s, the fact that it has been transposed (i.e. written or played in a key other than that of the plaintiff’s work) suggests his melody was conceived independently of the plaintiff’s.
Among the many references to transposition in music copyright infringement opinions, those in Hein v. Harris (1923), BTE v. Bonnecaze (1999), Tisi v. Patrick (2000), and Johnson v. Gordon (2005) are particularly interesting, revealing suspicion on the part of judges towards the use of transposition by music expert witnesses.